Patent Publication Number: US-11392363-B2

Title: Implementing application entrypoints with containers of a bundled application

Description:
BACKGROUND 
     Field of the Invention 
     This invention relates to orchestration of roles in an application instantiated in a distributed storage and computation system. 
     Background of the Invention 
     In many contexts, it is helpful to be able to return a database or distributed application to an original state or some intermediate state. In this manner, changes to the distributed application or other database configuration parameters may be tested without fear of corrupting critical data. 
     The systems and methods disclosed herein provide an improved approach for creating snapshots of a database and returning to a previous snapshot. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through use of the accompanying drawings, in which: 
         FIG. 1  is a schematic block diagram of a network environment for implementing methods in accordance with an embodiment of the present invention; 
         FIG. 2  is a process flow diagram of a method for coordinating snapshot creation with compute nodes and storage nodes in accordance with an embodiment of the present invention; 
         FIG. 3  is a schematic diagram illustrating the storage of data within a storage node in accordance with an embodiment of the present invention; 
         FIG. 4  is a process flow diagram of a method for processing write requests in a storage node in accordance with an embodiment of the present invention; 
         FIG. 5  is a process flow diagram of a method for processing a snapshot instruction by a storage node in accordance with an embodiment of the present invention; 
         FIG. 6  is a process flow diagram of a method for performing garbage collection on segments in accordance with an embodiment of the present invention; 
         FIG. 7  is a process flow diagram of a method for reading data from a snapshot in accordance with an embodiment of the present invention; 
         FIG. 8  is a process flow diagram of a method for cloning a snapshot in accordance with an embodiment of the present invention; 
         FIG. 9  illustrates a snapshot hierarchy created in accordance with an embodiment of the present invention; 
         FIG. 10  is a process flow diagram of a method for rolling back to a prior snapshot in accordance with an embodiment of the present invention; 
         FIG. 11  illustrates the snapshot hierarchy of  FIG. 9  as modified according to the method of  FIG. 10  in accordance with an embodiment of the present invention; 
         FIG. 12  is a process flow diagram of a method for reading from a clone snapshot in accordance with an embodiment of the present invention; 
         FIG. 13  is a schematic block diagram of components for implementing orchestration of multi-role applications in accordance with an embodiment of the present invention; 
         FIG. 14  is a process flow diagram of a method for orchestrating the deployment of a multi-role application in accordance with an embodiment of the present invention; 
         FIG. 15  is a process flow diagram of a method for implementing provisioning constraints in accordance with an embodiment of the present invention; 
         FIG. 16  is a process flow diagram of a method for creating a snapshot of a multi-role application in accordance with an embodiment of the present invention; 
         FIG. 17  is a process flow diagram of a method for rolling back a multi-role application in accordance with an embodiment of the present invention; 
         FIG. 18A  is a diagram illustrating a thin clone in accordance with an embodiment of the present invention; 
         FIG. 18B  is a diagram illustrating a thick clone in accordance with an embodiment of the present invention; 
         FIG. 19  is a process flow diagram of a method for implementing a deferred thick clone in accordance with an embodiment of the present invention; 
         FIG. 20  is a diagram illustrating implantation of a fenced application clone in accordance with an embodiment of the present invention; 
         FIG. 21  is a process flow diagram of a method for implementing a fenced application clone in accordance with an embodiment of the present invention; 
         FIG. 22  is a schematic diagram of components for processing traffic in a bundled application in accordance with an embodiment of the present invention; 
         FIG. 23  is a diagram illustrating components for implementing addresses for containers of a bundled application in accordance with an embodiment of the present invention; 
         FIG. 24  is a diagram illustrating components for implementing an entrypoint to an application instance in accordance with an embodiment of the present invention; 
         FIG. 25  is a process flow diagram of a method for implementing an entrypoint to an application instance in accordance with an embodiment of the present invention; 
         FIG. 26  is a diagram illustrating implementation of a fenced clone in accordance with an embodiment of the present invention; 
         FIG. 27  is a process flow diagram of a method for implementing a fenced clone in accordance with an embodiment of the present invention; 
         FIG. 28  is a diagram illustrating implementation of a fenced clone in a cloud computing environment in accordance with an embodiment of the present invention; 
         FIG. 29  is a process flow diagram of a method for implementing a fenced clone in a cloud computing environment in accordance with an embodiment of the present invention; and 
         FIG. 30  is a schematic block diagram of an example computing device suitable for implementing methods in accordance with embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , the methods disclosed herein may be performed using the illustrated network environment  100 . The network environment  100  includes a storage manager  102  that coordinates the creation of snapshots of storage volumes and maintains records of where snapshots are stored within the network environment  100 . In particular, the storage manager  102  may be connected by way of a network  104  to one or more storage nodes  106 , each storage node having one or more storage devices  108 , e.g. hard disk drives, flash memory, or other persistent or transitory memory. The network  104  may be a local area network (LAN), wide area network (WAN), or any other type of network including wired, fireless, fiber optic, or any other type of network connections. 
     One or more compute nodes  110  are also coupled to the network  104  and host user applications that generate read and write requests with respect to storage volumes managed by the storage manager  102  and stored within the memory devices  108  of the storage nodes  108 . 
     The methods disclosed herein ascribe certain functions to the storage manager  102 , storage nodes  106 , and compute node  110 . The methods disclosed herein are particularly useful for large scale deployment including large amounts of data distributed over many storage nodes  106  and accessed by many compute nodes  110 . However, the methods disclosed herein may also be implemented using a single computer implementing the functions ascribed herein to some or all of the storage manager  102 , storage nodes  106 , and compute node  110 . 
     Referring to  FIG. 2 , the illustrated method  200  may be performed in order to invoke the creation of a new snapshot. Other than a current snapshot, which is still subject to change, a snapshot captures the state of a storage volume at a moment in time and is not altered in response to subsequent writes to the storage volume. 
     The method  200  includes receiving, by the storage manager  102  a request to create a new snapshot for a storage volume. A storage volume as referred to herein may be a virtual storage volume that may divided into individual slices. For example, storage volumes as described herein may be 1 TB and be divided into 1 GB slices. In general, a slice and its snapshot are stored on a single storage node  106 , whereas a storage volume may have the slices thereof stored by multiple storage nodes  106 . 
     The request received at step  202  may be received from a human operator or generated automatically, such as according to backup scheduler executing on the storage manager  102  or some other computing device. The subsequent steps of the method  200  may be executed in response to receiving  202  the request 
     The method  200  may include transmitting  204  a quiesce instruction to all compute nodes  110  that are associated with the storage volume. For example, all compute nodes  110  that have pending write requests to the storage volume. In some embodiments, the storage manager  102  may store a mapping of compute nodes  110  to a particular storage volume used by the compute nodes  110 . Accordingly, step  204  may include sending  204  the quiesce instruction to all of these compute nodes. Alternatively, the instruction may be transmitted  204  to all compute nodes  110  and include an identifier of the storage volume. The compute nodes  110  may then suppress any write instructions referencing that storage volume. 
     The quiesce instruction instructs the compute nodes  110  that receive it to suppress  206  transmitting write requests to the storage nodes  106  for the storage volume referenced by the quiesce instruction. The quiesce instruction may further cause the compute nodes  110  that receive it to report  208  to the storage manager  102  when no write requests are pending for that storage volume, i.e. all write requests issued to one or more storage nodes  106  and referencing slices of that storage volume have been acknowledged by the one or more storage nodes  106 . 
     In response to receiving the report of step  208  from one or more compute nodes, e.g. all compute nodes that are mapped to the storage node that is the subject of the snapshot request of step  202 , the storage manager  102  transmits  210  an instruction to the storage nodes  106  associated with the storage volume to create a new snapshot of that storage volume. Step  210  may further include transmitting  210  an instruction to the compute nodes  110  associated with the storage volume to commence issuing write commands to the storage nodes  106  associated with the storage volume. In some embodiments, the instruction of step  110  may include an identifier of the new snapshot. Accordingly, subsequent input/output operations (IOPs) transmitted  214  from the compute nodes may reference that snapshot identifier. Likewise, the storage node  106  may associate the snapshot identifier with data subsequently written to the storage volume, as described in greater detail below. 
     In response to receiving  210  the instruction to create a new snapshot, each storage node  106  finalizes  212  segments associated with the current snapshot, which may include performing garbage collection, as described in greater detail below. In addition, subsequent IOPs received by the storage node may also be processed  216  using the new snapshot as the current snapshot, as is also described in greater detail below. 
     Referring to  FIG. 3 , the method by which slices are allocated, reassigned, written to, and read from may be understood with respect to the illustrated data storage scheme. The data of the storage scheme may be stored in transitory or persistent memory of the storage node  106 , such as in the storage devices  108 . 
     For each logical volume, the storage manager  102  may store and maintain a volume map  300 . For each slice in the logical volume, the volume map may include an entry including a node identifier  302  identifying the storage node  106  to which the slice is assigned and an offset  304  within the logical volume at which the slice begins. In some embodiments, slices are assigned both to a storage node  106  and a specific storage device hosted by the storage node  106 . Accordingly, the entry may further include a disk identifier of the storage node  106  referencing the specific storage device to which the slice is assigned. 
     The remaining data structures of  FIG. 3  are stored on each storage node  106 . The storage node  106  may store a slice map  308 . The slice map  308  may include entries including a local slice identifier  310  that uniquely identifies each slice of the storage node  106 , e.g. each slice of each storage device hosted by the storage node  106 . The entry may further include a volume identifier  312  that identifies the logical volume to which the local slice identifier  310  is assigned. The entry may further include the offset  304  within the logical volume of the slice of the logical volume assigned to the storage node  106 . 
     In some embodiments, an entry in the slice map  308  is created for a slice of the logical volume only after a write request is received that references the offset  304  for that slice. This further supports the implementation of overprovisioning such that slices may be assigned to a storage node  106  in excess of its actual capacity since the slice is only tied up in the slice map  308  when it is actually used. 
     The storage node  106  may further store and maintain a segment map  314 . The segment map  314  includes entries either including or corresponding to a particular physical segment identifier (PSID)  316 . For example, the segment map  314  may be in an area of memory such that each address in that area corresponds to one PSID  316  such that the entry does not actually need to include the PSID  316 . The entries of the segment map  314  may further include a slice identifier  310  that identifies a local slice of the storage node  106  to which the PSID  316  has been assigned. The entry may further include a virtual segment identifier (VSID)  318 . As described in greater detail below, each time a segment is assigned to logical volume and a slice of a logical volume, it may be assigned a VSID  318  such that the VSIDs  318  increase in value monotonically in order of assignment. In this manner, the most recent PSID  316  assigned to a logical volume and slice of a logical volume may easily be determined by the magnitude of the VSIDs  318  mapped to the PSIDs  316 . In some embodiments, VSIDs  318  are assigned in a monotonically increasing series for all segments assigned to volume ID  312 . In other embodiments, each offset  304  and its corresponding slice ID  310  is assigned VSIDs separately, such that each slice ID  310  has its own corresponding series of monotonically increasing VSIDs  318  assigned to segments allocated to that slice ID  310 . 
     The entries of the segment map  314  may further include a data offset  320  for the PSID  316  of that entry. As described in greater detail below, when data is written to a segment it may be written at a first open position from a first end of the segment. Accordingly, the data offset  320  may indicate the location of this first open position in the segment. The data offset  320  for a segment may therefore be updated each time data is written to the segment to indicate where the new first open position is. 
     The entries of the segment map  314  may further include a metadata offset  322 . As described in detail below, for each write request written to a segment, a metadata entry may be stored in that segment at a first open position from a second end of the segment opposite the first end. Accordingly, the metadata offset  322  in an entry of the segment map  314  may indicate a location of this first open position of the segment corresponding to the entry. 
