# Patent

## Title
Automated server replication

## Abstract

Methods and apparatus for detecting a change in demand for server resources across a load-bearing system having one or more content servers hosting identical content, the load-bearing system being connected to a network of content servers; and automatically modifying the number of content servers on the load-bearing system in response to the change in demand.

## Background
BACKGROUND
This invention relates to automated server replication.
The popularity of the World Wide Web as a communications medium lies in the richness of its information content and ease of use. Information in this medium exists as objects in a widely distributed collection of internetworked servers, each object uniquely addressable by its own Uniform Resource Locator (URL). The proliferation of commercial applications on the World Wide Web brings with it an increasing number of users making ever-increasing numbers of requests for web content. The problems of latency and bandwidth considerations manifest themselves in delay and lost information.
Network architects respond using an array of solutions, one of which is the server farm. This involves the use of multiple web servers with identical content, or the segmentation based upon functionality. For example, two servers for web functions, two for File Transfer Protocol (FTP), two as a database, and so forth. The use of multiple servers solves one problem at the expense of creating another. If there are multiple servers, how does the end user locate a particular web site? Presently, names and Universal Resource Locator (URLs) are resolved into unique single addresses by a Domain Name Service (DNS) residing in a DNS server. DNS servers maintain a list of domain names cross referenced to individual Internet Protocol (IP) addresses. However, if multiple web servers or server farms are used, a modified version of DNS service is used. A common approach to this problem is to modify the DNS system to be aware of a one-to-many mapping of names-to-IP-addresses. Thus, the DNS will return an IP address that comes from a list of possible IP addresses that correspond to a particular web object. Thus, from one moment to the next, a DNS query will resolve to different IP addresses. In this example, the modified DNS decides which IP address to return based on how busy each of the servers is.
In current network management systems, there are various methods of detecting and monitoring the load across a server or a server farm. One system uses a load capacity detection agent to monitor the load across a server or a server farm. In this system, when the load detection agent detects that a server farm, for example, is experiencing excess load, the agent notifies a system administrator of the system. The system administrator may decide to manually take action to either reduce the load across the server farm, or alternatively, increase the available load capacity by adding a server to the server farm. Generally, the system administrator adds a server by manually identifying an additional available server, and then modifying the entries in the load management system to include the IP address of the recently-added content server.
SUMMARY
In general, in one aspect, the invention provides a method and apparatus, including a computer program apparatus, implementing techniques for detecting a change in demand for server resources across a load-bearing system having one or more content servers hosting identical content, the load-bearing system being connected to a network of content servers; and automatically modifying the number of content servers on the load-bearing system in response to the change in demand.
Each content server on the network may be categorized as active or idle. The hosted content may be assigned a priority level, and a number defining a maximum number of content servers on the load-bearing system. A content server may be added to the load-bearing system if the change in demand is greater than a pre-configured threshold and the number of content servers on the load-bearing system is less than a maximum number assigned to the hosted content. The number of content servers may be modified by selecting an available content server on the network; loading hosted content onto the selected content server; and adding the selected content server to the load-bearing system. All of the content servers on the load-bearing system including the selected content server host identical content. The available content server having the lowest priority level, the highest available load capacity, or the least number of active sessions may be selected.
The hosted content may be assigned a number defining a minimum number of content servers on the load-bearing system. A content server may be removed from the load-bearing system if the change in demand is greater than a pre-configured threshold and the number of content servers on the load-bearing system is greater than a minimum number assigned to the hosted content. The content server having the highest available load capacity or the least number of active sessions may be removed.
Embodiments may have one or more of the following advantages. The invention uses scripting, or other software techniques, to automate the addition or removal of a content server from a load-bearing system. Automating the addition and removal of content servers gives, for example, a web hosting operation a way to manipulate server resources between high-activity servers and low-activity servers without requiring any user intervention. In particular, the invention serves the needs of “seasonal” or “spiky” web applications, such as tax preparation services or Superbowl-related web sites, which experience a tremendous increase in the number of hits at specific times of the year.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.



