Abstract:
A system, method, computer program, and/or computer readable medium for providing hierarchical interception for applications within isolated environments The computer readable medium includes computer-executable instructions for execution by a processing system. The computer-executable instructions may be for installing interceptors, configuring interceptors, preloading shared libraries, using trampoline functions, removal of interceptors, mapping between resources inside and outside the isolated environment, providing an interception database, loading the interception database, redirection of resources, and providing the hierarchy of interceptors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/862,979 filed on Apr. 15, 2013 titled SYSTEM AND METHOD FOR HIERARCHICAL INTERCEPTION WITH ISOLATED ENVIRONMENTS, now issued U.S. Pat. No. 8,943,501 issued on Jan. 27, 2015, which is a continuation of U.S. application Ser. No. 12/813,618 filed on Jun. 11, 2010 titled SYSTEM AND METHOD FOR HIERARCHICAL INTERCEPTION WITH ISOLATED ENVIRONMENTS, now issued U.S. Pat. No. 8,464,256 issued on Jun. 11, 2010, which is a continuation-in-part and claims priority from U.S. application Ser. No. 12/421,691 filed on Apr. 10, 2009 titled SYSTEM AND METHOD FOR APPLICATION ISOLATION now issued U.S. Pat. No. 8,341,631 issued on Dec. 25, 2012. This application also claims priority from U.S. patent application Ser. No. 12/421,692 filed on Apr. 10, 2009 titled SYSTEM AND METHOD FOR APPLICATION ISOLATION, now issued U.S. Pat. No. 8,904,004 issued on Dec. 2, 2014 and claims priority from U.S. patent application Ser. No. 12/421,694 filed on Apr. 10, 2009 titled SYSTEM AND METHOD FOR APPLICATION ISOLATION, now issued U.S. Pat. No. 8,782,670 issued on Jul. 15, 2014, each of which are incorporated herein by reference in their entirety. This application is related to U.S. patent application Ser. No. 12/334,654 filed on Dec. 15, 2008 titled METHOD AND SYSTEM FOR PROVIDING STORAGE CHECKPOINTING TO A GROUP OF INDEPENDENT COMPUTER APPLICATIONS, now issued U.S. Pat. No. 8,880,473 issued on Nov. 4, 2014, to U.S. patent application Ser. No. 12/334,655 filed on Dec. 15, 2008 titled METHOD AND SYSTEM FOR PROVIDING STORAGE CHECKPOINTING TO A GROUP OF INDEPENDENT COMPUTER APPLICATIONS now issued U.S. Pat. No. 8,195,722 issued on Jun. 5, 2012, each of which are incorporated herein by reference in their entirety. This application is related to U.S. patent application Ser. No. 12/334,660 filed on Dec. 15, 2008 titled METHOD AND SYSTEM FOR PROVIDING CHECKPOINTING TO WINDOWS APPLICATION GROUPS, to U.S. patent application Ser. No. 12/334,663 filed on Dec. 15, 2008 titled METHOD AND SYSTEM FOR PROVIDING CHECKPOINTING TO WINDOWS APPLICATION GROUPS, now issued U.S. Pat. No. 8,752,058 issued on Jun. 10, 2014, to U.S. patent application Ser. No. 12/334,666 filed on Dec. 15, 2008 titled METHOD AND COMPUTER READABLE MEDIUM FOR PROVIDING CHECKPOINTING TO WINDOWS APPLICATION GROUPS, now issued U.S. Pat. No. 8,281,317 issued on Oct. 2, 2012, and to U.S. patent application Ser. No. 12/334,671 filed on Dec. 15, 2008 titled METHOD AND COMPUTER READABLE MEDIUM FOR PROVIDING CHECKPOINTING TO WINDOWS APPLICATION GROUPS, now issued U.S. Pat. No. 8,752,049 issued on Jun. 10, 2014 each of which are incorporated herein by reference in their entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not Applicable 
     NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION 
     A portion of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C.F.R. §1.14. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains generally to enterprise computer systems, computer networks, embedded computer systems, wireless devices such as cell phones, computer systems, and more particularly to methods, systems and procedures (i.e., programming) for providing application isolation for multiple applications running on a host operating system and live migration of applications within and between isolated environments. 
     2. Description of Related Art 
     In many environments one of the most important features is to ensure that one running application doesn&#39;t affect other running applications, and that the crash of one application doesn&#39;t compromise other running applications. In many environments applications share system resources, libraries and hardware, which exposes subtle interconnects between seemingly unrelated applications. 
     Several approaches have been developed addressing this fundamental problem. The first level of application isolation is provided by the operating system. Modern operating systems such as Linux, UNIX, Windows2000, NT, XP and Vista provide some level of application isolation through the use of processes, and the underlying hardware memory management unit. The use of processes generally ensure than one running application process cannot address memory owned and used by other processes. This first level of isolation does not address the use of shared resources, such as files, file systems, shared memory, and libraries, so other approaches have been developed 
     In U.S. Pat. No. 6,496,847 Bugnion et al. teach the use of a virtual machine monitor (VMM) with a protected host operating system (HOS). This invention partially solves the isolation problem by placing every application into its own VMM. The solution requires the use of a VMM subsystem and in some cases a customized operating system. U.S. Pat. No. 6,496,847 does not provide isolation at the level of individual applications, but for entire operating systems with all the applications within it. It does not address the problem of application isolation with multiple natively running applications on one host computer. 
     In U.S. Pat. No. 6,601,081 Provino et al. teach the use of a virtual machine for a plurality of application programs. As with U.S. Pat. No. 6,496,847 the use of a VM subsystem simply moves the problem to a different layer, and does not address the fundamental issue of application isolation with several natively running applications on one host computer. 
     In U.S. Pat. No. 7,028,305 Schaefer teaches a system for creating an application protection layer to separate an application from the host operating system. Shaefer primarily teaches how to intercept the Windows registry to capture configuration information for Windows application and how to create a virtual operating environment for the application. Access to files is provided via a virtual file system, access to registry information via the virtual registry etc. For Unix and MacOS few specific teachings are presented. 
     A related challenge to deployment of applications is that a running application generally cannot be moved without first shutting down the application and re-starting it on a new server. The terminate-restart cycle disconnects all users, terminates all sessions, and generally leaves the application services unavailable for some period of time. With the move to “Software as a Service (SaaS)”, “Cloud Computing” or “Hosted Services” software services must be available at all times; anything else is considered unacceptable by customers. Today, service agreements for hosted services generally have penalties associated with any amount of downtime and application being unavailable. 
     In U.S. Pat. No. 7,213,246 Rietshote et al teach “Failing over a virtual machine” (VM) to a second system. Applications within the VM are failed over along with the entire VM. The failover requires a VM subsystem and does not address the issue of failing over the application without the presence of a virtual machine infrastructure. 
     In U.S. Ser. No. 11/567,983 Travostino et al teach “seamless live migration of virtual machines across optical networks”. The live migration requires a virtual machine and does not address live migration of the individual applications within the virtual machine or between virtual machines. 
     In U.S. patent application Ser. Nos. 12/334,654, 12/334,655 and Ser. No. 12/334,657 Havemose et. al (“Havemose”) teach checkpointing of application groups on Linux and the use of checkpointing for failover and live migration. In U.S. patent application Ser. Nos. 12/334,660, 12/334,663, 12/334,666 and Ser. No. 12/334,671Backensto et. al. (“Backensto”) teach checkpointing of application groups on Windows operating systems and the use of checkpointing for failover and live migration. Both of Havemose and Backensto, included by reference above, teach application checkpointing and live migration that work transparently over the underlying operating system without the need of a virtual machine subsystem. 
     The present invention provides a system and methods to create an application isolation environment where applications can run unmodified, on un-modified operating systems without requiring any virtual environments, virtual machines or virtual machine monitors. The present invention also teaches how to manage and handle applications that share libraries and resources, and how to handle complex multi-process applications. In one embodiment an implementation in the Linux environment is disclosed, in another embodiment an implementation on Windows is disclosed. 
     Another aspect of the present invention is a system and methods to perform live migration of applications within and between isolated environments without requiring virtual machines, virtual machine monitors or other additional infrastructure. 
     BRIEF SUMMARY OF THE INVENTION 