     Each PSID  316  corresponds to a physical segment  324  on a device hosted by the storage node  106 . As shown, data payloads  326  from various write requests are written to the physical segment  324  starting from a first end (left) of the physical segment. The physical segment may further store index pages  328  such that index pages are written starting from a second end (right) of the physical segment  324 . 
     Each index page  328  may include a header  330 . The header  330  may be coded data that enables identification of a start of an index page  328 . The entries of the index page  328  each correspond to one of the data payloads  326  and are written in the same order as the data payloads  326 . Each entry may include a logical block address (LBA)  332 . The LBA  332  indicates an offset within the logical volume to which the data payload corresponds. The LBA  332  may indicate an offset within a slice of the logical volume. For example, inasmuch as the PSID  316  is mapped to a slice ID  310  that is mapped to an offset  304  within a particular volume ID  312 , maps  308  and  314 , and an LBA  332  within the slice may be mapped to the corresponding offset  304  to obtain a fully resolved address within the logical volume. 
     In some embodiments, the entries of the index page  328  may further include a physical offset  334  of the data payload  326  corresponding to that entry. Alternatively or additionally, the entries of the index page  328  may include a size  336  of the data payload  326  corresponding to the entry. In this manner, the offset to the start of a data payload  326  for an entry may be obtained by adding up the sizes  336  of previously written entries in the index pages  328 . 
     The metadata offset  322  may point to the last index page  328  (furthest from right in illustrated example) and may further point to the first open entry in the last index page  328 . In this manner, for each write request, the metadata entry for that request may be written to the first open position in the last index page  328 . If all of the index pages  328  are full, a new index page  328  may be created and stored at the first open position from the second end and the metadata for the write request may be added at the first open position in that index page  328 . 
     The storage node  106  may further store and maintain a block map  338 . A block map  338  may be maintained for each logical volume and/or for each slice offset of each logical volume, e.g. for each local slice ID  310  which is mapped to a slice offset and logical volume by slice map  308 . The entries of the block map  338  map include entries corresponding to each LBA  332  within the logical volume or slice of the logical volume. The entries may include the LBA  332  itself or may be stored at a location within the block map corresponding to an LBA  332 . 
     The entry for each LBA  332  may include the PSID  316  identifying the physical segment  324  to which a write request referencing that LBA was last written. In some embodiments, the entry for each LBA  332  may further indicate the physical offset  334  within that physical segment  324  to which the data for that LBA was written. Alternatively, the physical offset  324  may be obtained from the index pages  328  of that physical segment. As data is written to an LBA  332 , the entry for that LBA  332  may be overwritten to indicate the physical segment  324  and physical offset  334  within that segment  324  to which the most recent data was written. 
     In embodiments implementing multiple snapshots for a volume and slice of a volume, the segment map  314  may additionally include a snapshot ID  340  identifying the snapshot to which the PSID  316  has been assigned. In particular, each time a segment is allocated to a volume and slice of a volume, the current snapshot identifier for that volume and slice of a volume will be included as the snapshot ID  340  for that PSID  316 . 
     In response to an instruction to create a new snapshot for a volume and slice of a volume, the storage node  106  will store the new current snapshot identifier, e.g. increment the previously stored current snapshot ID  340 , and subsequently allocated segments will include the current snapshot ID  340 . PSIDs  316  that are not filled and are allocated to the previous snapshot ID  340  may no longer be written to. Instead, they may be finalized or subject to garbage collection (see  FIGS. 5 and 6 ). 
       FIG. 4  illustrates a method  400  for executing write instructions by a storage node  106 , such as write instructions received from an application executing on a compute node  110 . 
     The method  400  includes receiving  402  a write request. The write request may include payload data, payload data size, and an LBA as well as fields such as a slice identifier, a volume identifier, and a snapshot identifier. Where a slice identifier is included, the LBA may be an offset within the slice, otherwise the LBA may be an address within the storage volume. 
     The method  400  may include evaluating  404  whether a PSID  316  is allocated to the snapshot referenced in the write request and whether the physical segment  324  corresponding to the PSID  316  (“the current segment”) has space for the payload data. In some embodiments, as write requests are performed with respect to a PSID  316 , the amount of data written as data  326  and index pages  328  may be tracked, such as by way of the data offset  320  and metadata offset  322  pointers. Accordingly, if the amount of previously-written data  326  and the number of allocated index pages  328  plus the size of the payload data and its corresponding metadata entry exceeds the capacity of the current segment it may be determined to be full at step  404 . 
     If the current segment is determined  404  to be full, the method  400  may include allocating  406  a new PSID  316  as the current PSID  316  and its corresponding physical segment  324  as the current segment for the snapshot referenced in the write request. In some embodiments, the status of PSIDs  316  of the physical storage devices  108  may be flagged in the segment map  314  as allocated or free as a result of allocation and garbage collection, which is discussed below. Accordingly, a free PSID  316  may be identified in the segment map  314  and flagged as allocated. 
     The segment map  314  may also be updated  408  to include a slice ID  310  and snapshot ID  340  mapping the current PSID  316  to the snapshot ID, volume ID  312 , and offset  304  included in the write request. Upon allocation, the current PSID  316  may also be mapped to a VSID (virtual segment identifier)  318  that will be a number higher than previously VSIDs  318  such that the VSIDs increase monotonically, subject, of course, to the size limit of the field used to store the VSID  318 . However, the size of the field may be sufficiently large that it is not limiting in most situations. 
     The method  400  may include writing  410  the payload data to the current segment. As described above, this may include writing  410  payload data  326  to the free location closest to the first end of the current segment. 
     The method  400  may further include writing  412  a metadata entry to the current segment. This may include writing the metadata entry (LBA, size) to the first free location closest to the second end of the current segment. Alternatively, this may include writing the metadata entry to the first free location in an index page  328  that has room for it or creating a new index page  328  located adjacent a previous index page  328 . Steps  410 ,  412  may include updating one or more pointers or table that indicates an amount of space available in the physical segment, such as a pointer  320  to the first free address closest to the first end and a pointer  322  to the first free address closest to the second end, which may be the first free address before the last index page  328  and/or the first free address in the last index page. In particular, these pointers may be maintained as the data offset  320  and metadata offset in the segment map  314  for the current PSID  316 . 
     The method  400  may further include updating  416  the block map  338  for the current snapshot. In particular, for each LBA  332  referenced in the write request, an entry in the block map  338  for that LBA  332  may be updated to reference the current PSID  316 . A write request may write to a range of LBAs  332 . Accordingly, the entry for each LBA  332  in that range may be updated to refer to the current PSID  316 . 
     Updating the block map  338  may include evaluating  414  whether an entry for a given LBA  332  referenced in the write request already exists in the block map  338 . If so, then that entry is overwritten  418  to refer to the current PSID  316 . If not, an entry is updated  416  in the block map  318  that maps the LBA  332  to the current PSID  316 . In this manner, the block map  338  only references LBAs  332  that are actually written to, which may be less than all of the LBAs  332  of a storage volume or slice. In other embodiments, the block map  338  is of fixed size and includes and entry for each LBA  332  regardless of whether it has been written to previously. The block map  338  may also be updated to include the physical offset  334  within the current segment to which the data  326  from the write request was written. 
     In some embodiments, the storage node  106  may execute multiple write requests in parallel for the same LBA  332 . Accordingly, it is possible that a later write can complete first and update the block map  338  whereas a previous write request to the same LBA  332  completes later. The data of the previous write request is therefore stale and the block map  338  should not be updated. 
     Suppressing of updating the block map  338  may be achieved by using the VSIDs  318  and physical offset  334 . When executing a write request for an LBA, the VSID  318  mapped to the segment  324  and the physical offset  334  to which the data is to be, or was, written may be compared to the VSID  318  and offset  334  corresponding to the entry in the block map  338  for the LBA  332 . If the VSID  318  mapped in the segment map  314  to the PSID  316  in the entry of the block map  338  corresponding to the LBA  332 , then the block map  338  will not be updated. Likewise, if the VSID  318  corresponding to the PSID  316  in the block map  338  is the same as the VSID  318  for the write request and the physical offset  334  in the block map  338  is higher than the offset  334  to which the data of the write request is to be or was written, the block map  338  will not be updated for the write request. 
     As a result of steps  414 - 418 , the block map  338  only lists the PSID  316  where the valid data for a given LBA  332  is stored. Accordingly, only the index pages  328  of the physical segment  324  mapped to the PSID  316  listed in the block map  338  need be searched to find the data for a given LBA  332 . In instances where the physical offset  334  is stored in the block map  338 , no searching is required. 
       FIG. 5  illustrates a method  500  executed by a storage node  106  in response to the new snapshot instruction of step  210  for a storage volume. The method  500  may be executed in response to an explicit instruction to create a new snapshot or in response to a write request that includes a new snapshot ID  340 . The method  500  may also be executed with respect to a current snapshot that is still being addressed by new write requests. For example, the method  500  may be executed periodically or be triggered based on usage. 
     The method  500  may include allocating  502  a new PSID  316  and its corresponding physical segment  324  as the current PSID  316  and current segment for the storage volume, e.g., by including a slice ID  310  corresponding to a volume ID  312  and offset  304  included in the new snapshot instruction or the write request referencing the new snapshot ID  340 . Allocating  502  a new segment may include updating  504  an entry in the segment map  314  that maps the current PSID  316  to the snapshot ID  340  and a slice ID  310  corresponding to a volume ID  312  and offset  304  included in the new snapshot instruction. 
     As noted above, when a PSID  316  is allocated, the VSID  318  for that PSID  316  may be a number higher than all VSIDs  318  previously assigned to that volume ID  312 , and possibly to that slice ID  310  (where slices have separate series of VSIDs  318 ). The snapshot ID  340  of the new snapshot may be included in the new snapshot instruction or the storage node  106  may simply assign a new snapshot ID that is the previous snapshot ID  340  plus one. 
     The method  500  may further include finalizing  506  and performing garbage collection with respect to PSIDs  316  mapped to one or more previous snapshots IDs  340  for the volume ID  312  in the segment map  314 , e.g., PSIDs  316  assigned to the snapshot ID  340  that was the current snapshot immediately before the new snapshot instruction was received. 
       FIG. 6  illustrates a method  600  for finalizing and performing garbage collection with respect to segment IDs  340  for a snapshot (“the subject snapshot”), which may include the current snapshot or a previous snapshot. The method  600  may include marking  602  as valid latest-written data for an LBA  332  in the PSID  316  having the highest VSID  318  in the segment map  314  and to which data was written for that LBA  332 . Marking  602  data as valid may include making an entry in a separate table that lists the location of valid data or entries for metadata in a given physical segment  324  or setting a flag in the metadata entries stored in the index pages  328  of a physical segment  324 , e.g., a flag that indicates that the data referenced by that metadata is invalid or valid. 
     Note that the block map  338  records the PSID  316  for the latest version of the data written to a given LBA  332 . Accordingly, any references to that LBA  332  in the physical segment  324  of a PSID  316  mapped to a lower-numbered VSID  318  may be marked  604  as invalid. For the physical segment  324  of the PSID  316  in the block map  338  for a given LBA  332 , the last metadata entry for that LBA  332  may be found and marked as valid, i.e. the last entry referencing the LBA  332  in the index page  328  that is the last index page  328  including a reference to the LBA  332 . Any other references to the LBA  332  in the physical segment  324  may be marked  604  as invalid. Note that the physical offset  334  for the LBA  332  may be included in the block map  334 , so all metadata entries not corresponding to that physical offset  334  may be marked as invalid. 
     The method  600  may then include processing  606  each segment ID S of the PSIDs  316  mapped to the subject snapshot according to steps  608 - 620 . In some embodiments, the processing of step  606  may exclude a current PSID  316 , i.e. the last PSID  302  assigned to the subject snapshot. As described below, garbage collection may include writing valid data from a segment to a new segment. Accordingly, step  606  may commence with the PSID  316  having the lowest-valued VSID  318  for the subject snapshot. As any segments  324  are filled according to the garbage collection process, they may also be evaluated to be finalized or subject to garbage collection as described below. 