DESCRIPTION OF DRAWINGS
FIGS. 1a-1d are block diagrams illustrating an internetwork topology including an network of content servers and a management server.
FIG. 2 is a flowchart of a process for automatically modifying the number of content servers on a load-bearing system.
Like reference symbols in the various drawings indicate like elements.



DETAILED DESCRIPTION
Referring to FIGS. 1a-1d, an exemplary internetwork 100 includes a network of servers 102 connected to a network of clients 104 through the Internet 106. The network of servers 102 includes a management server 108 and a group of content servers 110.
The content servers 110 are nodes on the network 102 that perform the actual serving of content, for example, Web pages or FTP files. Although only nine content servers 110 are shown in FIGS. 1a through 1d, it will be understood that any number of content servers may be connected to the network 102. Each content server 110 is capable of receiving queries from clients, doing substantially all the processing necessary to formulate responses to the queries, and providing these responses to the clients. Web servers, for example, respond to requests from clients (e.g., through browser software) for access to files and data. Other types of servers allow clients to share access to network devices, such as shared printers or disk storage.
In one exemplary commercial setting, each content server 110 is a managed node on the network 102 maintained by a network operator, such as Genuity Inc. of Woburn, Mass. By the term “managed node”, it is meant that each content server 110 runs a management process that allows another computer to query the managed node for information. For example, Simple Network Management Protocol (SNMP) describes how a computer formats a message to send to the managed node. Software on the managed node, called an SNMP agent (not shown), examines SNMP messages it receives, and responds accordingly. Each SNMP agent maintains a local database of variables that describe the state of the content server 110 and may, optionally, affect its operation. Each SNMP agent's local database includes, but need not be limited to the following: the number of packets and bytes sent and received from the Internet 106, the number of broadcasts, the current output queue size, the current transaction rate, the current processor utilization, and the current disk utilization.
Content servers 110 are the systems which store information that may be accessed using web browser software such as Netscape Communicator® and Microsoft's Internet Explorer®. Content servers transmit their information in response to receiving a message of a format specified by Hyper Text Transfer Protocol (HTTP). The format of the server's response is also specified by HTTP, and is understood by web browser software.
Network management on the network 102 can be done from management servers, an example of which is shown as management server 108, which are general-purpose computers running management software. The management server 108 interacts with the SNMP agents in the content servers 110 using the SNMP protocol. This protocol allows the management server 108 to query the state of an agent's local variables, and change them if necessary. For example, the management server 108 can issue commands and get responses that allow the management server 108 to monitor the resources available (i.e., available load capacity) on each content server 110, and express them in a way that enables the content servers 110 to be categorized as active or idle. In one example, the management server 108 only considers the CPU resource, and neglects all others. In other implementations, the management server 108 uses a more complex combination of considerations, with load metrics ranging from the instantaneous CPU utilization and IO queue length, through to a linear combination of CPU, memory and IO queue lengths. The management server 108 can also modify network routing tables, and change the status of network links and devices. The collection of all possible variables available via SNMP is given in a data structure called the Management Information Base (MIB), which is formally defined in the Internet Engineering Task Force (IETF) Request For Comment (RFC) 1213. The IETF is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and smooth operation of the Internet—it is open to any individual.
The management server 108 also houses several other software components, which include in one implementation, an image manager 116, and a content storage system 118. In the illustrated examples on FIGS. 1a-1d, a single server implements the software components of the management server 108. However, it should be noted that two or more servers connected to the network 102 may implement the software components.
The router 114 uses any one of a number of dynamic routing algorithms (e.g., distance vector routing and link state routing) to decide where to send packets addressed to a particular IP address; for example, how to get to a particular content server which are all distinguished based on their assigned IP address. Dynamic routing algorithms change their routing decisions in response to changes in the topology of the network 102. A set of files is stored in the content storage system 118. Each file contains content data, applications and all the necessary software required to implement a web site presence on the Internet 106. Each file can be loaded onto a content server 110 by the image manager 116. In one implementation, the image manager 116 maintains a table (shown below) that includes, for each file, a priority level, a minimum number and a maximum number of content servers 110 that can be used to implement the web site. The priority level indicates to the management server 108 the relative importance—to the network operator, Genuity Inc., for example—of implementating a particular web site in situations in which several web sites are vying for limited server capacity. In one implementation, a five-point scale is used to designate a priority level: “highest”, “high”, “medium”, “low” and “lowest”. Generally, the higher the priority level assigned to a file, the more server resources (up to the maximum number of content servers 110 identified in the table) are allocated to implement the web site. By default, content servers 110 that are idle are assigned a “lowest” priority level. When a file having a “highest” priority level is loaded onto a content server 110 that is idle, for example, the priority level of the content server 110 changes from “lowest” to “highest”.
Assume, for example, that three files—file “A”, file “B”, and file “C”—are stored in the content storage system 118. The second, third and fourth table entries are populated with the following data:
