     A method, system, apparatus and/or computer program are disclosed for achieving application isolation and application live migration for single and multi-process applications and their associated resources. The application isolation and application live migration is provided without requiring any changes to the host operating system kernel or requiring any changes to the applications. The application isolation and application live migration is fully transparent to both operating system and application and automatically adjusts for resources such as memory, storage, and CPUs being allocated and released. The application isolation is provided in an interception layer interposed between the individual applications and the operating system and an interception database. Additionally, the application live migration is provided in s shared library pre-loaded into each application during loading and initialization of the application. Preferably, any functional changes to system calls are done exclusively within the interception layer and interception database, and only in the context of the calling application. 
     Another aspect of the present invention relates to a computer readable medium comprising instructions for application and application group isolation and for application live migration The instructions are for installing the applications into the isolated environment, running the application in the isolated environment, un-installing applications from the isolated environment, configuring the isolated environments, live migrating applications within and between isolated environments, deploying the isolated environments and configuring the isolated environments and live migration 
     DEFINITIONS 
     The terms “Windows” and “Microsoft Windows” is utilized herein interchangeably to designate any and all versions of the Microsoft Windows operating systems. By example, and not limitation, this includes Windows XP, Windows Server 2003, Windows NT, Windows Vista, Windows Server 2008, Windows Mobile, and Windows Embedded. 
     The terms “Linux” and “UNIX” is utilized herein to designate any and all variants of Linux and UNIX. By example, and not limitation, this includes RedHat Linux, Suse Linux, Ubuntu Linux, HPUX (HP UNIX), and Solaris (Sun UNIX). 
     The term “node” and “host” are utilized herein interchangeably to designate one or more processors running a single instance of an operating system. A virtual machine, such as VMWare or XEN VM instance, is also considered a “node”. Using VM technology, it is possible to have multiple nodes on one physical server. 
     The terms “application” is utilized to designate a grouping of one or more processes, where each process can consist of one or more threads. Operating systems generally launch an application by creating the application&#39;s initial process and letting that initial process run/execute. In the following teachings we often identify the application at launch time with that initial process. 
     The term “application group” is utilized to designate a grouping of one or more applications. 
     The terms “checkpointer”, “checkpointing” and “checkpointing service” are utilized herein interchangeably to designate a set of services which 1) capture the entire state of an application and store all or some of the application state locally or remotely, and 2) restore the entire state of the application from said stored application state. The checkpointer may include the following components: dynamic link library (“checkpoint library”), loadable kernel module (“checkpointer kernel module”), a control process to monitor and coordinate an application group, and a merge utility to merge full and incremental checkpoints. The checkpointing services run on all nodes where the application groups run or are configured to run 
     The terms “checkpoint”, “taking a checkpoint”, and “checkpoint file” are utilized herein interchangeably to describe the data captured by the checkpointing service. Generally, the checkpoint files are written to local disk, remote disk or memory. The terms “checkpoint restore” and “restore from checkpoint” are used interchangeably to describe the process of restoring an application from a checkpoint. The term “checkpoint-terminate” is used to describe the process of taking a checkpoint immediately followed termination of the application by the checkpointer before the application is allowed to run again. 
     The terms “live migration”, “application live migration”, and “migration” are utilized herein to describe the process of moving a running application from one isolated environment to another, including the isolated environment as necessary. Any clients connected to the running application are preferably unaware that the application is being moved, and are preferably unaffected by the application migration. 
     The term “fork( )” is used to designate the operating system mechanism used to create a new running process. On Linux, Solaris, and other UNIX variants, a family of fork( ) calls is provided. On Windows, one of the equivalent calls is “CreateProcess( )”. Throughout the rest of this document we use the term “fork” to designate the functionality across all operating systems, not just on Linux/Unix. In general fork( ) makes a copy of the process making the fork( ) call. This means that the newly created process has a copy of the entire address space, including all variables, I/O etc of the parent process. 
     The term “exec( )” is used to designate the operating system mechanism used to overlay a new image on top of an already existing process. On Linux, Solaris, and other UNIX a family of exec( ) calls is provided. On Windows, the equivalent functionality is provided by e.g. “CreateProcess( )” via parameters. Throughout the rest of this document we use the term “exec” to designate the functionality across all operating systems, not just Linux/Unix. In general, exec( ) overwrites the entire address space of the process calling exec( ). A new process is not created and data, heap and stacks of the calling process are replaced by those of the new process. A few elements are preserved, including but not limited to process-ID, UID, open file descriptors and user-limits. 
     The term “Barrier” and “Barrier Synchronization” is used herein to designate a type of synchronization method. A Barrier for a group of processes and threads is a point in the execution where all threads and processes must stop at before being allowed to proceed. Barriers are typically implemented using semaphores, mutexes, Locks, Event Objects, or other equivalent system functionality. Barriers are well known in the art and will not be described further here. 
     In the following we use commonly known terms including but not limited to “process”, “process ID (PID)”, “thread”, “thread ID (TID)”, “thread local storage (TLS)”, “instruction pointer”, “stack”, “kernel”, “kernel module”, “loadable kernel module”, “heap”, “stack”, “files”, “disk”, “CPU”, “CPU registers”, “storage”, “memory”, “memory segments”, “address space”, “semaphore”, “loader”, “system loader”, “system path”, “sockets”, “TCP/IP”, “Inter-process communication (IPC), “Asynchronous Procedure Calls (APC)” and “signal”. These terms are well known in the art and thus will not be described in detail herein. 
     The term “transport” is utilized to designate the connection, mechanism and/or protocols used for communicating across the distributed application. Examples of transport include TCP/IP, Message Passing Interface (MPI), Myrinet, Fibre Channel, ATM, shared memory, DMA, RDMA, system buses, and custom backplanes. In the following, the term “transport driver” is utilized to designate the implementation of the transport. By way of example, the transport driver for TCP/IP would be the local TCP/IP stack running on the host. 
     The term “interception” is used to designate the mechanism by which an application re-directs a system call or library call to a new implementation. On Linux and other UNIX variants interception is generally achieved by a combination of LD_PRELOAD, wrapper functions, identically named functions resolved earlier in the load process, and changes to the kernel sys call table. On Windows, interception can be achieved by modifying a process&#39; Import Address Table and creating Trampoline functions, as documented by “Detours: Binary Interception of Win32 Functions” by Galen Hunt and Doug Brubacher, Microsoft Research July 1999”. Throughout the rest of this document we use the term interception to designate the functionality across all operating systems. 
     The term “file context” or “context” is used in relation with file operations to designate all relevant file information. By way of example, and not limitation, this includes file name, directory, read/write/append/execute attributes, buffers and other relevant data as required by the operating system. 
     The term “transparent” is used herein to designate that no modification to the application is required. In other words, the present invention works directly on the application binary without needing any application customization, source code modifications, recompilation, re-linking, special installation, custom agents, or other extensions. 
     The terms “private and isolated environment” and “isolated environment” are used herein interchangeably to designate the private area set aside for application isolation, as described in further detail below. 
     The present invention provides application isolation at several levels: 1) during installation, all installation and registration information is intercepted and installation is re-directed to a private and isolated environment, 2) during launch of an application the installation information is retrieved and provided to the application again via interception, and 3) during access to external resources interception of all access is re-directed as necessary. The combination of all levels of isolation provides for fully transparent application isolation. Thus at all times, access to resources, configuration and run-time information is intercepted and redirected. 
     By way of example, and not limitation, for embodiments within Windows operating systems, access to the Windows Registry is intercepted and included in the application isolation. 
     Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only: 