     The method  600  may include evaluating  608  whether garbage collection is needed for the segment ID S. This may include comparing the amount of valid data in the physical segment  324  for the segment ID S to a threshold. For example, if only 40% of the data stored in the physical segment  324  for the segment ID S has been marked valid, then garbage collection may be determined to be necessary. Other thresholds may be used, such as value between 30% and 80%. In other embodiments, the amount of valid data is compared to the size of the physical segment  324 , e.g., the segment ID S is determined to need garbage collection if the amount of valid data is less than X % of the size of the physical segment  324 , where X is a value between 30 and 80, such as 40. 
     If garbage collection is determined  608  not to be needed, the method  600  may include finalizing  610  the segment ID S. Finalizing may include flagging the segment ID S in the segment map  314  as full and no longer available to be written to. This flag may be stored in another table that lists finalized PSIDs  316 . 
     If garbage collection is determined  608  to be needed, then the method  600  may include writing  612  the valid data to a new segment. For example, if the valid data may be written to a current PSID  316 , i.e. the most-recently allocated PSID  316  for the subject snapshot, until its corresponding physical segment  324  full. If there is no room in the physical segment  324  for the current PSID  316 , step  612  may include assigning a new PSID  316  as the current PSID  316  for the subject snapshot. The valid data, or remaining valid data, may then be written to the physical segment  324  corresponding to the current PSID  316  for the subject snapshot. 
     Note that writing  612  the valid data to the new segment maybe processed in the same manner as for any other write request (see  FIG. 4 ) except that the snapshot ID used will be the snapshot ID  340  of the subject snapshot, which may not be the current snapshot ID. In particular, the manner in which the new PSID  316  is allocated to the subject snapshot may be performed in the same manner described above with respect to steps  406 - 48  of  FIG. 4 . Likewise, the manner in which the valid data is written to the current segment may be performed in the same manner as for steps  410 - 412  of  FIG. 4 . In some embodiments, writing of valid data to a new segment as part of garbage collection may also include updating the block map with the new location of the data for an LBA  332 , such as according to steps  414 - 418  of  FIG. 4 . When the physical segment  324  of the current PSID  316  is found to be full, it may itself be subject to the process  600  by which it is finalized or subject to garbage collection. 
     After the valid data is written to a new segment, the method  600  may further include freeing  614  the PSID S in the segment map  314 , e.g., marking the entry in segment map  314  corresponding to PSID S as free. 
     The process of garbage collection may be simplified for PSIDs  316  that are associated with the subject snapshot in the segment map  314  but are not listed in the block map  338  with respect to any LBA  332 . The physical segments  324  of such PSIDs  316  do not store any valid data. Entries for such PSIDs  316  in the segment map  314  may therefore simply be deleted and marked as free in the segment map  314   
       FIG. 7  illustrates a method  700  that may be executed by a storage node  106  in response to a read request. The read request may be received from an application executing on a compute node  110 . The read request may include such information as a snapshot ID, volume ID (and/or slice ID), LBA, and size (e.g. number of 4 KB blocks to read). 
     The following steps of the method  700  may be initially executed using the snapshot ID  340  included in the read request as “the subject snapshot,” i.e., the snapshot that is currently being processed to search for requested data. The method  700  includes receiving  702  the read request by the storage node  106  and identifying  704  one or more PSIDs  316  in the segment map  314  assigned to the subject snapshot and searching  706  the metadata entries for these PSIDs  316  for references to the LBA  332  included in the read request. 
     The searching of step  706  may be performed in order of decreasing VSID  318 , i.e. such that the metadata entries for the last allocated PSID  316  is searched first. In this manner, if reference to the LBA  332  is found, the metadata of any previously-allocated PSIDs  316  does not need to be searched. 
     Searching  706  the metadata for a PSID  316  may include searching one or more index pages  328  of the physical segment  324  corresponding to the PSID  316 . As noted above, one or more index pages  328  are stored at the second end of the physical segment  324  and entries are added to the index pages  328  in the order they are received. Accordingly, the last-written metadata including the LBA  332  in the last index page  328  (furthest from the second end of the physical segment  324 ) in which the LBA  332  is found will correspond to the valid data for that LBA  332 . To locate the data  326  corresponding to the last-written metadata for the LBA  332  in the physical segment  324 , the sizes  336  for all previously-written metadata entries may be summed to find a start address in the physical segment  324  for the data  326 . Alternatively, if the physical offset  334  is included, then the data  326  corresponding to the metadata may be located without summing the sizes  336 . 
     If reference to the LBA  332  is found  708  in the physical segment  324  for any of the PSIDs  316  allocated to the subject snapshot, the data  326  corresponding to the last-written metadata entry including that LBA  332  in the physical segment  324  mapped to the PSID  316  having the highest VSID  318  of all PSIDs  316  in which the LBA is found will be returned  710  to the application that issued the read request. 
     If the LBA  332  is not found in the metadata entries for any of the PSIDs  316  mapped to subject snapshot, the method  700  may include evaluating  712  whether the subject snapshot is the earliest snapshot for the storage volume of the read request on the storage node  106 . If so, then the data requested is not available to be read and the method  700  may include returning  714  a “data not found” message or otherwise indicating to the requesting application that the data is not available. 
     If an earlier snapshot than the subject snapshot is present for the storage volume on the storage node  106 , e.g., there exists at least one PSID  316  mapped to a snapshot ID  340  that is lower than the snapshot ID  340  of the subject snapshot ID, then the immediately preceding snapshot ID  340  will be set  716  to be the subject snapshot and processing will continue at step  704 , i.e. the PSIDs  316  mapped to the subject snapshot will be searched for the LBA  332  in the read request as described above. 
     The method  700  is particularly suited for reading data from snapshots other than the current snapshot that is currently being written to. In the case of a read request from the current snapshot, the block map  338  may map each LBA  332  to the PSID  316  in which the valid data for that LBA  332  is written. Accordingly, for such embodiments, step  704  may include retrieving the PSID  332  for the LBA  332  in the write request from the block map  338  and only searching  706  the metadata corresponding to that PSID  316 . Where the block map  338  stores a physical offset  334 , then the data is retrieved from that physical offset within the physical segment  314  of the PSID  336  mapped to the LBA  332  of the read request. 
     In some embodiments, the block map  332  may be generated for a snapshot other than the current snapshot in order to facilitate executing read requests, such as where a large number of read requests are anticipated in order to reduce latency. This may include searching the index pages  328  of the segments  324  allocated to the subject snapshot and its preceding snapshots to identify, for each LBA  332  to which data has been written, the PSID  316  having the highest VSID  318  of the PSIDs  316  having physical segments  324  storing data written to the each LBA  332 . This PSID  316  may then be written to the block map  318  for the each LBA  332 . Likewise, the physical offset  334  of the last-written data for that LBA  332  within the physical segment  324  for that PSID  316  may be identified as described above (e.g., as described above with respect to steps  704 - 716 ). 
     Referring to  FIG. 8 , in some instances it may be beneficial to clone a storage volume. This may include capturing a current state of a principal copy of a storage volume and making changes to it without affecting the principal copy of the storage volume. For purposes of this disclosure a “principal copy” or “principal snapshot” of a storage volume refers to an actual production copy that is part of a series of snapshots that is considered by the user to be the current, official, or most up-to-date copy of the storage volume. In contrast, a clone snapshot is a snapshot created for experimentation or evaluation but changes to it are not intended by the user to become part of the production copy of the storage volume. Stated differently, only one snapshot may be a principal snapshot with respect to an immediately preceding snapshot, independent of the purpose of the snapshot. Any other snapshots that are immediate descendants of the immediately preceding snapshot are clone snapshots. 
     The illustrated method  800  may be executed by the storage manager  102  and one or more storage nodes  106  in order to implement this functionality. The method  800  may include receiving  802  a clone instruction and executing the remaining steps of the method  800  in response to the clone instruction. The clone instruction may be received by the storage manager  102  from a user or be generated according to a script or other program executing on the storage manager  102  or a remote computing device in communication with the storage manager  102 . 
     The method  800  may include recording  804  a clone branch in a snapshot tree. For example, referring to  FIG. 9 , in some embodiments, for each snapshot that is created for a storage volume, the storage manager  102  may create a node S 1 -S 5  in a snapshot hierarchy  900 . In response to a clone instruction, the storage manager  102  may create a clone snapshot and branch to a node A 1  representing the clone snapshot. In the illustrated example, a clone instruction was received with respect to the snapshot of node S 2 . This resulted in the creation of clone snapshot represented by node A 1  that branches from node S 2 . Note node S 3  and its descendants are also connected to node S 2  in the hierarchy. 
     In some embodiments, the clone instruction may specify which snapshot the clone snapshot is of. In other embodiments, the clone instruction may be inferred to be a snapshot of a current snapshot. In such embodiments, a new principal snapshot may be created and become the current snapshot. The previous snapshot will then be finalized and be subject to garbage collection as described above. The clone will then branch from the previous snapshot. In the illustrated example, if node S 2  represented the current snapshot, then a new snapshot represented by node S 3  would be created. The snapshot of node S 2  would then be finalized and subject to garbage collection and clone snapshot represented by A 1  would be created and node A 1  would be added to the hierarchy as a descendent of node S 2 . 
     In some embodiments, the clone node A 1 , and possibly its descendants A 2  to A 4  (representing subsequent snapshots of the clone snapshot), may be distinguished from the nodes S 1  to S 5  representing principal snapshots, such as by means of a flag, a classification of the connection between the node A 1  and node S 2  that is its immediate ancestor, or by storing data defining node A 1  in a separate data structure. 
     Following creation of a clone snapshot, other principal snapshots of the storage volume may be created and added to represented in the hierarchy by one or more nodes S 2  to S 5 . A clone may be created of any of these snapshots and represented by additional clone nodes. In the illustrated example, node B 1  represents a clone snapshot of the snapshot represented by node S 4 . Subsequent snapshots of the clone snapshot are represented by nodes B 1  to B 3 . 
     Referring again to  FIG. 8 , the creation of a clone snapshot on the storage node  106  may be performed in the identical manner as for any other snapshot, such as according to the methods of  FIGS. 2 through 6 . In particular, one or more segments  806  may be allocated to the clone snapshot on storage nodes  106  storing slices of the cloned storage volume and mapped to the clone snapshot. IOPs referencing the clone snapshot may be executed  808 , such as according to the method  400  of  FIG. 4 . 
     In some instances, it may be desirable to store a clone snapshot on a different storage node  106  than the principal snapshots. Accordingly, the method  800  may include allocating  806  segments to the clone snapshot on the different storage node  106 . This may be invoked by sending a new snapshot instruction referencing the clone snapshot (i.e., an identifier of the clone snapshot) to the different storage node  106  and instructing one or more compute nodes  110  to route IOPs for the clone snapshot to the different storage node  106 . 
     The storage node  102  may store in each node of the hierarchy, data identifying one or more storage nodes  106  that store data for the snapshot represented by that node of the hierarchy. For example, each node may store or have associated therewith one or more identifiers of storage nodes  106  that store a particular snapshot ID for a particular volume ID. The node may further map one or more slice IDs (e.g., slice offsets) of a storage volume to one storage nodes  106  storing data for that slice ID and the snapshots for that slice ID. 
     Referring to  FIG. 10 , one of the benefits of snapshots is the ability to capture the state of a storage volume such that it can be restored at a later time.  FIG. 10  illustrates a method  1000  for rolling back a storage volume to a previous snapshot, particularly for a storage volume having one or more clone snapshots. 