File
Priority Level
Min. Number
Max. Number





















A
highest
1
7



B
medium
1
3



C
low
1
3










Initially, each file is loaded and run on one or more content servers 110, indicated in dashed lines in FIG. 1a as load-bearing system A 120, load-bearing system B 122, and load-bearing system C 124. If a load-bearing system, such as load-bearing system A 120, has multiple content servers 110, the load on the system is distributed using one of the following schemes: (1) a load-sharing scheme; (2) a load-balancing scheme; or (3) a load-leveling scheme. Generally, content servers 110 in a load-sharing system that utilizes the load-sharing scheme are viewed in binary. That is, the server is either idle or busy, and load may only be placed on idle servers. Load-balancing schemes attempt to ensure that the load on each content server 110 in the system is within a small degree of the load present on every other content server in the system. Load-leveling schemes can be viewed as the middle ground between the load-sharing and load-balancing schemes. Rather than trying to obtain an even distribution across the system, or utilizing only the content servers 110 that are idle, the load-leveling scheme distributes load in a manner that minimizes congestion.

Referring to FIG. 2, a process 200 residing in the management server 108 periodically checks (202) the available load capacity on each load-bearing system. In one implementation, the process 200 polls each content server 110 in a load-bearing system to determine its available load capacity.
If the process 200 detects (204) that the load on the load-bearing system B 122, for example, is greater than a preconfigured threshold level (i.e., there is insufficient aggregate available load capacity), the process then determines (206) whether the number of content servers 110 in the load-bearing system B 122 is less than the maximum number that may be allocated to that system. If so, the process 200 will add a content server 110 to the load-bearing system B 122 if one is available. By use of the term “available”, it is meant that the content server 110 is idle and may be added to a load-bearing system, or alternatively, the content server has a lower priority level and may be removed from a particular load-bearing system and allocated to a different load-bearing system. For example, as shown in FIG. 1b, if the load-bearing system C 124 is implemented by a single content server 124a, the content server 124a is not available for re-allocation to either of the other two load-bearing systems 120 and 122, because the network operator has designated in the table that at least one content server 110 in the network 102 must be allocated to the load-bearing system C 124.
The process 200 first polls all of the content servers 110 on the network 102 to determine (210) if there is an available content server 110 on the network 102. If none of the content servers 110 are available, the process 200 logs and signals the event (208) to the network operator maintaining the network 102. Otherwise, the process 200 selects (212) one of the available content servers for addition to the load-bearing system B 122. If there are multiple available content servers 110, the process 200 will typically select one that is idle for addition to the load-bearing system B 122. However, if all of the available content servers 110 on the network 102 are active, as shown in FIG. 1c, the process 200 makes the selection as follows:

    
    
        (1) If there is only one available content server 110, the process 200 selects that content server 110.
        (2) If there are multiple available content servers 110, the process 200 selects the content server 110 having the lowest priority level.
        (3) If there are multiple available content servers 110 having the lowest priority level, the process 200 polls each of those content servers 110 to determine which content server 110 has the highest available load capacity and selects that content server 110. Alternatively, the process 200 polls each of those content servers 110 to determine which content server 110 has the least number of running processes in progress (called “active sessions”) and selects that content server 110.
    