         FIG. 1  is a block diagram of the core system architecture showing two applications, the interception layer, and the interception database. 
         FIG. 2  is a block diagram illustrating installation and running of applications 
         FIG. 3  is a block diagram illustrating un-installation 
         FIG. 4  is a block diagram illustrating the Interception Database 
         FIG. 5  is a block diagram illustrating running application groups 
         FIG. 6  is a block diagram illustrating running multiple application groups concurrently 
         FIG. 7 . is a block diagram illustrating installation-free deployment 
         FIG. 8 . is a block diagram illustrating administration 
         FIG. 9  is a block diagram illustrating various deployment scenarios 
         FIG. 10  is a block diagram illustrating interception data and control flow 
         FIG. 11  is a block diagram illustrating checkpointing within an isolated environment 
         FIG. 12  is a block diagram illustrating interception data and control flow with checkpointing activated 
         FIG. 13  is a block diagram illustrating Interception Layer implementation 
         FIG. 14  is a block diagram illustrating checkpointing and restoring of application groups within an isolated environment 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring more specifically to the drawings, for illustrative purposes the present invention will be disclosed in relation to  FIG. 1  through  FIG. 14 . It will be appreciated that the system and apparatus of the invention may vary as to configuration and as to details of the constituent components, and that the method may vary as to the specific steps and sequence, without departing from the basic concepts as disclosed herein. 
     0. Introduction 
     The context in which this invention is disclosed is one or more applications being installed, running and accessing local and remote resources. Without affecting the general case of multiple applications, the following scenarios often depict and describe one or two applications as applicable. Multiple applications are handled in a similar manner. 
     1. Application Isolation—Overview 
       FIG. 1  illustrates by way of example embodiment  10  the overall structure of the present invention. The following brief overview illustrates the high-level relationship between the various components; further details on the inner workings and interdependencies are provided in the following sections.  FIG. 1 . Illustrates by way of example embodiment  10  two applications A  22  and B  26  loaded in memory  14  on a node  12 . The interception layers  16 ,  18 , and checkpointing libraries CKPT lib.  17 ,  19  are interposed between the applications  22 ,  26  and the system libraries  20  and operating system  21 . The interception database  28  provides system-wide persistent interception information and configuration information for the isolated environments. The interception layers  16 , 18  combined with the Interception database  28  provides application isolation  24 . The checkpointer libraries  17 , 19  together with the interception layers  16 , 18  provide live migration. System resources, such as CPUs  36 , I/O devices  34 , Network interfaces  32  and storage  30  are accessed using the operating system. Devices accessing remote resources use some form of transport network  38 . By way of example, system networking  32  may use TCP/IP over Ethernet transport, Storage  32  may use Fibre Channel or Ethernet transport, and I/O may use USB. The present invention access and arbitrate resources through the operating system and does not work at the transport level. 
     2. Application Isolation—Installing and Running Applications 
       FIG. 2  illustrates by way of example embodiment  40  installation of a typical application “AppXYZ”  42 . The Interception Layer (IL)  50  intercepts all calls to system libraries and the operating system. IL  50  communicates with the Interception Database (IDB)  58  to create a private and isolated environment where the application can execute without depending on or affecting other parts of the environment. By way of example, and not limitation, first the installation process requests a resource  44 , such as opening a file. The resource request is intercepted by IL  50  and a request to create  54  a private instance of the resource is made to the Interception Database (IDB)  58 . The IDB  58  is a system wide database containing mappings  60 ,  62 ,  64  between the resources as the application  42  requests them  60 , and their private values inside the isolated environment  62 , subject to global exceptions  64 . Further details on the IDB are given in section  4  below. By way of example, and not limitation, if the resource request  44  was to create a file in C:\Program Files\AppDir, the IDB may map that to a private location  62 , such as D:\private\AppXYZ\C\Program Files\AppDir. So while AppXYZ  42  operates under the assumption that it&#39;s working on C:\Program Files\AppDir, in reality all access has been intercepted and re-directed to a private and isolated environment in D:\private\AppXYZ\C\Program Files\AppDir. The IDB  58  returns  54  the private resource to IL  50 , which returns the resource handle  46  to the application  42 . As the application  42  uses the resource  46  it operates under the assumption that the original resource request was satisfied, and is unaware that all resources have been relocated to a private and isolated environment. When use of the resource is terminated  48 , the IL  50  sends a message to the IDB  58  that the resource currently is inactive  56 . All mappings are maintained in the IDB  58  after the installation finishes as they may be needed after the initial request. 
       FIG. 2  also illustrates, by way of example embodiment  40 , how an application  42  runs after being installed. As resources are opened, used, and freed, the same steps as disclosed above are used. As the application  42  executes, it generally access or create resources not used during installation. By way of example, if AppXYZ  42  is a word processor, the user may create a document and save it to storage. That document did not exist as part of the installation process, but is handled using the same mechanisms previously taught. As the user choose to create a new document, AppXYZ  42  makes a request  44  to have the file created. This is intercepted by the IL  50  and forwarded  52  to the IDB  58 . The IDB creates a mapping between the Applications  42   s  public document name  60 , and the private and isolated document name  62 . As with Application  42  information stored in the IDB  58 , so is the application data information stored persistently until un-installation. 
     In a preferred embodiment the interception layer is implemented in a shared library and preloaded as part of the load process. 
     At times it may be desirable to store some user-data outside the isolated environment, such as on a central file server. In a preferred embodiment, this is supported by specifying which resource locations should remain fixed and public in the global exceptions  64 . Such public resources are not translated into the isolated environment. 
     3. Application Isolation—Uninstalling Applications 
       FIG. 3  illustrates by way of example embodiment  80 , un-installation of a typical application AppXYZ  82 . The un-installation uses and requests resources  84 , which are intercepted by the IL  86  and redirected  88  by the IDB  90 , as disclosed above. All actions, such as deletion of files, are re-directed to the private and isolated location. When the un-install terminates, sometimes called exit( ), the exit is intercepted  92  by the IL  86 , and forwarded  94  to the IDB  90 . The IDB  90  removes all entries mapping  100  application AppXYZ  82  resources  96  against its isolated environment  98 . The application is now uninstalled, and all isolation information has been removed. 
     4. Application Isolation—Interception Database and Resource Mapping 
     The Interception Database (IDB) is a system wide database containing mappings between the resources as the application requests them, and their private values inside the isolated environment.  FIG. 4  illustrates, by way of example embodiment  120 , the Interception Database (IDB)  122 , and its various components. The IBD  122  contains two main components, a rules engine  130  and the core resource mappings  132 . The rules engine  130  contains the main high-level configuration information  124  as provided by an administrator  126 . The rules engine  130  and its configuration information  124  includes, but is not limited to, information designating the base directory for installing the isolated environment, specific exceptions  138  to the resource mappings and the general mechanism used to create the mappings. The administrator  126  defines exceptions  138  as needed. The global exceptions contain all resources that should not be remapped to the isolated environments. Examples include, but are not limited to, shared storage, shared devices, network resources, and system-wide resources. 
     The resource mapping  132  maintains mapping between public resources  134  and the corresponding private and isolated resources  136 . The resource mapping  132  also consults the global exceptions  138  prior to translating any public to private or private to public resource requests. 
     Resources take many forms including but not limited to files, fonts, shared libraries, shared devices, and storage. On Microsoft Windows the Registry is an important component and contains system wide configuration information used by most applications. Some resources, such as data files, tend to be local to the individual applications, while e.g. fonts tend to be shared between multiple applications. 