     The method  1000  includes receiving  1002 , by the storage manager  102 , an instruction to rollback a storage volume to a particular snapshot SN. The method  1000  may then include processing  1004  each snapshot that is a represented by a descendent node of the node representing snapshot SN in the snapshot hierarchy, i.e. snapshots SN+1 to SMAX, where SMAX is the last principal snapshot that is a descendent of snapshot SN (each “descendent snapshot”). For each descendent snapshot, processing  1004  may include evaluating  1006  whether the each descendent is an ancestor of a node representing a clone snapshot. If not, then the storage manager  102  may instruct all storage nodes  106  storing segments mapped to the descendent snapshot to free  1008  these segments, i.e. delete entries from the segment map referencing the descendent snapshot and marking corresponding PSIDs  316  as free in the segment map  314 . 
     If the descendent snapshot is found  1006  to be an ancestor of a clone snapshot, then step  1008  is not performed and the snapshot and any segments allocated to it are retained. 
       FIG. 11  illustrates the snapshot hierarchy following execution of the method  1000  with respect to the snapshot represented by node S 3 . As is apparent, snapshot S 5  has been removed from the hierarchy and any segments corresponding to these snapshots will have been freed on one or more storage nodes  106 . 
     However, since node S 4  is an ancestor of clone node B 1 , it is not removed and segments corresponding to it are not freed on one or more storage nodes in response to the roll back instruction. Inasmuch as each snapshot contains only data written to the storage volume after it was created, previous snapshots may be required to recreate the storage volume. Accordingly, the snapshots of nodes S 3  to S 1  are needed to create the snapshot of the storage volume corresponding to node B 1 . 
     Subsequent principal snapshots of the storage volume will be added as descendants of the node to which the storage volume was rolled back. In the illustrated example, a new principal snapshot is represented by node S 6  that is an immediate descendent of node S 3 . Node S 4  is only present due to clone node B 1  and therefore may itself be classified as a clone node in the hierarchy in response to the rollback instruction of step  1002 . 
     Note that  FIG. 11  is a simple representation of a hierarchy. There could be any number of clone snapshots, clones of clone snapshots and descendent snapshots of any of these snapshots represented by nodes of a hierarchy. Accordingly, to roll back to a particular snapshot of a clone, the method  1000  is the same, except that descendants of the clone snapshot are treated the same as principal snapshots and clones of any of these descendants are treated the same as a clone snapshot. 
     Referring to  FIG. 12 , the illustrated method  1200  may be used to execute a read request with respect to a storage volume that is represented by a hierarchy generated as described above with respect to  FIGS. 8 through 11 . The illustrated method  1200  may also be executed with respect to a storage volume that includes only principal snapshots that are distributed across multiple storage nodes, i.e., all the segments corresponding to snapshots of the same slice of the storage volume are not located on the same storage node  106 . In that case, the hierarchy stored on the storage manager  102  stores the location of the segments for each snapshot and therefore enables them to be located. 
     The method  1200  may be executed by a storage node  106  (“the current storage node”) with information retrieved from the storage manager  102  as noted below. The method  1200  may include receiving  1202  a read request, which may include such information as a snapshot ID, volume ID (and/or slice ID), LBA, and size (e.g. number of 4 KB blocks to read). 
     Note that the read request may be issued by an application executing on a compute node  110 . The compute node  110  may determine which storage node  106  to transmit the read request using information from the storage manager  102 . For example, the compute node  110  may transmit a request to obtain an identifier for the storage node  102  storing data for a particular slice and snapshot of a storage volume. The storage manager may then obtain an identifier and/or address for the storage node  106  storing that snapshot and slice of the storage volume from the hierarchical representation of the storage volume and return it to the requesting compute node  110 . For example, the storage manager  102  may retrieve this information from the node in the hierarchy representing the snapshot included in the read request. 
     In response to the read request, the current storage node performs the algorithm illustrated by subsequent steps of the method  1200 . In particular, the method  1200  may include identifying  1204  segments assigned to the snapshot ID of the read request in the segment (“the subject snapshot”). 
     The method  1200  may include searching  1206  the metadata of the segments identified in step  1204  for the LBA of the read request. If the LBA is found, the data from the highest numbered segment having the LBA in its metadata is returned, i.e. the data that corresponds to the last-written metadata entry including the LBA. 
     If the LBA is not found in any of the segments mapped to subject snapshot, then the method  1200  may include evaluating  1212  whether the subject snapshot is the earliest snapshot on the current storage node. If not, then steps processing continues at step  1204  with the previous snapshot set  1214  as the subject snapshot. 
     Steps  1204 - 1214  may be performed in the same manner as for steps  704 - 714  of the method  700 , including the various modifications and variations described above with respect to the method  700 . 
     In contrast to the method  700 , if the LBA is not found in any of the segments corresponding to the subject snapshot for any of the snapshots evaluated, then the method  1200  may include requesting  1216  a location, e.g. storage node identifier, where an earlier snapshot for the volume ID or slice ID is stored. In response to this request, the storage manager  102  determines an identifier of a storage node  106  storing the snapshot corresponding to the immediate ancestor of the earliest snapshot stored on the current storage node in the hierarchy. The storage manager  102  may determine an identifier of the storage node  106  relating to the immediate-ancestor snapshot and that stores data for a slice ID and volume ID of the read request as recorded for the ancestor nearest ancestor node in the hierarchy of the node corresponding to the earliest snapshot stored on the current storage node. 
     If the current storage node is found  1218  to be the earliest snapshot for the storage volume ID and/or slice ID of the read request, then the data the storage manager  102  may report this fact to the storage node, which will then return  1220  a message indicating that the requested LBA is not available for reading, such as in the same manner as step  714  of the method  700 . 
     If another storage node stores an earlier snapshot for the volume ID and/or slice ID of the read request, then the read request may be transmitted  1222  to this next storage node by either the current storage node or the storage manager  102 . The processing may then continue at step  1202  with the next storage node as the current storage node. The read request transmitted at step  1222  may have a snapshot ID set to the latest snapshot ID for the storage volume ID and or slice ID of the original read request. 
     The method  1200  may be performed repeatedly across multiple storage nodes  106  until the earliest snapshot is encountered or the LBA of the read request is located. 
     Referring to  FIG. 13 , storage according to the above-described methods and systems may be incorporated into an application-orchestration approach. In the illustrates approach, an orchestration layer  1300  implements a bundled application  1302  including a plurality of roles. In the following description, “bundled application” refers to a bundle of applications as implemented using the orchestration layer. A “role” is an instance of an executable that is managed by the orchestration layer as described herein as part of the bundled application. Accordingly, a “role” may itself be a standalone application, such as a database, webserver, blogging application, or any other application. Examples of roles include the roles used to implement multi-role applications such as CASSANDRA, HADOOP, SPARK, DRUID, SQL database, ORACLE database, MONGODB database, WORDPRESS, and the like. For example, in HADOOP, roles may include one or more of a named node, data node, zookeeper, and AMBARI server. 
     The orchestration layer  1300  may implement a bundled application  1302  defining roles and relationships between roles as described in greater detail below. The bundled application  1302  may include a manifest  1304  that defines the roles of the bundled application  1302 , which may include identifiers of roles and possibly a number of instances for each role identified. The manifest  1304  may define dynamic functions define how the number of instances of particular role may grow or shrink depending on usage. The orchestration layer  1300  may then create or remove instances for a role as described below as indicated by usage and one or more functions for that role. The manifest  1304  may define a topology of the bundled application  1302 , i.e. the relationship between roles, such as services of a role that are accessed by another role. 
     The bundled application  1302  may include provisioning  1306 . The provisioning  1306  defines the resources of storage nodes  106  and compute nodes  110  required to implement the bundle. The provisioning  1306  may define resources for the bundle as a whole or for individual roles. Resources may include a number of processors (e.g., processing cores), an amount of memory (e.g., RAM (random access memory), an amount of storage (e.g., GB (gigabytes) on a HDD (Hard Disk Drive) or SSD (Solid State Drive)). As described below, these resources may be provisioned in a virtualized manner such that the bundled application  1302  and individual roles  1312  are not informed of the actual location or processing and storage resources and are relieved from any responsibility for managing such resources. In particular, storage resources may be virtualized by the storage manager  102  using the methods described above such that storage volumes are allocated and used without requiring the bundled application  1302  or roles to manage the underlying storage nodes  106  and storage device  108  on which the data of the storage volumes is written. 
     Provisioning  1306  may include static specification of resources and may also include dynamic provisioning functions that will invoke allocation of resources in response to usage of the bundled application. For example, as a database fills up, additional storage volumes may be allocated. As usage of a bundled application increases, additional processing cores and memory may be allocated to reduce latency. 
     A bundled application  1302  may further include configuration parameters  1308 . Configuration parameters may include variables and settings for each role of the bundle. The configuration parameters are defined by the developer of the role and therefore may include any example of such parameters for any application known in the art. The configuration parameters may be dynamic or static. For example, some parameters may be dependent on resources such as an amount of memory, processing cores, or storage. Accordingly, these parameters may be defined as a function of these resources. The orchestration layer will then update such parameters according to the function in response to changes in provisioning of those resources that are inputs to the function. For example, CASSANDRA defines a variable Max_Heap_Size that is normally set to half the memory limit. Accordingly, as the memory provisioned for a CASSANDRA role increases, the value of Max_Heap_Size may be increased to half the increased memory. 
     The bundled application  1302  may further include action hooks  1310  for various actions that may be taken with respect to the bundled application and/or particular roles of the bundled applications. Actions may include some or all of stopping, starting, restarting, taking snapshots, cloning, and rolling back to a prior snapshot. For each action, one or more action hooks may be defined. A hook is a programmable routine that is executed by the orchestration layer when the corresponding action is invoked. A hook may specify a script of commands or configuration parameters input to one or more roles in a particular order. Hooks for an action may include a pre-action hook (executed prior to implementing an action), an action hook (executed to actually implement the action), and a post action hook (executed following implementation of the action). 
     The bundled application  1302  may define a plurality of roles  1312 . Each role may include one or more provisioning constraints. As noted above, the bundled application  1302  and roles  1312  are not aware of the underlying storage nodes  106  and compute nodes  110  inasmuch as these are virtualized by the storage manager  102  and orchestration layer  1300 . Accordingly, any constraints on allocation of hardware resources may be included in the provisioning constraints  1314 . As described in greater detail below, this may include constraints to create separate fault domains in order to implement redundancy and constraints on latency. 
     The role  1312  may define a name space  1316 . A name space  1316  may include variables, functions, services, and the like implemented by a role. In particular, interfaces and services exposed by a role may be included in the name space. The name space may be referenced through the orchestration layer  1300  by an addressing scheme, e.g. &lt;Bundle ID&gt;.&lt;Role ID&gt;.&lt;Name&gt;. In some embodiments, references to the namespace  1316  of another role may be formatted and processed according to the JINJA template engine or some other syntax. Accordingly, each role  1312  may access the variables, functions, services, etc. in the name space  1316  of another role  1312  on order to implement a complex application topology. In some instances, credentials for authorizing access to a role  1312  may be shared by accessing the namespace  1316  of that role. 
     A role  1312  may further include various configuration parameters  1318  defined by the role, i.e. as defined by the developer that created the executable for the role. As noted above, these parameters  1318  may be set by the orchestration layer  1300  according to the static or dynamic configuration parameters  1308 . Configuration parameters may also be referenced in the name space  1316  and be accessible (for reading and/or writing) by other roles  1312 . 
     Each role  1312  may include a container  1320  executing an instance  1322  of the application for that role. The container  1320  may be a virtualization container, such as a virtual machine, that defines a context within which the application instance  1322  executes, facilitating starting, stopping, restarting, and other management of the execution of the application instance  1322 . Containers  1320  may include any container technology known in the art such as DOCKER, LXC, LCS, KVM, or the like. In a particular bundled application  1302 , there may be containers  1320  of multiple different types in order to take advantage of a particular container&#39;s capabilities to execute a particular role  1312 . For example, one role  1312  of a bundled application  1302  may execute a DOCKER container  1320  and another role  1312  of the same bundled application  1302  may execute an LCS container  1320 . 