    


Once the selection is made, say, for example, the process 200 selects the content server having an IP address of “128.11.234.59” 124b in the load-bearing system C 124, as shown in FIG. 1c, the process 200 can be configured to immediately stop all future client queries directed to the load-bearing system C 124 from being sent to the selected content server 124b for processing. The process 200 can also be configured to wait until all of the active sessions on the selected content server 124b have been terminated before removing that content server 124b from the load-bearing system C 124. Once removed, the process 200 retrieves the file “B” from the content storage system 118 and uses the image manager 116 to load (214) it onto the selected content server 124b. Referring to FIG. 1d, the process 200 then starts the selected content server 124b having the recently-loaded file “B”, and modifies the DNS system to add (216) the content server having an IP address of “128.11.234.59” 124b to the load-bearing system B 122. Thereafter, when a client requests a service by entering in a web browser the URL for the web site implemented by the load-bearing system B 122, the request can be directed to the content server 124b. 
Referring to FIG. 1c, 1f the process 200 detects (218) that the load on the load-bearing system B 122, for example, is less than a preconfigured threshold level, the process 200 then determines (220) whether the number of content servers 110 in the load-bearing system B 122 is more than the minimum number that may be allocated to that system 122. If so, the process 200 may select (222) a content server 110 from the load-bearing system B 122 for removal if the aggregate available load capacity of the load-bearing system B, the historical demand for services implemented by the load-bearing system B, as well as damping considerations, among others, warrants removal of a content server. The process 200 selects a content server for removal much in the same manner described above. That is, the selection may be made by polling each of the content servers 110 in the load-bearing system B 122 to determine which content server 110 has the highest available load capacity and selecting that content server 110. Alternatively, the selection may be made by polling each of those content servers 110 to determine which content server 110 has the least number of active sessions and selecting that content server 110. The process 200 can be configured to wait until all of the active sessions on the selected content server 110 have been terminated before removing (224) that content server 110 from the load-bearing system B 122, and categorizing it as idle.
Other embodiments are within the scope of the following claims.

## Claims

1. A computer implemented method comprising:
detecting a change in demand for server resources across a load-bearing system having a number of content servers hosting identical content, the load-bearing system being connected to a network of content servers, wherein the network comprises at least one other load-bearing system having one or more content servers each assigned a priority level; and
automatically modifying the number of content servers on the load-bearing system in response to the change in demand, wherein automatically modifying the number of content servers on the load-bearing system comprises:
selecting an available content server from a selected one of the at least one other load-bearing system based on a comparison of the priority level assigned to the available content server relative to at least one other content server in the network;
loading identical content onto the selected content server by an image manager in communication with the selected content server;
adding the selected content server to the load-bearing system, wherein all of the content servers on the load-bearing system including the selected content server use the identical hosted content;
detecting a change in demand greater than a pre-configured threshold; and
adding a content server to the load-bearing system if the number of content servers on the load-bearing system is less than a maximum number assigned to the hosted identical content,
wherein the hosted identical content is assigned a priority level of a plurality of priority levels, and wherein selecting an available content server comprises selecting an available content server having a lowest priority level and a highest available load capacity.

2. The method of claim 1, wherein each content server on the network is categorized as active or idle.

3. The method of claim 1, wherein the hosted identical content is assigned a number defining a maximum number of content sewers on the load-bearing system.

4. The method of claim 1, wherein the available content server having a least number of active sessions of the number of content servers is selected.

5. The method of claim 1, wherein the hosted identical content is assigned a number defining a minimum number of content servers on the load-bearing system.

6. The method of claim 1, further comprising:
detecting a negative change in demand greater than a pre-configured threshold; and
removing a content server from the load-bearing system if the number of content servers on the load-bearing system is greater than a minimum number assigned to the hosted identical content.

7. The method of claim 6, wherein removing comprises removing the content server having a highest available load capacity.

8. The method of claim 6, wherein removing comprises removing the content server having a least number of active sessions.