     Access to files is handled by the IL ( FIGS. 2-50 ) intercepting all file operations between the application and the system libraries and operating systems. Examples include, but are not limited to open( ), fopen( ), write( ), read( ), close( ), seek( ), remove( ) and the Windows equivalents. Generally these functions either contain a public file name as part of the arguments, or a file handle to an already established file. The files names are remapped as disclosed above, to an isolated environment, and any further reference to the handle is automatically re-directed to the isolated environment. File operations that return information, are translate back to the public values. By way of example, and not limitation, if the applications ask for “current directory”, the public name, as the application expects is returned, and not the private name within the isolated environment. By way of further example, if the current directory is located on shared storage included the global exceptions  138 , the directory is returned un-translated, as it&#39;s subject to the exception handling. 
     File, paths and other resource names can be specified both as absolute values or relative values. By way of example, and not limitation, an absolute path for a document file may be “C:\MyDocuments\myfile.doc”, while a relative reference may be “ . . . \docs\myfile.doc”. Absolute references are resolved as previously disclosed by consulting the public resources  134 , private resources  136  and global exceptions  138 . Relative addresses are resolved in a multi-step process: First relative names are converted to absolute names and then the absolute name is converted as previously disclosed. This mechanism ensures fully transparent support of both absolute and relative naming of all resources. 
     Fonts pose particular problems, as fonts reside both in application-specific directories and global system directories, such as “C:\Windows\Fonts” on Windows and “/usr/X11R6/lib/X11/fonts/” and “/usr/share/fonts/” on Linux. An application may install font both into one or more global font directories as well as application-specific directories. All shared-fonts directories are included in the Global Exceptions  138  as they should be accessed directly. If during installation additional fonts are installed, they are installed according to the policy chosen by the administrator  126 . Prior to installation, the administrator chooses if application-installed fonts are allowed to be placed in the global fonts directory or if they should be placed in the isolated environment. The rules engine  130  consults this administrative choice and upon receiving a request to enumerate the font directory will include isolated-environment fonts if so configured. If the application installs its fonts into its own file structure, the fonts are treated as normal files and are not subject to the automatic enumeration as the application knows where to look for its application-specific fonts. 
     Modern operating systems share components across multiple applications. Such shared libraries also pose a special case. On Windows Dynamic Link Libraries (DLLs) and on Linux/UNIX shared objects (.so files) are examples of such shared components. On Window shared libraries primarily reside in C:\Windows and C:\Windows\System32, but can sit anywhere. On Linux/Unix the primary locations are ‘/usr/lib’, ‘/usr/X11/lib’ and the entire /usr/lib/ directory structure. The loader of the operating system traverses the system PATH to find any requested shared library, but this can be manually or programmatically changed as part of the load process. The PATH is set using environment variables both on Windows and Linux. In order to intercept loading of shares libraries the present invention loads the application in stead of using the system loader directly. This enables interception of library loading done by the loader. If during installation additional shared libraries are installed, they are installed according to the policy chosen by the administrator  126 . Prior to installation, the administrator chooses if application-installed libraries are allowed to be placed in a global directory or if they should be placed in the private and isolated environment. If the libraries are placed into the private and isolated environment, the load PATH is adjusted to search the private location. 
     As with files, libraries can be loaded with both absolute and relative addresses. The load process handles the resource mapping as disclosed above. In all cases, the loading must follow the same path and address resolution as the system loader provides. 
     If the application installs its shared libraries into its own file structure, the libraries are treated as normal files and are not subject to an adjusted PATH or load-order as the application knows where to look for its application-specific libraries. In the preferred embodiment, if the application installs new shared libraries, they are installed into the isolated environment 
     One of the most significant sources of application incompatibilities, and one of the motivators for the present invention, is shared library conflict. By way of example, and not limitation, if a shared library is loaded on the system, and a new application installs an older version of the library, the older version may overwrite the newer version and render other applications non-functional based on having their shared library replaced by an incompatible older version. This is a common problem on both the Windows and Linux platforms. Using the preferred embodiment disclosed above, the application would install the older library into its isolated environment and therefore not affect other applications. The application would load and use the older library without ever being aware that it was provided from the isolated environment, and other applications running on the system would be unaffected by the installation of the older library. 
     Microsoft Windows uses a special configuration system generally referred to as “the Registry”. The registry contains configuration, installation and un-installation information for applications on the system. When an application installs on a Windows system, it uses the registry to store values such as “home directory”, “recent files”, etc. The preferred embodiment on Windows systems additionally include interception of all registry information, and ensures that installation and runtime information that would normally go into the registry, in stead is stored and maintained in the IDB. During installation of a Windows application all registry information is thus stored in the IDB and not the registry. When an application requests registry information, the information is provided from the IDB, and not the registry. This ensures complete application isolation from the registry. 
     The isolated environment contains all application files and shared resources and their respective mappings. These are all preserved persistently on local or remote storage and can be archived, copied and restored as any other set of files. Specifically, the isolated environment directory structure can be copied to a different node, and used directly to start the application on that node. 
     So far the Interception database has been described as a “database”. Based on the teachings above, it&#39;s readily apparent to anyone skilled in the art, that the only requirement is that updates to the resource tables  134 ,  136  and  138  be atomic at the record level. This functionality can be readily implemented in a variety of ways, including using Java&#39;s ConcurrentHashMap( ), the Windows .NET equivalents, or by custom programming the data structures and locking. Furthermore, preferably concurrent access to the Interception Database translations is provided. In an alternate implementation such a custom interception database is used in stead of a full database. 
     5. Application Isolation—Interception Data and Control Flow 
       FIG. 10  illustrates by way of example embodiment  240  the data and control flow in more detail. By way of example, and not limitation, consider first an environment with the present invention inactive. An application  242  calls a write( )  243  operation. The write operation is resolved by the operating system loader and directed  244  to the system libraries  248  and operating system  250 , and ultimately writes data to storage  251 . Return value is returned  246  to the caller  243  within the calling application  242 . 
     By way of example, and not limitation, consider an environment with the present invention active. An application  252  calls a write( )  253  operation. As disclosed in above, the write( ) is intercepted  254  by the interception layer  262 . Parameters to the write( ) call are translated by the Interception Database  264  and the rules for the isolated environment  266  and the file context and parameters of the calling write are adjusted to point to the isolated environment. The write call is then forwarded  268  to the system libraries  258  and operating system  260  as were the case with the present invention inactive. The return value  266  from the write is returned to the IL  262  which, using the IDB  264 , maps the result back into the original context and returns the value  256  to the caller  253 . The application  252  issuing the write  253  operating is thus unaware that the write is being intercepted and re-directed to the isolated environment. All translation and isolation is performed outside the application  252 , and before the write operation ever reaches the system libraries  258  or operating system  260 . 
     A specific example, using ANSI C, further illustrates the IL  262  and IDB  264  translations. Consider an example where a file is opened for writing, a small text is written, and the file is closed using the following code 
     int main(void) 
     { 
     