     Note that a bundled application  1302  as configured in the foregoing description may be instantiated and used or may be saved as a template that can be used and modified later. 
       FIG. 14  illustrates a method  1400  for executing a bundled application  1302  using the orchestration layer  1300 . The method  1400  may include provisioning  1402  storage and computation resources according to the provisioning  1306 . This may include allocating storage volumes according to the storage requirements, assigning the storage volumes to storage nodes  106 , and selecting a compute node  110  or storage node  106  providing the required computational resources (processor cores and memory). 
     The method  1400  may include creating  1404  role instances for the roles  1312  defined by the bundled application  1302 . As described above, this may include creating a container  1320  and instantiating the application instance  1322  of the role  1312  within the container  1320 . The order in which instances  1322  are created and started may be defined in the manifest  1304 . 
     The method  1400  may include configuring  1406  each role according to the configuration parameters  1308 , including executing any included functions to determine values for dynamic parameters. As noted above, starting a bundled application  1302  may further include setting up  1408  the roles  1312  to reference resources in the name space  1316  of another role  1312 . For example, a webserver may be configured to access a database by referencing configuration parameters and services implemented by the database. 
     The method  1400  may further include executing  1410  any hooks  1310  defined for the initial startup of the bundled applications. Accordingly, pre-startup, startup, and post startup hooks may be executed. Some or all of the functions of steps  1402 - 1410  may be defined as part of the pre-startup hook. Other functions may also be performed prior to steps  1402 - 1408  as defined by a pre-startup hook. 
     The actual commencement of execution of the instances  1322  of the bundled application  1302  may be performed in an order specified by the startup hook and may include performing any attendant functions of these instances  1322  as specified by the startup hook. Following startup, one or more other actions may be performed as specified by the developer in the post-startup hook. These actions may invoke functions of the instances  1322  themselves or executed by the orchestration layer  1300  outside of the instances  1322 , such as with respect to an operating system executing the containers  1320  for the instances  1322 . 
     The bundled application  1302  may then be accessed  1412  in order to perform the programmed functionality of the application instances  1322 . As usage occurs, processing resources will be loaded and storage may be filled. The method  1400  may further include adjusting  1414  provisioning according to this usage and may performed adjustment to configuration parameters of the roles  1312  according to this provisioning as defined by the provisioning  1306  and configuration functions  1308 . 
     As noted above, instances of roles may also be created or removed according to usage. Accordingly, where indicate by the manifest  1304 , instances  1322  for a role  1312  may be created according to steps  1402 - 1410  throughout execution of the bundled application  1302  as defined by one or more dynamic functions in the manifest  1304  for that role  1312 . 
     Referring to  FIG. 15 , the illustrated method  1500  may be used to implement provisioning constraints  1314  for a role  1312  or constraints for an entire bundled application  1302 . The method  1500  may be executed by the orchestration layer  1300 , storage manager  102 , or a combination of the two. 
     The method  1500  may include receiving  1502  the provisioning constraint  1314  for one or more roles  1312  of the bundled application  1302  and determining  1504  whether the constraint  1314  specify one or both of a fault domain constraint and a latency constraint. 
     If a latency constraint is found  1506  to be included for a role  1312 , then computational resources and storage resources to be provisioned for the role  1312  may be constrained  1508  to be co-located. In particular, latency may be specified in terms of (a) a minimum network delay, (b) a minimum network throughput, (c) an explicit constraint to place computation and storage resources in the same subnetwork, or (d) an explicit constraint to place computation and storage resources on the same node, i.e. a hybrid compute and storage node  110 ,  106  that performs the functions of both types of nodes with a single computer. 
     This constraint may be used by the orchestration layer to assign computing and storage resources to roles  1312  and storage volumes of the bundled application. For example, one or more storage volumes for the role  1312  will be assigned to storage nodes  106  that can either (a) meet the latency requirement with respect to compute nodes  110  allocated to the role  1312  (b) also provide the computational resources required for the role  1312 . 
     The orchestration layer  1300  may include a resource manager in that accounts for all of the compute storage requirements and constraints and creates a resource allocation plan. This plan describes the virtual nodes (containers  1320 ) that make up the bundled application  1302 . Each virtual node has allocations of processor cores, memory and storage volumes. The resource manager determines the compute host (compute node  110  or hybrid node) for each virtual node and a set of devices for each storage volume of the virtual node. The orchestration layer  1300  sends this mapping of the storage volumes to physical devices to the storage manager  102 , which implements the storage allocation. 
     If the constraint for a role  1312  is found  1510  to include a fault domain constraint, then storage volumes for the role  1312  may be distributed  1512  among the storage nodes  106  of the distributed storage system  100  according to this requirement. For example, if storage volume B is a redundant (e.g., replica or backup) copy of storage volume A, the fault domain constraint may indicate this fact. Accordingly, the storage manager  102  may assign storage volume B to a different storage node  106  than storage volume A. Various degrees of constraint may be specified. For example, a fault domain constraint may simply require a different storage device  108  but not require a different storage node  106 . A fault domain constraint may require that storage nodes  106  to which storage volumes are assigned by in separate subnetworks, different geographic locations, or have some other degree of separation. Similar fault domain constraints may be specified for roles  1312 , which may be constrained to execute on different compute nodes  110  in order to provide redundant services and reduce downtime. 
     The provisioning constraints  1502  based on fault domains and/or latency may be combined with one or more other constraints. For example, a performance constraint (IOPs/second) for a storage node may be imposed. Accordingly, only those compute nodes meeting the performance requirement and the fault domain and/or latency requirements will be selected for provisioning. 
     As noted above, provisioning  1306  may define a processing requirement, such as a number of processing cores and an amount of storage for a role. Accordingly, compute nodes  110  may be selected at step  1508  such that both the latency requirement and processing requirement are met. 
     Referring to  FIG. 16 , the illustrated method  1600  may be executed by the orchestration layer  1302  with respect to a bundled application  1302  in order to create a snapshot of the bundled application  1302  that can be later restored (see the method  1700  of  FIG. 17 ). 
     The method  1600  may include flushing  1602  application buffers to disk. In many instances, performance of an application is accelerated by maintaining data in a cache in memory, such that data in the cache is accessed and updated without requiring writing to a disk in many instances, as known in the art. Accordingly, this buffer may be flushed  1602  to disk by writing all valid data (i.e., not outdated due to a subsequent write) in the cache to the storage device  108  to which that data is addressed, e.g., to which the storage volume referenced by the data is assigned. 
     In a like manner, a file system flush may be performed  1604 . Performing a file system flush may include ensuring that all IOPs pending to be performed by the file system have been executed, i.e. written to disk. As for step  1602 , data written to a cache for the file system this is valid may be written to a storage device  108  to which the data is addressed, e.g., to which the storage volume referenced by the data is assigned. 
     The method  1600  may then include freezing  1606  the application instances  1322  of each role  1312 . In particular, inasmuch as each instance  1322  is executing within container  1320 , the containers  1320  for the roles  1312  may be instructed to pause execution of each instance  1322 . This may include stopping execution and saving a state of execution of each instance  1322  (state variables, register contents, program pointers, function stack, etc.). 
     The method  1600  may further include creating  1608  a snapshot of storage volumes provisioned for the bundled application. This may include executing the method  200  of  FIG. 2  or any of the above-described approaches for implementing a snapshot of a storage volume. 
     The method  1600  may further include creating  1610  a topology snapshot for the bundled application  1302 . The topology of an application may include some or all of the following information as constituted at the time of executing step  1610  a listing of the roles  1312 , which may include one or more instances  1322  of the same role  1322 , relationships between application instances  1322  of roles  1312  (name space cross-references, configuration parameters), storage volumes assigned to roles  1312 , or other information that describes the topology of the bundled application  1302 . Applications may create metadata describing their state of operation. This data may also be saved as part of the topology snapshot. 
     After the snapshot is created according to the method  1600 , the application instances may be resumed, with the application itself not suffering any down time in some embodiments. The bundled application  1302  may then continue to operate. If desired, the application may then be rolled back to the snapshot created according to the method  1600 , as described below with respect to  FIG. 17 . 
       FIG. 17  illustrates a method  1700  for rolling back a bundled application  1302  to a snapshot, such as a snapshot created according to the method  1600 . The method  1700  may be executed by one or both of the orchestration layer  1300  and the storage manager  102 . 
     The method  1700  includes receiving  1702  a rollback instruction, such as from an administrator desiring to return to a stable version of the bundled application  1302 . The remaining steps of the method  1300  may be executed in response to the rollback instruction. 
     The method  1700  may include rolling  1704  back storage volumes assigned to the bundled application  1302  to the snapshots created for the snapshot of the bundled application  1302  (e.g., at step  1608  of the method  1600 ). This may include executing the method  1000  of  FIG. 10  or performing any other approach for rolling back a storage volume to a prior state. 
     The method  1700  may include restoring  1706  application instances from the application snapshot. As described above with respect to step  1606  of the method  1600 , an application instance  1322  may be frozen. Accordingly, data describing a state of execution of the application instance  1322  may be reloaded into a container  1302  for that instance. If needed, the container for that application instance  1322  may be created and the instance  1322  loaded into it prior to loading the state of execution. This is particularly the case where the number of application instances has changed since the application snapshot was created. 
     The method  1700  may further include restoring  1708  the application topology saved for the bundled application at step  1610 . Accordingly, relationships between application instances  1322  of roles  1312  (name space cross-references, configuration parameters), storage volumes assigned to roles  1312 , or other information that describes the topology of the bundled application  1302  may be restored as it was at the time the application snapshot was created 
     The method  1700  further include executing  1710 ,  1712 ,  1714  a pre-restart hook, restart hook, and post restart hook defined for the bundled application. As described above, each hook may be a routine defined by a developer to be executed for a particular action, restarting in this case. In step  1712 , execution of the instances  1322  for the roles  1322  may be restarted, along with any other actions specified by the developer in the restart hook. 
     The bundled application  1302  as restored at steps  1704 - 1714  may then be accessed  1716  as defined by the programming of the application instances and the restored application topology. 
     Note that the snapshot of the bundled application  1302  may be restarted on different storage and compute nodes  106 ,  110  than those on which the bundled application  1302  was executing when the snapshot was created. Accordingly, the application snapshot may be restarted as a clone of the bundled application  1302  or moved to different hardware when executing the method  1700 . 
     In some instances, the hooks of steps  1710 ,  1712 ,  1714  may be different when the application snapshot is being restarted as a clone as desired by a developer. For example, a developer may desire to scale the clone application to increase or decrease a number of databases, number of partitions of a database, or other aspect of the clone application. Accordingly, the hooks of steps  1710 ,  1712 ,  1714  may implement routines to implement this increase or decrease. 
     For example, some applications are able to automatically detect the number of partitions of a database. In such instances, some or all of the hooks  1710 ,  1712 ,  1714  may reduce the number of partitions in a database of the clone applications and rely on the application to discover this change. In other instances, some or all of the hooks  1710 ,  1712 ,  1714  may be programmed to configure an application to access the database with the reduced number of partitions where the application is unable to configure itself. 
     Referring to  FIGS. 18A and 18B , a storage volume may be cloned in the form of a clone snapshot, such as according to the approach described above with respect to  FIGS. 8 through 12 . 
       FIG. 18A  illustrates the approach of  FIGS. 8 through 12 , which is referred to herein as a “thin” clone. In this approach, a segment E allocated to the clone snapshot S 2  after creation of the clone snapshot is written only to the clone snapshot. Segments A-D that were written to snapshot S 1  prior to creation of clone snapshot S 2  are not copied to snapshot S 1 . As noted above, snapshot S 2  may be on a different storage node than snapshot S 1 . As described above with respect to  FIG. 12 , reads from an application  1800  for segments A-D will therefore be routed to the storage node storing snapshot S 1 . Reads for segment E can be processed locally. 