9. A system comprising:
a first network having client servers connected to an Internet;
a second network connected to the Internet, the second network comprising:
content servers connected to a management server, a first subset of the content servers providing a load bearing system, the management server including a means for detecting a change in demand for content server resources across the load-bearing system; and
means for automatically modifying a number of content servers in the first subset of content servers on the load bearing system in response to the change in demand, wherein automatically modifying the number of content servers on the load-bearing system comprises:
selecting an available content server on the Internet;
loading identical content from a management server onto the selected content server by an image manager in communication with the selected content server;
adding the selected content server to the load-bearing system, wherein all of the content servers on the load-bearing system including the selected content server use the identical hosted contents;
detecting a change in demand greater than a pre-configured threshold; and
adding a content server to the load-bearing system if the number of content servers on the load-bearing system is less than a maximum number assigned to the identical hosted content,
wherein the identical hosted content is assigned a priority level of a plurality of priority levels, and wherein selecting an available content server comprises selecting an available content server having a lowest priority level and a highest available load capacity.

10. The system of claim 9, wherein the first subset of content servers uses an identical hosted content.

11. The system of claim 9, wherein the management server includes a means for categorizing each content server as active or idle.

12. The system of claim 9, wherein the management server includes a means for assigning the priority level of the plurality of priority levels to the hosted content.

13. The system of claim 9, wherein the management server includes a means for assigning a number defining the maximum number of content servers on the load-bearing system to the identical hosted content.

14. The system of claim 9, wherein the management server selects the available content server having a least number of active sessions.

15. The system of claim 9, wherein the management server includes a means for assigning a number defining a minimum number of content servers on the load-bearing system to the identical hosted content.

16. The system, of claim 9, wherein the management system further comprises a means for:
detecting a negative change in demand greater than another pre-configured threshold; and
removing a content server from the load-bearing system if the number of content servers on the load-bearing system is greater than a minimum number assigned to the hosted content.

17. The system of claim 16, wherein the management server removes the content server having a highest available load capacity.

18. The system of claim 16, wherein the management server removes the content server having a least number of active sessions.

19. A system comprising:
a network comprising a plurality of content servers,
a plurality of load-bearing systems, wherein each of the load-bearing systems comprises one or more of the plurality of content servers; and
a management server configured to:
identify a load-bearing system with insufficient load capacity,
identify an available content server from one or more idle servers not already allocated to any of the load-bearing systems,
allocate the identified content server to the load-bearing system with insufficient capacity,
cause content to be copied onto the identified content server, wherein the content is identical to content associated with the load-bearing system with insufficient capacity,
detect a change in demand greater than a pre-configured threshold; and
add a content server to the load-bearing system if the number of content servers on the load-bearing system is less than a maximum number assigned to the hosted identical content,
wherein the identical content is assigned a priority level of a plurality of priority levels, and wherein identifying an available content server comprises identifying an available content server having a lowest priority level and a highest available load capacity.

20. The system of claim 19, wherein the management server is further configured to identify an available content server from a plurality of idle content servers already allocated to one of the other load-bearing systems by analyzing priority levels assigned to the plurality of idle content servers.

21. The system of claim 19, wherein each of the plurality of load-bearing systems distributes incoming content requests to associated servers based on a load scheme selected from a group consisting of a load-bearing scheme, a load-balancing scheme, and a load-leveling scheme.

22. The system of claim 19, wherein a notification is sent to a network operator maintaining the network if no content servers are available to be associated with the load-bearing system with insufficient capacity.

23. The system of claim 20, wherein the management server is further configured to identify an available content server allocated with one of the other load-bearing systems by polling each of the plurality of content servers to determine which content server has the highest available load capacity.

24. The system of claim 20, wherein the management server is further configured to identify an available content server associated with one of the other load-bearing systems by polling each of the plurality of content servers to determine which content server has the least number of running processes.

25. The system of claim 19, wherein each of the plurality of load-bearing systems is assigned a minimum number of content servers.

26. The system of claim 25, wherein the minimum number of content servers is assigned based on a priority level of the load-bearing system.

27. The system of claim 19, further comprising an image manager configured to de-allocate a content server from one of the load-bearing systems if the historical demand for service warrants de-allocation of a content server.