         
         
           
             char const *pStr=“small text”; 
             FILE *fp=fopen(“/home/user/newfile.txt”, “w”) 
             if (fp !=null)
           fwrite(pStr,strlen(pStr),1,fp);   
         
             fclose(fp)
 
}
 
           
         
       
    
     The call to fopen( ) returns a file pointer, which the fwrite( ) operation uses to write data to the file. The call to fopen( ) includes the file name “/home/user/newfile.txt” as the first parameter. The Interception Layer  262  intercepts the call to fopen( ) and changes the actual filename to the corresponding location in the isolated environment before passing  268  the call on to the system library implementation  258 . The following fwrite( ) operation is unaware that the file pointer points to the isolated environment and simply writes the data. Finally, fclose( ) is called to close the file. The file pointer still points to the isolated environment and the close proceeds as a close would without the present invention active. 
     6. Implementation Considerations for the Interception Layer 
     In a preferred implementation the interception layer is implemented as a shared library and pre-loaded into each application process&#39; address space as part of loading the application. Shared libraries are implemented in such as way that each instance of the interception layer share the same code, but have their own private data, where said private data corresponds to the interception and resource translations undertaken on behalf of the particular application process and its threads. In a multi-process application the interception layer is therefore comprised of one interception layer per application process, and together the process-level interception layers comprise the interception layer. On most diagrams within these disclosures we therefore show one interception layer corresponding to the fact that only one shared library has been loaded, and where necessary point out that each process is being intercepted separately. The application process interception layers are generally referred to as “application process interception layer” on the diagrams. 
     A related issue with interception is that intercepted functions may call other intercepted functions. As long as said calls are performed using public intercepted names, the previous teachings fully describe the interception. At times shared library developers take shortcuts and don&#39;t use the public names, but refer directly to the implementation using a private name. In such cases, the interceptor must overlay a copy of the intercepted shared library code using fully resolved public function names. 
       FIG. 13  illustrates by way of example embodiment  360 , an application  361  with three application processes: process A  362  with its preloaded application process interception layer  363 , process B  364  with its preloaded application process interception layer  365 , and process C  366  with its preloaded application process interception layer  367 . The Interception Layer  368  for all the application processes is comprised of the three individual application process interception layers  363 ,  365 , and  367 . 
     In an alternate implementation, a separate application interception layer process is created, and the individual application process interception layers communicate with the application interception layer using sockets, TCP/IP, pipes or other inter-process communication (IPC). This is generally less attractive, as it requires the creation of a separate process and additional communication overhead. 
     7. Application Isolation with Application Groups 
     At times multiple applications share data, libraries and work in combination. By way of example, and not limitation, a Microsoft Word document may include or require a Microsoft Excel spreadsheet. In general any number of applications may need to collaborate and share data. So far the approach has been to isolate applications so that, to continue the example, if Word and Excel were installed separately, they would both be isolated and not able to work together. To enable sharing between pre-designated applications, the applications need to be grouped together in an application group and installed inside the same isolated environment.  FIG. 5  illustrates by way of example embodiment  140 , an application group  141  with three individual applications operating within the present invention. Any other number of applications is handled in a similar manner. The administrator  152  pre-defines the application group  141  and the individual applications within the group: App- 1   142 , App- 2   144  and App- 3   146 . During launch interception layers are preloaded into each application as previously disclosed: App- 1   142  has its interception layer  143  preloaded, App- 2   144  has its interception layer  145  preloaded, and App- 3  has its interception layer  145  loaded. Similar to how individual processes within an application are handled, the three individual interception layers  143 ,  145 ,  147  comprise the application group&#39;s interception layer  148 . 
     As taught, the interception layer for an application and the interception layer for an application group work in a similar manner using the same preloaded shared library; hence there is no need to distinguish between the two. In the following, the nomenclature “Interception Layer” is used to designate the interception functionality across both applications and application groups. 
     The administrator  152  commits the application group to the IDB  150 . The IDB uses the same mechanisms as disclosed above for individual applications, and structures the isolated environment  154  so that the individual applications share resources and file system. By installing the applications together they automatically use the same isolated environment and sharing is fully automatic without requiring any additional information. The interception layer  148  intercepts, as previously disclosed, and requires no special configuration; all application group information is contained within the IDB  150  and the settings for the isolated environment  154 . 
     8. Concurrent Operation of Multiple Application Groups 
       FIG. 6  illustrates by way of example embodiment  160 , concurrent operation of three application groups: application group A  162 , application group B  166  and application group C  170 . Each application group consists of one or more applications. As previously disclosed each application group has a dedicated interception layer: IL  164  for application group A  162 , IL  168  for application group B  166 , and IL  172  for application group C  170 . Each interception layer  164 ,  168 ,  172  provide the interception services as previously disclosed, with each attached to only one application group. As previously disclosed, the Interception Database  174  is global, and is shared between all application groups and interception layers. 
     The administrator  176  commits all administrative settings to the IDB  174 , which is reflected in the database tables for the isolated environment  178 . 
     9. Running Multiple Concurrent Instances of One Application 
     At times it may be desirable to run multiple instances of the same application or application group, but in separate isolated environments. Referring again to  FIG. 6  for illustrative purposes. The administrator  176  defines each instance of the application group using separate application group names. Even though Application Group A  162 , Application Group B  166 , and Application Group C  170  are identical, they have been pre-defined with their own environment, and thus run in separate isolated environments without any further intervention or configuration. 
     10. Adding Checkpointing to the Isolated Environment 
     The Backensto and Havemose references cited above teach checkpointing of multi-process multi-threaded application groups on Windows and Linux respectively without an isolated environment. The general approach taken include:
         A public Barrier, generally implemented as a named semaphore   Full transparency requiring no changes to application or operating system,   Pre-loading of a checkpointing library into the address space of the individual processes,   Interception of key system functions, such as exec, fork, and access to system resources such as files,   Per-process dedicated checkpointing thread, and   Programmatic launch of all application group applications and processes through a coordinated Application Group Control Process (AGCP), called a “coordinator” in the two cited applications.       