     This results in increase latency for these reads and increases loading of the storage node  106  storing snapshot S 1 . In the case where snapshot S 1  is a production snapshot and snapshot S 2  is only for testing, this loading may be undesirable. However, copying the segments A-D to snapshot S 2  will also result in loading of the storage node  106  storing snapshot S 1 . 
       FIG. 18B  illustrates a “thick” clone wherein the segments A-D are copied to snapshot S 2 . In this manner, all reads are handled by the storage node  106  storing the snapshot S 2  and the production storage node  106  storing S 1  is not loaded. However, the process of copying the segments A-D to snapshot S 2  will also result in loading of the storage node  106  storing snapshot S 1 . 
       FIG. 19  illustrates a method  1900  for implementing a “deferred thick clone” snapshot wherein segments of snapshot S 1  are gradually copied to snapshot S 2  while avoiding impacting performance of the production storage node  106  storing snapshot S 1 . The method  1900  may be executed by the storage node  106  storing the snapshot S 2  (“the clone node”) in cooperation with the storage node  106  storing the snapshot S 1  (“the primary node”). The segments that are copied may have corresponding VSIDs as described above with respect to  FIG. 3 . The association of a VSID to a segment may maintained for the copy of the segment on the clone node. As described above, a storage volume may be divided into slices that may reside on different storage nodes  106 . Accordingly, the method  1900  may be executed separately for each slice of the storage volume. 
     The method  1900  may include creating  1902  a deferred thick clone snapshot. This may include creating a thin clone snapshot ( FIG. 8 ,  FIG. 18A ) S 2 . Creating  1902  a deferred thick clone snapshot may include allocating physical segments  324  and corresponding PSIDs  316  for each segment to be copied, such as prior to the segments being copied. In some embodiments, a user may instruct that a pre-existing thin clone snapshot is to be converted to a deferred thick clone snapshot according to the method  1900 . 
     The segment map  314  may be updated to include the slice ID  310  (mapped to offset within cloned storage volume per slice map  308 ), and VSID  318 , and possibly other information shown in  FIG. 3 , for each segment to be copied. The snapshot ID  340  in the segment map  340  may be set equal to S 2 , i.e. the snapshot identifier for the clone snapshot. The segment map  314  may be updated either prior to copying or each PSID  316  entry may be updated when the corresponding segment is copied to the physical segment  324  for that PSID  316 . 
     The method  1900  may include setting  1904  a load limit, e.g., a limit on how much copying traffic the clone node may impose on the primary node. The load limit may be specified in terms of a number of bytes per second, a number of segments that may be copied at any one time, or other limits. The load limit may be time dependent. For example, at night or other periods of low usage, the load limit may be raised since production usage of the clone node will not be significantly impaired. 
     The load limit may also specify a maximum number of read IOPs that may be requested from the primary node in a given time period, e.g., maximum IOPs/second limit. 
     The method  1900  may include evaluating  1906  whether there is a hit imbalance for any of the segments that remain to be copied from the primary node to the clone node. In particular, if a large number of read requests are being routed to the primary node for a particular segment, then copying of that segment will reduce loading of the primary node and reduce latency for the clone node. 
     Accordingly, reads routed to the primary node may be tabulated for each segment referenced. Copying of segments may then be ordered according to the number of reads, with a segment having a higher number of reads being copied before a segment with a lower number. Where N segments may be in process of being copied simultaneously, then the N segments with the N highest read counts may be selected  1908  for copying first. Where no read imbalance exists, e.g., there is no significant difference in the number of reads per segment, the segments may be copied in order, e.g. in order of increasing VSIDs. What is significant may be a predetermined value. For example, where the highest read count is less than X percent of the average read count, the imbalance may be deemed insignificant, where X is a value between 1.1 and 2 or some other predetermined value greater than one. 
     In some instances, heavily used storage volumes and segments of a storage volume may be known by a developer based on the application topology, e.g., log files with heavy write usage and low read usage may be copied last whereas heavily read data may be read first. Accordingly, the ordering of copying of segments may be specified by a developer in order to copy those segments with a high hit rate first. 
     The method  1900  may include evaluating  1910  whether the primary node  1910  has spare capacity. For example, the primary node  1910  may transmit loading information, e.g. IOPs per second, to the clone node. For example, where this loading falls below a predetermined threshold, e.g. less than Y percent of the total IOP/second capacity of the primary node, then the load limit for copying segments may be increased  1912 , where Y is predetermined value less than 100, such as 70. The amount of the load limit may be set to some predetermined function of the unused IOP/second capacity of the primary node, e.g. such that no more than Z percent of the capacity is used, such as Z=90 percent. 
     In a like manner, if the primary node is determined  1914  to be loaded, the load limit may be decreased, e.g. decreased such that the amount of unused capacity of the primary remains below an acceptable value, e.g., such that the load limit plus production loading of the primary node is less than Z percent. 
     Note that steps  1910 - 1916  may be performed at the storage device  108  level. Accordingly, loading of a storage device  108  is evaluated  1910 ,  1914  and the load limit increased  1912  or decreased  1916  based on the loading in the same manner described above. 
     Note also that the evaluations of steps  1906 ,  1910 ,  1914  may be performed at the container  1320  level. In particular, storage volumes allocated to instances  1322  that are generating higher read traffic relative to other instances  1322  may be copied before storage volumes allocated to the other instances  1322 . 
     Copying of segments according to the load limit may be performed  1918 . Steps  1906 - 1918  may be performed repeatedly until all segments are found  1920  to have been copied. 
     With reference to  FIG. 3 , Once all segments are copied the block map  338  may be rebuilt  1922  according to the copied segments. In particular, metadata (e.g., index pages  328 ) of the copied segments may be evaluated to determine the physical offset  334  of LBAs referenced in the copied segments. The entry for each LBA may then be updated to include the PSID  316  where the copied segments was written and the physical offset  334  for that LBA. As noted above, a block map  338  may be maintained for each slice of a logical storage volume. Accordingly, updating  1922  the block map may be performed for each slice referenced by the copied segments. 
     As noted above, the block map  338  indicates the location of the latest written data addressed to an LBA. Accordingly, references to an LBA  332  in a copied segment will not cause updating of the entry in the block map  338  for that LBA  332  where a later version of data has been written to that LBA  332 . 
     For example, where a copied segment referencing an LBA  332  has a lower VSID than the VSID  318  mapped to the PSID  316  in the block map for that LBA  332 , the entry for that LBA  332  in the block map  338  will not be updated for that copied segment. 
     The method  1900  may be performed in the context of cloning a bundled application  1302 . Accordingly, the rollback method of  FIG. 17  may be performed on different hardware then that on which the bundled application  1302  was executing when an application snapshot was created in order to create a clone of the bundled application. In such instances, storage volumes may be cloned as either thin clones, thick clones, or deferred thick clones. The clone application may therefore continue to access storage nodes  106  provisioned for the original bundled application  1302  until a deferred thick clone has completed copying of data from the original bundled application. 
     Referring to  FIG. 20 , a plurality of containers  1320   a - 1320   b  of a bundled application  1302  hay have addresses assigned thereto that uniquely identify them. These addresses may be different and independent from the addresses (e.g., Internet Protocol (IP) addresses) of compute nodes  110  or hybrid nodes executing the containers  1320   a - 1320   b . In the simplified illustration, there are only two containers  1320   a - 1320   b . In some applications there may be tens or even hundreds of containers  1320   a - 1320   b  each with a corresponding container address. 
     Traffic between containers  1320   a - 1320   b  may be routed according to the addresses thereof, such as according to the approach described below with respect to  FIG. 22 . The orchestration layer  1300  may configure or implement network address translation (NAT) rules  2002  that may route packets addressed to a container based on references to the address of the container in the packets. 
     The containers  1320   a - 1320   b  may have one or more storage volumes  2004  mounted thereto. As described hereinabove, storage volumes may correspond to storage devices  108  on a different computer, such as on a remote storage node  106 . Accordingly, read and write requests may be routed to the corresponding storage node  106 , such as according to NAT rules  2002 . 
     In many bundled applications, particularly HADOOP, there are many containers  1320   a - 1320   b  executing many roles and many instances of roles. Persistent data stored in the storage volumes  2004  of the containers  1320   a - 1320   b  may reference the addresses of one or more of the containers  1320   a - 1320   b . These addresses may be stored throughout persistent data for the containers  1320   a - 1320   b  and precise knowledge of the operation of the bundled application may be required to determine where they occur. 
     When the bundled application is cloned (see discussion of  FIG. 17 ), the storage volumes  2004  may also be cloned, including references to the original addresses of the containers  1320   a - 1320   b  of the original application. However, the containers  1320   a - 1320   b  of the clone may be assigned new addresses to enable distinguishing between the containers  1320   a - 1320   b  of the original application and the containers  1320   a - 1320   b  of the cloned application. These new addresses are used to route external traffic  2006  to and from the containers  1320   a ,  1320   b.    
       FIG. 21  illustrates a method that may be used to deal with this situation. The method  2100  may include cloning  2102  an application, such as in the manner described above in the discussion of  FIG. 17 . The method  2100  may presume that the original application continues operating. Where an application is simply moved, execution of the method  2100  may be omitted. 
     The method  2100  may include assigning  2104  new addresses to the containers  1320   a - 1320   b  of the clone application and creating  2106  NAT rules. The NAT rules may map the address for a container  1320   a  in the clone application to the address for the corresponding container  1320   a  in the parent application. A clone application may reproduce the topology of the parent application. Accordingly, each clone container may have a mapping in the NAT rules between the address of the each clone container and the address of the container of the parent application to which it corresponds in the topology and of which it the each clone container is a clone. 
     The NAT rules may further include an association among the addresses of the clone containers, i.e. an indication that all of the addresses of the clone containers belong to the same bundled application. 
     The method  2100  may further include receiving  2108  network traffic that is either directed or received from a container  1320   a ,  1320   b  of the clone application. The network traffic may be received by a network component programmed with the NAT rules of step  2106 , which may be a router, switch, firewall, or other network component and may be the same or different from the computer system implementing the orchestration layer  1300 . This network component may perform the remaining steps of the method  2100 . 
     If the traffic is found  2110  to be intra-bundle traffic, then the traffic is routed to a container  1320   a ,  1320   b  of the clone application using  2112  the same address as the parent application. Specifically, communication between containers of the clone application may use the same addresses as the parent application and be routed to the containers of the clone application corresponding to these addresses. 
     If the traffic is found  2110  to either originate from or be directed to a container or other computing device that is not part of the clone application. For example, if a packet is transmitted by a container  1320   a ,  1320   b  of the clone application and has a destination address that is not the address of another container  1320   a    1320   b  of the clone application (either parent or clone address), then the packet may be determined not to be intra-bundle traffic. In some instances, the clone application and parent application may be constrained to not transmit traffic to one another. In other instances, this simply does not occur since the clone and parent applications are never configured to communicate with one another. 
     In that case, traffic may be translated  2114 . In particular, packets outbound from a container  1320   a ,  1320   b  may be translated to replace references to the parent address for the container with the clone address for the container. In this manner, return traffic can be routed to the clone container rather than to the corresponding container of the parent application. 
     In a like manner, inbound traffic addressed to the clone address of a clone container may be translated to include the parent address of the clone container and transmitted to the clone container. 
       FIG. 22  illustrates an approach for virtualized network communication that may be used to implement the NAT approach described above with respect to  FIG. 21 . A host computing device, such as a storage node  106  or compute node  110  may include a host network interface controller (NIC)  2200 . The NIC  2200  may perform network communication and may have a static or dynamic IP address assigned to it. Accordingly, packets may be addressed to the host computing device using that IP address. The host NIC  2200  may be associated with an open virtual switch (OVS  2202 ). The OVS  2202  may perform NAT in order to route packets to the correct container and to ensure that outbound packets use the clone addresses rather than the parent addresses. Example approaches for performing this are described below with respect to  FIGS. 23 through 29 . 