28. A method for allocating a number of servers to a plurality of web sites, the method comprising:
allocating one or more servers to each of a plurality of web sites;
for each web site, loading a file having content for implementing the web site onto the one or more servers allocated to the web site;
assigning a priority to each file;
monitoring load capacity on the one or more servers allocated to each web site;
detecting load at the one or more servers allocated to a web site that is greater than a specified threshold;
identifying a server allocated to one of the other web sites that is available to be re-allocated to the web site for which load is detected to be greater than the specified threshold, wherein identifying the server to be re-allocated comprises:
determining whether the file of a server allocated to another of the web sites is assigned a lower priority than the priority assigned to the file loaded on the one or more serves for which load is detected to be greater than the specified threshold; and
determining whether the number of servers allocated to the other web site is greater than a specified minimum number of servers;

if the file of the identified server has a lower priority and the number of servers allocated to the other web site is greater than the specified minimum number of servers, re-allocating the identified server from the web site to the web site for which load is detected to be greater than the specified threshold, wherein re-allocating the identified server comprises:
stopping directing of client requests to the identified server;
loading the file implementing the web site for which load is detected to be greater than the specified threshold onto the identified server; and
changing an Internet protocol address of the identified server to an IP address corresponding to the web site that the identified server is re-allocated to.

29. A computer implemented method comprising:
detecting a change in demand for server resources across a load-bearing system having a number of content servers hosting identical content, the load-bearing system being connected to a network of content servers, wherein the network comprises at least one other load-bearing system having one or more content servers each assigned a priority level; and
automatically modifying the number of content servers on the load-bearing system in response to the change in demand, wherein automatically modifying the number of content servers on the load-bearing system comprises:
selecting an available content server from a selected one of the at least one other load-bearing system based on a comparison of the priority level assigned to the available content server relative to at least one other content server in the network;
loading identical content onto the selected content server by an image manager in communication with the selected content server;
adding the selected content server to the load-bearing system, wherein all of the content servers on the load-bearing system including the selected content server use the identical hosted content;
detecting a change in demand greater than a pre-configured threshold; and
adding a content server to the load-bearing system if the number of content servers on the load-bearing system is less than a maximum number assigned to the hosted identical content,
wherein the hosted identical content is assigned a priority level of a plurality of priority levels, and wherein selecting an available content server comprises selecting an available content server having a lowest priority level and wherein the available content server having a least number of active sessions of the number of content servers is selected.

30. A system comprising:
a first network having client servers connected to an Internet;
a second network connected to the Internet, the second network comprising:
content servers connected to a management server, a first subset of the content servers providing a load bearing system, the management server including a means for detecting a change in demand for content server resources across the load-bearing system; and
means for automatically modifying a number of content servers in the first subset of content servers on the load bearing system in response to the change in demand, wherein automatically modifying the number of content servers on the load-bearing system comprises:
selecting an available content server on the Internet;
loading identical content from a management server onto the selected content server by an image manager in communication with the selected content server;
adding the selected content server to the load-bearing system, wherein all of the content servers on the load-bearing system including the selected content server use the identical hosted content;
detecting a change in demand greater than a pre-configured threshold; and
adding a content server to the load-bearing system if the number of content servers on the load-bearing system is less than a maximum number assigned to the hosted identical content,
wherein the hosted identical content is assigned a priority level of a plurality of priority levels, arid wherein selecting an available content server comprises selecting an available content server having a lowest priority level and wherein the management server selects the available content server having a least number of active sessions.

31. A system comprising:
a network comprising a plurality of content servers,
a plurality of load-bearing systems, wherein each of the load-bearing systems comprises one or more of the plurality of content servers; and
a management server configured to:
identify a load-bearing system with insufficient load capacity,
identify an available content server from one or more idle servers not already allocated to any of the load-bearing systems,
allocate the identified content server to the load-bearing system with insufficient capacity,
cause content to be copied onto the identified content server, wherein the content is identical to content associated with the load-bearing system with insufficient capacity,
detect a change in demand greater than a pre-configured threshold; and
add a content server to the load-bearing system if the number of content servers on the load-bearing system is less than a maximum number assigned to the hosted identical content,
wherein the identical content is assigned a priority level of a plurality of priority levels, and wherein identifying an available content server comprises identifying an available content server having a lowest priority level and wherein the available content server having a least number of active sessions of the number of content servers is selected.