     Checkpointing of application groups within the isolated environment is complicated by the addition of two new functional components: the interception layer (including the application process interception layers), and the interception database. Generally, the interception layer is contained within the application processes, while the interception database is external. The following teachings incorporate the cited checkpointing references into the present invention. 
     Application isolation utilizes interception to redirect resource access to the isolated environment. To provide checkpointing in the context of application isolation, the previously disclosed interception mechanism is enhanced to first pass all intercepted functions through the checkpointing library. The checkpointing library operates on the running program on the host operating system, and utilizes interception to capture fork( ), exec( ), memory operations and other resources as disclosed in the two cited references. This is followed by the interception handling for resource mapping related to the isolated environment as disclosed previously. 
     The checkpointing library is pre-loaded along with the interception layer into the address space of each application process. To keep multiple independent processes coordinated a new component is introduced: the Application Group Control Process (AGCP) responsible for launching the application group, preloading the libraries, initializing and starting the application group. In summary the following additional steps and components are added:
         The Application Group Control Process (AGCP) with responsibility for launching all applications within the application group, preloading all interception and checkpointing libraries   Processing of fork( )/exec( ) and resource interceptors and communication of process creation and resource allocations to AGCP   Automatic and transparent addition of a checkpointing thread to all running processes within all application groups being checkpointed.   Creation of a public checkpoint barrier by AGCP   Asynchronous triggering of checkpoints by AGCP       

     The AGCP furthermore assumes the full functionality of the loader and the custom symbol resolution as disclosed above. AGCP is responsible for all aspects of application launch, termination, installation of interception, loading of checkpointing library, and triggering of checkpointing. 
     In an embodiment on Linux and UNIX, AGCP triggers the asynchronous checkpoints using signals. In an embodiment on Window, Asynchronous Procedure Calls (APC) are used to trigger the checkpoints. 
       FIG. 11  illustrates by way of example embodiment  280  checkpointing of an application group  282 . By way of example, the application group  282  consists of one application A 1   286 . Multiple applications are handled in a similar manner. The Application Group Control Process (AGCP)  284  launches  285  Application A 1   286 . The AGCP  284  loads  304  the barrier  302  for the application group. As part of the load process, the AGCP  284  preloads the interceptors  288 , including the Interception Layer (IL)  300 , for each application process and the checkpointer library  289  for each application process. The application process interception layer  288  and the checkpointing library  289  are shared libraries and pre-loaded together. In an alternate implementation, the application process interception layer  288  and the checkpointing library  289  are combined into one shared library. Both libraries operate within the address space of the application process where they were loaded.  FIG. 11  illustrates by way of example an Application A 1   286  with one process and one corresponding application interception layer  288  and one checkpointing library  289 . Multiple processes are handled in a similar manner with each process having a corresponding application process interception layer and checkpointing library. As previously taught, the Interception Layer for an application is comprised of the individual application process interception layers. To distinguish between interception inside the application process interception layer  288  and the resource re-mapping functionality managed by the interception layer, the Interception Layer  300  is depicted on the diagrams. In the preferred implementation, the resource remapping functionality within IL  300  is embedded within the application process interception layer  288  and is executed after the checkpointing interceptors return  297  to the application process interception layer  288 . 
     As part of loading and initializing the application A 1 , AGCP  284  further creates a dedicated checkpointing thread for each process in the application group.  FIG. 11  illustrates by way of example a one-process application A 1  with one corresponding checkpointing thread  312 . Multi-process applications are handled in a similar manner with one checkpointing thread created per process. As processes are created and terminated, checkpointing threads are added and removed as necessary as disclosed in the two cited references. As part of initializing the checkpointing library  289 , the checkpointing library registers  306  the current process with the checkpoint barrier  302  The registration ensures that the current thread and process is included in the barrier, and ensures that the current process&#39; checkpoint thread  312  is called as part of the barrier 
     The Interception database IDB  301  is global to all application groups within the isolated environment. If the IDB  301  has not been loaded, the AGCP  284  launches the IDB  301  prior to the performing the load process disclosed above. 
     The checkpointer and the isolated environment both need access to all intercepted functions. In general, the checkpointer operates on the running application and utilizes interception to capture resource and their usage. The isolated environment utilizes the interception to re-direct resource usage to the isolated environment. By way of example, and not limitation, when application A 1   286  reaches function ifunc( )  293 , which is subject the interception, the previously disclosed control flow is adjusted to account for the presence and requirements of the checkpointer. The function ifunc( )  293  is intercepted  294  and re-directed to the application process interception library  288 . At this point ifunc( ), its context and parameters reflect the actual running application process. The intercepted call is first forwarded  296  to the checkpointing library  289 , where all relevant stack information is saved, as disclosed in the two cited references. If ifunc( ) changes the process hierarchy, the change is communicated  302  to AGCP  284  in order to have AGCP  284  preload or remove the interceptors as previously disclosed. Control is then returned  297  to the application process interception layer  288 . The application process interception layer calls  290  to the Interception Layer (IL)  300 . The IL  300  remaps resources using the Interception Database  301  as previously disclosed. Adjusted resources or data are returned  292  to the interceptor and sent back  295  to the calling application process via the return of ifunc( ). 
     11. Interception, Checkpointing, Data and Control Flow 
     In continuation of the example in section  5  above,  FIG. 12  illustrates by way of example embodiment  320  the data and control flow with checkpointing activated. By way of example the application group consists of one application  326  with one process. The Application Group Control Process  322  as previously disclosed, launches the application  326 , preloads the application process interception layer  330 , preloads the Interception Layer  338 , the checkpointing library  332 , and creates the checkpointing thread  328 . As disclosed the AGCP  322  also launches the Interception database  340  as necessary. 
     Continuing the example from section  5 :
         int main(void)       

     {
         char const *pStr=“small text”;   FILE *fp=fopen(“/home/user/newfile.txt”, “w”)   if (fp !=null)
           fwrite(pStr,strlen(pStr),1,fp);   
           fclose(fp)       