     Referring to  FIG. 23 , in some embodiments, addressing of containers  1320  of a bundled application may be implemented on a node (compute node  110  or hybrid node) using the illustrated configuration. In particular, a kernel  2300  of the node may implement an Open Virtual Switch (OVS)  2302  that is connected to containers  1320  on the node by means of pipes  2304 . The OVS  2302  is assigned the IP address  2306  of the node and the containers  1320  are assigned addresses  2308 , which may be externally routable IP addresses. The OVS  2302  may therefore be programmed to route packets including an IP addresses  2308  to the container  1320  assigned that IP address  2308 . The OVS  2302  may be coupled to the host NIC (network interface controller)  2310  by a pipe and communicate with a network by way of the host NIC  2310 . 
     In this manner, containers  1320  may be assigned externally routable IP addresses and therefore may be portable. In particular, a container may be moved to a different node and still be addressable by the same address by way of the OVS  2302  on the new node. 
     Referring to  FIG. 24 , an application instance  1322  may implement an entrypoint  2400 . As known in the art, an entrypoint may be a point in an executable file that is executed first when that file is executed. Accordingly, the entrypoint  2400  is programmed by a developer of the application and is exposed for use by an executing host system. In a like manner, each container  1320  is programmed to host execution of an application instance  1322  and is programmed to invoke the entrypoint of the application instance  3122  it is hosting. 
     In some embodiments, an orchestration agent  2402  executes on a node executing one or more containers  1320  and corresponding application instances  1322  of a bundled application  1302  (“the subject node”). The orchestration agent  2402  may implement an agent entrypoint  2404  and modify the container  1320  to refer to the agent entrypoint  2404 . For example, prior to starting execution of the container  1320 , an executable image of the container  1320  may be modified to refer to the agent entrypoint  2404  rather than to the entrypoint  2400  of the application instance  1322 . Alternatively, modification to refer to the agent entrypoint  2404  may be performed after starting execution of the container  1320  but prior to invoking of the entrypoint  2400  of the application instance  1322 . 
     The orchestration layer  1300  may provide the agent entrypoint  2404  with one or more operation variables  2406  that instruct the agent entrypoint  2404  as to what operation is being performed. Actions may include initial creation, starting, stopping, restarting, cloning, moving, rolling back or other actions performed with respect to a container  1320 . The agent entrypoint  2404  may define executable code that processes one or more operation variables  2406  and performs actions corresponding to the one or more operation variables. In some embodiments, the orchestration agent  2402  may host or access operation scripts  2408 . For example, for a given operation variable  2406 , the agent entrypoint may execute an operation script  2408  corresponding to that operation variable. The scripts  2408  may be stored locally on the subject node or accessed from a remote repository. 
     The scripts  2408  and/or agent entrypoint  2404  may include executable code that invokes the entrypoint  2400  of the application instance  1322 . In this manner, the orchestration layer  1300  may execute one or more actions prior to starting an application instance  1322  in order to implement customized actions, such as hooks  1310  specified by a developer as part of creation, starting, restarting, snapshotting, moving, cloning, rolling back, or any of the other actions described herein as being performed with respect to a bundled application  1302 . 
       FIG. 25  illustrates a method  2500  for using an agent entrypoint  2404  to facilitate use of a container in combination with an OVS  2302  (see  FIG. 23 ). 
     The method  2500  may include creating  2502  a container  1320  on the subject node and loading  2504  an application instance  1322  into the container. This may include loading a single image that includes an image of the container  1320  pre-loaded with the image of the application instance  1322 . Steps  2502  and  2504  may be invoked by the orchestration layer as part of deployment, cloning, moving or other actions performed with respect to a container  1320  of a bundled application  1302 . Were the container  1320  is a DOCKER container, step  2502  may include creating  2502  the container with the parameter “net=none” such that the container  1320  does not attempt to connect to a DOCKER bridge. Instead, the container  1320  may be connected to an OVS  2302  as described below. 
     The method  2500  may further include configuring  2506  the agent entrypoint  2404 . In particular, executable code or instructions from the orchestration layer  1300  may be transmitted from the orchestration layer  1300  to the orchestration agent  2402  on the subject node, where this executable code or instructions includes the executable for the agent entrypoint  2404  and one or more operation variables  2406  or just the one or more operation variables  2406 . In the latter case, the orchestration agent  2402  may configure a pre-loaded agent entrypoint  2404  to include the one or more operation variables  2406 . 
     The method  2500  may further include setting  2508  the agent entry point  2404  as the entrypoint for the application instance  1322  in the container  1320 . As noted above, this may be performed before or after starting execution of the container  1320  and may be performed by the orchestration agent  2402 . 
     The container  1320  may then execute  2510  the agent entrypoint  2404 . In particular, when it starts execution, the container  1320  finds an entrypoint of a loaded application and executes it. Accordingly, this function will result in execution of the agent entrypoint  2404  due to the modification of step  2508 . 
     In some embodiments, the agent entrypoint  2404  may then execute  2512  an operation script  2408 , such as the operation script  2408  referred to by the one or more operation variables  2406  set at step  2506 . 
     In the illustrated example, the operation script includes instructions to enable the establishment of a connection to an OVS  2302  (see  FIG. 23 ). For example, the operation script  2408  may instruct the agent entrypoint  2404  to wait until the OVS is found  2514  up and executing. The operation script  2408  may then invoke connecting  2516  of the container  1320  to the OVS  2302  and the host NIC  2310  through the OVS  2302 . Once a connection to the OVS  2302  and to the host NIC  2310  is established through the OVS  2302 , the method  2500  may include invoking, by the agent entrypoint  2404 , execution  2518  of the entrypoint  2400  of the application instance  1322 , either with or without executing any other preparatory actions specified in the operation script  2408 . 
     In some embodiments, a script may also be executed by the application instance  1322  that is specific to the operation specified by the one or more operation variables  2406 . For example, the agent entrypoint  2404  or orchestration layer  1300  may pass an argument to the application instance  1322 , such as upon invoking the application entrypoint  2400 . This argument may be an operation variable  2406  or a reference to a script or other file. The application instance  1322  may then execute  2520  this script or file in order to implement a particular operation. For example, the script or file may be a post-action hook  1310  provided by a developer for the application instance to be performed following a particular action (create, start, clone, move, rollback, etc.). 
     Note that steps  2514 - 2516  are particular to the case where an OVS  2302  is used to connect to a container and may be omitted in cases where other connection approaches are used. Accordingly, the illustrated approach for implementing entrypoints may be used in a general case that is not specific to use with an OVS  2302 . 
       FIG. 26  illustrates an approach for implementing a fenced clone (see  FIGS. 20-22 ) using an OVS  2302 . In the illustrated approach, containers  1320  of a clone application are assigned the IP addresses  2600  of the corresponding container  1320  of the parent application. 
     The OVS  2302  implements flows  2602  using a mapping between the parent addresses  2600  and the clone addresses  2604 . In particular, a particular container  1320  in the parent bundled application  1320  and the corresponding clone of that container  1320  may be assigned the same IP address  1320 . The clone container is also assigned a clone IP address that is unique to the clone container. A mapping in the flow  2602  therefore maps the parent IP address to the clone IP address. This mapping may be received by the OVS  2302  from the orchestration layer  1300 , which may, for example, assign the clone IP addresses as part of the cloning process and maintain a mapping between the clone IP addresses and the parent IP addresses. 
       FIG. 27  illustrates a method  2700  for implementing a fenced clone using the approach illustrated in  FIG. 26 . The method  2700  may be executed by the OVS  2302  on the subject node. 
     The method  2700  may include detecting receipt  2702  of ARP (address resolution protocol) requests. The OVS  2302  may be configured, such as by the orchestration layer  1300 , as a proxy for the clone IP addresses  2604  and include a mapping of MAC (machine access code) addresses to IP addresses for containers connected to the OVS  2302 . Accordingly, if an ARP request is received by the OVS  2302  and found  2704  to include an IP address for which the OVS  2302  is a proxy, the OVS  2302  will return  2706  the MAC address for the container  1320  assigned that IP address. 
     For example, if the ARP request includes the clone IP address  2604  of a container  1320 , the OVS  2302  may return a MAC (machine access code) address for that container  1320 . The OVS  2302  may be configured to send a proxy ARP only for an IP address that is not actually plumbed to an interface, e.g., the host NIC  2310 . Since the parent IP address  2600  is plumbed to an interface in some embodiments, there is no need to have a proxy ARP for that. The clone IP address  2604  is not plumbed to any interface and therefore the OVS  2302  sends the proxy ARP for the clone IP address  2604  in some embodiments. However, if both parent container  1320  and corresponding clone container  1320  are on the same node, the OVS  2302  may readily be configured to return the MAC address for the clone container  1320  in response to an ARP for the clone IP address and return the MAC address for the parent container  1320  in response to an ARP for the parent IP address. 
     The method  2700  may include detecting  2708  incoming packets, i.e. packets received from a network. If the packets include a clone IP address  2604  for a clone container  1320 , these addresses are replaced  2710  with the corresponding parent IP address as specified in the flows  2602  and the packet is forwarded  2712  over the pipe  2304  to the container  1320  assigned the corresponding parent IP address. 
     In particular, if either of the source or destination IP addresses in the packet include a clone IP address  2604  for the cloned application, these IP addresses will be replaced with their corresponding parent IP addresses. Accordingly, if a clone container A on a remote node communicates with clone container B on the subject node, the packet following step  2710  will include the IP address of the parent container for container A as the source address and the IP address of the parent container for container B as the destination address. In this manner, traffic external to the node is routed using the unique clone addresses and avoids conflict with traffic for the parent application. However, upon reaching the clone containers  1320 , the traffic includes the parent IP addresses and therefore is consistent with any persistent references to the parent IP addresses. 
     In a like manner, if an outgoing packet is detected  2714  by the OVS  2302  to include a parent IP address  2600  as either the source or destination, each parent IP address  2600  is replaced  2716  with its corresponding clone address  2604  and forwarded  2718  to the destination address following step  2716 , which may be a clone address  2604  or the original destination address if it was not one of the parent IP addresses  2600  mapped in the flow  2602 . 
     If a packet is neither incoming nor outgoing, i.e. it is local traffic between containers  1320  on the subject node, the packet is routed  2720  by the OVS  2302  accordingly. In particular, the packet is sent to the clone container  1320  referenced by the parent IP address set as the destination of the packet. 
       FIG. 28  illustrates an approach for implementing addressing of containers  1320  in a cloud computing environment, such as using virtual computing nodes in a cloud computing system. Virtual computing nodes may be embodied as EC2 (Elastic Compute Cloud) nodes  2800  implemented by AWS (AMAZON Web Services). 
     As known in the art an EC2  2800  may be assigned a primary IP address  2802  and a secondary IP addresses  2804 . As also known in the art, EC2 nodes  2800  may be associated with a virtual private circuit VPC  2806  such that communication among EC2 nodes  2800  of the VPC  2806  may be performed using either address  2802 ,  2804 . However, VPC access controls  2808  only permit communication outside of the VPC  2806  using the primary addresses  2802  for the EC2 nodes  2800 . 
     In some implementations, an EC2  2800  may implement an OVS  2810  that is assigned the primary address  2802  of the EC2. Accordingly, communication using the primary address  2802  may be performed through the OVS  2810 . 
     In the illustrated embodiment, the container  1320  may implement a VNIC (virtual network interface controller)  2812  that is connected to a second OVS  2814 , such as by means of a pipe. The OVS  2814  may implement one or more NAT rules  2816  that map a port  2618  of the primary address  2802  to a port  2820  of the secondary address  2804 . As shown, the OVS  2814  may be coupled to the OVS  2810 . In some embodiments, the OVS  2814  is implemented as a DOCKER bridge. 