     } 
     The call to fopen( ) is intercepted by the application interception layer  330 , and passed to the checkpointing library  332 . The checkpoint library  332  captures the real resource name (“/home/user/newfile.txt”) and attributes (“w”), as disclosed in the two cited references, and the call returns to the application process interception layer  330  and forwarded to the Interception Layer  338 . The interception layer  338  then, as previously disclosed, translates using the IDB  340 , the public resource into the corresponding resource in the isolated environment  342 . The call to fopen( ) is finally forwarded  344  to the actual implementation in the system libraries  346  and operating system  348 . Return values  345  from fopen( ) is returned to the IL  338 , translated  340  back into the host environment as appropriate, forwarded  336  to the application process interception layer  330 , and ultimately returned to the calling application process  326 . The file pointer (FILE *fp) has been created in the host environment by the application  326 , intercepted for checkpointing with host-environment settings, and re-directed to the isolated environment by the IL  338  and IDB  340 . This ensures that the checkpointer works on the actual executing program, while resource access is redirected under both the application  326  and the checkpointer  332 . 
     The call to fopen( ) is followed by a call to fwrite( ) writing data to disk. Contrary to fopen( ), fwrite( ) operates on a file pointer, and appears host-native to the application and the checkpointer, but was translated by the isolated environment as just disclosed. The checkpointer intercepts the fopen( ) call, but does not need to do modify anything. Likewise, the interception for the isolated environment does not need to modify any of the parameters and lets the fwrite( ) simply write the data. 
     By way of example, and not limitation, the teachings so far describe two-layer interception: first interception by the application process interception layer followed by interception by the checkpointer. In general, any number of interceptions can be layered in a similar manner. Similarly, a hierarchy of interception is supported by traversing the hierarchy and each time passing arguments and results down and up the hierarchy, as disclosed for the two-layer interception. Most applications use multiple system libraries or other shared libraries all of which are loaded as part of the load process. As previously disclosed, the Application Group Control Process (AGCP) is responsible for loading the application group. The AGCP includes the operating system loader logic, and therefore has access to and knowledge of references to external libraries and is responsible for loading them. The AGCP automatically intercepts all functions in said libraries, building the interception hierarchy automatically without requiring any manual intervention. 
     12. Checkpointing an Application or Application Group within the Isolated Environment 
       FIG. 14  illustrates by way of example embodiment  380  checkpointing of application groups within an isolated environment. By way of example the application group consists of three applications: application A 1   386 , application A 2   388  and Application A 3   390 . Any number of applications is handled in a similar manner. Each application may be single process or multi-process. As previously taught in detail, the application group control process (AGCP)  382  loads  384  the barrier  387 , the individual applications A 1   386 , A 2   388  and A 3   390 . The AGCP also pre-loads the application process interception layer, checkpointing library, Interception layer for each application process, and creates the checkpointing thread for each application process. Finally the AGCP  382  loads the Interception database  392  if not already loaded. For each application process, the process, checkpointing thread and the pre-loaded libraries run within the address space of the process. 
     Checkpoints are taken in a synchronized manner across all application processes. The synchronization is accomplished using the checkpointing barrier  387 . The detailed teachings of checkpointing multi process application groups are provided in the Havemose and Backensto references previously cited. The general checkpointing process is
         Triggering of checkpointing  383  by AGCP  382  and activation of the barrier  387     Signaling  385  of each individual checkpointing thread to enter the barrier and halt its process and threads at the barrier   Checkpointing of all application processes and threads followed by checkpoints being written to local or remote disk   Upon completion, all application processes are released from the barrier.       

     The checkpoint includes all data within the address space of the application processes, including the application process interception layer, the interception layer and the checkpointing library. This ensures that any in-process interception or resource mapping is fully captured and included in the checkpoint. 
     By way of example, and not limitation: A 1  has intercepted an open( ) call, processed it in the application process interception layer and the checkpointing layer, and is in the middle of processing the resource mapping in the interception layer at the time the barrier is entered. With the entire address space included in the checkpoint, the exact state of all shared library data is captured, including the incomplete resource mappings. If at a later time a restore from checkpoint is issued, everything is brought back in the same state, including the incomplete resource mapping. 
     In a preferred embodiment, the application checkpoints are stored within the isolated environment. In an alternate embodiment, the application checkpoints are stored outside the environment in a shared location. 
     In a preferred embodiment, the Interception database  392  is not included in the checkpoints for the individual applications, but is runs as a separate entity. As part of the checkpointing barrier  387  a signal  395  is sent from the barrier to the interception database  392  to persistently store  393  the settings for the application group&#39;s isolated environment. 
     In an alternate implementation where only one application group uses the interception database  392 , the interception database is added to the application group, launched by the AGCP  382  and included in the barrier  387  and the checkpoints 
     13. Restoring Application Groups from Checkpoints 
     The teachings for restoring multi-process, multi-threaded application groups running without an isolated environment are disclosed in the Havemose and Backensto references cited above and included by reference. 
     The checkpoints for the application group contain all the process and thread hierarchy information, including all environmental information.  FIG. 14  also illustrates an example embodiment  380  of the key steps involved in restoring an application group from checkpoints. First the Application Group Control Process (AGCP)  382  is loaded. The AGCP  382  reads the process tables from the checkpoints and creates the process and thread hierarchy for the entire application group. For application A 1   386  the checkpoint is loaded from disk, the process hierarchy is overlaid with the checkpoint image, and the image is exec( )&#39;ed the number of times indicated in the checkpoint and environment. The AGCP  382  also pre-loads all necessary shared libraries, including but not limited to the application process interception layer, the interception layer, and the checkpointing library. The AGCP  382  repeats this for application A 2   388  and application A 3   390 . 
     All processes and threads within the application A 1   386 , A 2   388  and A 3   390  are halted at the barrier  387 , corresponding to checkpoint from which they are being restored. All threads and processes are then released from the barrier and the application group proceeds to run. 
     As the interception layer and the application process interception layer are included in the checkpoint, any in-process resource translation resumes at the exact point where the checkpointing occurred. This ensures consistency across checkpoint and restore. 
     In a preferred embodiment, the application checkpoints are stored within the isolated environment. When restoring, the checkpoint is available within the isolated environment. 
     In an alternate embodiment, the application checkpoints are stored outside the environment in a shared storage, typically on networked storage. When restoring, the checkpoint file is first retrieved from the shared storage then used to restore from. 
     In a preferred embodiment where the interception database  392  is external to the application group, the interception database  392  is reloaded with the settings for the isolated environment  393  while the application group is in the barrier. The settings for the isolated environment were persistently stored  393  as part of the checkpointing barrier. 
     In an alternate embodiment where the interception database is included in the application group, the interception database is restored along with the application group. 
     14. Checkpoint and Live Migration Triggers 
     Checkpointing and Live Migration can be triggered in a variety of ways. In general, the trigger can fire at any time and is, from the application group&#39;s perspective, therefore asynchronous. 
       FIG. 14  illustrates by way of example embodiment  380 , the checkpoint and live migration trigger module  383  within the application group control process  382 . While the trigger may be deterministic as far as the checkpoint triggers  383  is concerned, it arrives  385  asynchronously and asynchronously triggers entry into the barrier  387 . 
     Example triggers include but at not limited to:
         Time based trigger, such as ever 5 seconds or once daily   Environmentally based triggers such as
           CPU load being too high for some period of time   CPU temperature being too high for some period of time   Host running out of disk space   Host running out of memory   
           Configuration based trigger
           User&#39;s application quota exceeded on system   Application need resources not available on current host   
           User-driven triggers such as
           administrator issues a live migrate in preparation for a host reboot   administrator issues a live migrate in preparation for an application upgrade
 
While the actual trigger may vary, the underlying event mechanism is the same: The AGCP&#39;s  382  checkpoint trigger module  383  issues a checkpointing event  385  to the barrier  387 .
   
               

     15. Installation-Free Deployment 
     One of the major problems with application deployment is the actual installation and the associated risks as disclosed previously. Using the present invention, a pre-created isolated environment can be used in place of performing an actual installation. The isolated environment contains all application files, shared libraries, and installation data and can be moved, copied and run from anywhere the present invention is present. 
       FIG. 7  illustrates by way of example embodiment  180 , how to deploy an isolated environment without needing more than one initial installation  181 . First the administrator  196  installs  184  the application group  182 . As previously taught the interception database  186  creates an isolated environment  188  which contains all application group data, including shared files, data and programs. As taught above, the isolated environment is written to storage and can be copied and run elsewhere. With the isolated environment ensuring isolation from the underlying operating system and applications, an isolated environment can be deployed on a different node by copying the entire isolated environment directory structure to the new node and starting the application. Referring to  FIG. 7 , the administrator  196  copies the isolated environment  188  into the first node  190 , the second node  192  and the third node  194 . 
     In an alternate embodiment, the environment  188  is stored on shared storage, and is accessed directly from the shared storage. In this embodiment, the isolated environment is loaded directly from shared storage, and only local data, such as temporary files, are kept locally. 
     In another embodiment, the environment  188  is saved to storage and shipped to a remote site. The remote site loads the environment and runs the applications directly from within the environment without any installations. In this embodiment the present invention may be used for disaster recovery. 
     16. Live Migration of Application Groups within and Between Isolated Environments 
     Installation free deployment can be enhanced using the checkpointer to provide “live migration” of running application groups. A “Live Migration” is the process of moving a running application from one environment to another without restarting the application and losing session data. The isolated environment and checkpointing are configured such that the checkpoints are included within the isolated environment. A live migration of an application group is performed with the following steps:
         Checkpointing of the application group including saving the checkpoint within the isolated environment. The applications within the group are terminated just prior to exiting the checkpointing barrier (“checkpoint-terminate”).   Copy the isolated environment data to the destination system   Restore the application group from the checkpoints supplied within the isolated environment.       

     The restore from checkpoint can be activated within the same isolated environment, within a new isolated environment on the same host, or on a new isolated environment on a different host. 
     The net effect of checkpoint-terminate followed by a restore from checkpoint, is that the application execution is moved from one isolated environment to another without loss of data. There is no loss of application data, as the application is precluded from running between the checkpoint and the restore, and therefore has not executed any instructions. 
     17. Live Migration for Scale-Out 
     In a preferred embodiment, Live Migration may also be used for scale-out. In stead of terminating a just check pointed application group, said application group is left running while a second copy is created using the checkpoint on a new host. After creating the second application group using the modified live migrate, there are two running copies of the same application with identical configuration. Using a front-end load-balancer, incoming traffic is divided between the two application groups with each copy handling approximately half of all sessions. Inactive sessions generally automatically expire. 
     18. Administration 
       FIG. 8  illustrates by way of example embodiment  200 , the management infrastructure. The administrator  202  communicates configuration preferences to the Interception database  204  for each isolated environment  206 . The IDB  204  contains, as disclosed above, two separate modules: 1) a rules engine ( FIGS. 4 — 130 ) and 2) management of the resource mappings ( FIG. 4-132 ). The rules engine implements the administrator provided resource translations and populates the tables ( FIG. 4 — 134 , 136 , 138 ). 
     The administrator  202  provides general configuration information applicable to all isolated environments and applications  203 , unless explicitly changed for a particular isolated environment  205 . Examples of administrator-provided global configuration information  203  includes, but is not limited to
         Default storage location for all isolated environments   Default resource exceptions   Default application and application group naming   Default policy for installing fonts and shared resources into global or isolated environment   Default checkpointing policies including checkpointing frequency, and location of checkpoint storage   Default live migrate policies such as thresholds for CPU utilization, CPU heat, and storage utilization       

     Each setting can be changed, i.e. replaced, on an application by application basis, and on an application-group by application basis. As determined by the administrator, examples of administrator-provided application-level configuration information  205  include, but is not limited to
         Storage location for isolated environment   Logical name of application or application group   Application or application-group specific resource exceptions   Policy for installing fonts and shared resources into global or isolated environment   Checkpointing and live migrate policies       

     The combination of the global configuration information  203  with the rules engine ( FIG. 4 — 130 ), makes the configuration and deployment on new isolated environment fully automatic after the initial global configuration has been provided. As disclosed, it may be desirable to change one or more of an application&#39;s isolated environment settings. By way of example, and not limitation, if a particular application needs to locally access certain resources only available on a particular server, that one application&#39;s isolated environment would be located on that particular server, while all other environments were centrally stored. The ability to “mix and match” environments and deployments ensure full flexibility and ability to deploy multiple applications in a heterogeneous environment with all the benefits of the present invention. 
     In another embodiment the administrative functions  202  is done programmatically using an Application Programming Interface (API). 
     11. Deployment Scenarios 
       FIG. 9  illustrates by way of example embodiment  220  a variety of ways the invention can be configured to operate. In one embodiment, the invention is configured to run from a central file server  222 , in another it is configured to run on a pair of application servers  224 ,  226 . In a third embodiment the invention is configured to run on a LAN  228  connected PC  232  together with the application servers  224 ,  226 , and with environments loaded from the central file server  222 . In a fourth embodiment the invention is configured to isolate applications on a cell phone  230 , which is wirelessly connected  238  to the Internet  236 , the application servers  224 , 226  and the file server  222 . A fifth embodiment has an isolated environment on a home-PC  234  connected via the internet  236  to the application servers  224 , 226  and the LAN PC  232 . The invention runs on one or more of the devices, can be distributed across two or more of these elements, and allows for running the invention on any number of the devices ( 222 , 224 , 226 , 230 , 232 , 234 ) at the same time 
     12. Conclusion 
     In the embodiments described herein, an example programming environment was disclosed for which an embodiment of programming according to the invention was taught. It should be appreciated that the present invention can be implemented by one of ordinary skill in the art using different program organizations and structures, different data structures, and of course any desired naming conventions without departing from the teachings herein. In addition, the invention can be ported, or otherwise configured for, use across a wide-range of operating system environments. 
     Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the exemplary embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”