     Traffic sent from the secondary address  2804  may therefore be mapped by the OVS  2814  to a particular port  2818  of the primary address  2802  in the NAT rules  2816  and routed externally from the VPC  2806  using the primary address  2802  as the source address. Return traffic addressed to a port  2818  the primary address  2802  may then be translated back to the corresponding port port  2820  of the secondary IP address  2804  using the NAT rules  2816 . The translated traffic may then be routed by the OVS  2814  to that port  2820  of the secondary IP address mapped to the port  2818  in the return traffic. 
       FIG. 29  illustrates a method  2900  for performing network communication using the approach shown in  FIG. 28 . 
     The method  2900  may include provisioning  2902  an EC2  2800  in AWS. For example, the orchestration layer  1300  may request provisioning of the EC2  2800  from AWS for use by a bundled application  1300 . 
     The method  2900  may further include the orchestration layer  1300  loading  2904  a container  1320  into the EC2 and instantiating an additional OVS  2814  for the container  1320 . In some instances, an EC2 will implement an OVS  2810  by default. In others, both OVS  2810  and  2814  are instantiated by a user of the EC2, which is the orchestration layer  1300  in some embodiments. In some embodiments, step  2906  further includes instantiating a VNIC for the container  1320  (see, e.g., description of  FIG. 22 ). 
     In some embodiments, the application instance  1322  and container  1320  hosting it may be configured by the orchestration layer  1300  to use one or both of the OVSs  2810 ,  2814  using the approach for implementing entrypoints described above with respect to  FIGS. 24 and 25 . 
     The method  2900  may further include requesting  2908 , by the orchestration layer  1300 , assignment of a secondary IP address  2804  to the container  1320  loaded at step  2904  and plumbing  2910  the secondary address to the container  1320 . The secondary IP address  2804  may be selected based on its use. For example, some applications require two IP addresses to function. Accordingly, an available secondary IP address  2804  may be selected and assigned at step  2908 . 
     In another use case, the secondary IP address  2804  may be selected by the orchestration layer  1300 , to be the parent IP address of the parent container  1320  of the container loaded at step  2904 . In this use case, the primary address  2802  of the EC2 provisioned at step  2902  may be selected to be the clone IP address 
     In another use case, the secondary IP address  2804  may be used as a portable IP address that can be moved along with the container  1320  if needed. Accordingly, the secondary IP address  2804  may be assigned by the orchestration layer  1300  and reassigned if the container  1320  is moved to a different location (see discussion of  FIG. 23 ). 
     The method  2900  may further include programming  2912  the OVS  2814  with one or more NAT rules with respect to the secondary IP address  2804 . The NAT rules may make use of port numbers to route traffic to the secondary IP address  2804 . For example, traffic from the secondary IP address  2804  may be assigned an otherwise unused port number for the primary IP address  2802 . Traffic from the container  1320  having a source set to the secondary IP address  2804  may be modified to replace the secondary IP address  2804  with the primary IP address  2802  and replace the port number  2820  to a port number  2818  of the primary IP address  2802 . Inbound traffic including that port number  2818  from another EC2, another container  1320 , or another computing device may then be modified to change the destination address from the primary IP address  2802  to the secondary IP address  2804  and possibly to include the port  2820  of the secondary IP address  2804  corresponding to that port number  2818  in the NAT rules  2816 . 
     In particular, ports of the secondary IP address  2804  may be implemented. For example, port A1 of the secondary IP address  2804  may be mapped to port P1 of the primary IP address  2802  and port A2 of the secondary IP address  2804  may be mapped to port P2 of the primary IP address  2802 . Any number of ports of the secondary IP address may be assigned to unique ports to enable addressing of specific ports of the container  1320 , such as ports assigned to particular network services. 
     The container  1320  and the application instance  1322  hosted by it may then commence operation and transmit and receive traffic from various other entities. If traffic is found  2914  by the OVS  2814  to be sent to or received from another EC2  2800  in the same VPC, then the traffic is routed  2916  according to the secondary IP addresses  2804 , i.e. the OVS  2814  will route the traffic to the EC2  2800  and container  1320  to which the secondary IP address  2804  in the destination field of the traffic is assigned. 
     If traffic is found  2914  to be sent to or received from an entity outside of the VPC including the OVS  2814 , the OVS  2814  may perform  2918  NAT. As described above, references to a secondary address  2804  in outbound traffic may be replaced with the primary address  2802  and a port assigned to that secondary address  2804  (and possibly the specific port of the secondary address  2804  referenced in the outbound traffic). The modified traffic may then be transmitted to the destination specified in the outbound traffic 
     For inbound traffic, references to a first port number assigned to a secondary address  2804  may cause the OVS  2814  to replace the primary IP address  2802  with the secondary address  2804  mapped to that port. Likewise, the first port number may be replaced with a second port number of the secondary address  2804  mapped to the first port number. The modified traffic may then be forwarded by the OVS  2814  to the container  1320  assigned the secondary IP address  2804 . 
       FIG. 30  is a block diagram illustrating an example computing device  3000 . Computing device  3000  may be used to perform various procedures, such as those discussed herein. The storage manager  102 , storage nodes  106 , compute nodes  110 , and hybrid nodes, may have some or all of the attributes of the computing device  3000 . 
     Computing device  3000  includes one or more processor(s)  3002 , one or more memory device(s)  3004 , one or more interface(s)  3006 , one or more mass storage device(s)  3008 , one or more Input/output (I/O) device(s)  3010 , and a display device  3030  all of which are coupled to a bus  3012 . Processor(s)  3002  include one or more processors or controllers that execute instructions stored in memory device(s)  3004  and/or mass storage device(s)  3008 . Processor(s)  3002  may also include various types of computer-readable media, such as cache memory. 
     Memory device(s)  3004  include various computer-readable media, such as volatile memory (e.g., random access memory (RAM)  3014 ) and/or nonvolatile memory (e.g., read-only memory (ROM)  3016 ). Memory device(s)  3004  may also include rewritable ROM, such as Flash memory. 
     Mass storage device(s)  3008  include various computer readable media, such as magnetic tapes, magnetic disks, optical disks, solid-state memory (e.g., Flash memory), and so forth. As shown in  FIG. 30 , a particular mass storage device is a hard disk drive  3024 . Various drives may also be included in mass storage device(s)  3008  to enable reading from and/or writing to the various computer readable media. Mass storage device(s)  3008  include removable media  3026  and/or non-removable media. 
     I/O device(s)  3010  include various devices that allow data and/or other information to be input to or retrieved from computing device  3000 . Example I/O device(s)  3010  include cursor control devices, keyboards, keypads, microphones, monitors or other display devices, speakers, printers, network interface cards, modems, lenses, CCDs or other image capture devices, and the like. 
     Display device  3030  includes any type of device capable of displaying information to one or more users of computing device  3000 . Examples of display device  3030  include a monitor, display terminal, video projection device, and the like. 
     Interface(s)  3006  include various interfaces that allow computing device  3000  to interact with other systems, devices, or computing environments. Example interface(s)  3006  include any number of different network interfaces  3020 , such as interfaces to local area networks (LANs), wide area networks (WANs), wireless networks, and the Internet. Other interface(s) include user interface  3018  and peripheral device interface  3022 . The interface(s)  3006  may also include one or more peripheral interfaces such as interfaces for printers, pointing devices (mice, track pad, etc.), keyboards, and the like. 
     Bus  3012  allows processor(s)  3002 , memory device(s)  3004 , interface(s)  3006 , mass storage device(s)  3008 , I/O device(s)  3010 , and display device  3030  to communicate with one another, as well as other devices or components coupled to bus  3012 . Bus  3012  represents one or more of several types of bus structures, such as a system bus, PCI bus, IEEE 1394 bus, USB bus, and so forth. 
     For purposes of illustration, programs and other executable program components are shown herein as discrete blocks, although it is understood that such programs and components may reside at various times in different storage components of computing device  3000 , and are executed by processor(s)  3002 . Alternatively, the systems and procedures described herein can be implemented in hardware, or a combination of hardware, software, and/or firmware. For example, one or more application specific integrated circuits (ASICs) can be programmed to carry out one or more of the systems and procedures described herein. 
     In the above disclosure, reference has been made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific implementations in which the disclosure may be practiced. It is understood that other implementations may be utilized and structural changes may be made without departing from the scope of the present disclosure. References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     Implementations of the systems, devices, and methods disclosed herein may comprise or utilize a special purpose or general-purpose computer including computer hardware, such as, for example, one or more processors and system memory, as discussed herein. Implementations within the scope of the present disclosure may also include physical and other computer-readable media for carrying or storing computer-executable instructions and/or data structures. Such computer-readable media can be any available media that can be accessed by a general purpose or special purpose computer system. Computer-readable media that store computer-executable instructions are computer storage media (devices). Computer-readable media that carry computer-executable instructions are transmission media. Thus, by way of example, and not limitation, implementations of the disclosure can comprise at least two distinctly different kinds of computer-readable media: computer storage media (devices) and transmission media. 
     Computer storage media (devices) includes RAM, ROM, EEPROM, CD-ROM, solid state drives (“SSDs”) (e.g., based on RAM), Flash memory, phase-change memory (“PCM”), other types of memory, other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store desired program code means in the form of computer-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer. 
     An implementation of the devices, systems, and methods disclosed herein may communicate over a computer network. A “network” is defined as one or more data links that enable the transport of electronic data between computer systems and/or modules and/or other electronic devices. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a computer, the computer properly views the connection as a transmission medium. Transmissions media can include a network and/or data links, which can be used to carry desired program code means in the form of computer-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer. Combinations of the above should also be included within the scope of computer-readable media. 
     Computer-executable instructions comprise, for example, instructions and data which, when executed at a processor, cause a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. The computer executable instructions may be, for example, binaries, intermediate format instructions such as assembly language, or even source code. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the described features or acts described above. Rather, the described features and acts are disclosed as example forms of implementing the claims. 
     Those skilled in the art will appreciate that the disclosure may be practiced in network computing environments with many types of computer system configurations, including, an in-dash vehicle computer, personal computers, desktop computers, laptop computers, message processors, hand-held devices, multi-processor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, mobile telephones, PDAs, tablets, pagers, routers, switches, various storage devices, and the like. The disclosure may also be practiced in distributed system environments where local and remote computer systems, which are linked (either by hardwired data links, wireless data links, or by a combination of hardwired and wireless data links) through a network, both perform tasks. In a distributed system environment, program modules may be located in both local and remote memory storage devices. 
     Further, where appropriate, functions described herein can be performed in one or more of: hardware, software, firmware, digital components, or analog components. For example, one or more application specific integrated circuits (ASICs) can be programmed to carry out one or more of the systems and procedures described herein. Certain terms are used throughout the description and claims to refer to particular system components. As one skilled in the art will appreciate, components may be referred to by different names. This document does not intend to distinguish between components that differ in name, but not function. 
     It should be noted that the sensor embodiments discussed above may comprise computer hardware, software, firmware, or any combination thereof to perform at least a portion of their functions. For example, a sensor may include computer code configured to be executed in one or more processors, and may include hardware logic/electrical circuitry controlled by the computer code. These example devices are provided herein purposes of illustration, and are not intended to be limiting. Embodiments of the present disclosure may be implemented in further types of devices, as would be known to persons skilled in the relevant art(s). 
     At least some embodiments of the disclosure have been directed to computer program products comprising such logic (e.g., in the form of software) stored on any computer useable medium. Such software, when executed in one or more data processing devices, causes a device to operate as described herein. 
     While various embodiments of the present disclosure have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the disclosure. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. The foregoing description has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. Further, it should be noted that any or all of the aforementioned alternate implementations may be used in any combination desired to form additional hybrid implementations of the disclosure.