WebSphere Application Server, Version 5.0 and virtualization

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WebSphere Application Server Network Deployment, Version 5.0 can help reap the benefits of a virtualization environment. IBM has enhanced existing capabilities and added new features to WebSphere Application Server, Version 5.0, making it easier for an enterprise to optimize resource use and management while maintaining system reliability and availability, and containing the costs of system administration. The key features that offer the ability to architect for a virtualized environment are discussed in subsequent sections.

In addition to the features discussed in this document, IBM WebSphere Application Server, Version 5 offers a wide range of features for a world-class application server. See www.ibm.com/software/webservers/appserv/infocenter.html for additional information.

WebSphere Application Server Network Deployment

Network Deployment can support a network of computer systems that is configured to run collaborating instances of the base application server installation. It provides centralized administration and workload management for a set of nodes, referred to as a cell.

A cell has a master administrative repository that stores the configuration data for the nodes in the cell. There is one deployment manager for each cell.

A deployment manager is an administrative agent that hosts the administrative program. The administrative program provides a single, central point of administrative control for all elements of the WebSphere Application Server distributed cell; it also manages clusters and workload balancing of application servers across one or several nodes.

A node is a logical grouping of managed servers that are instances of a WebSphere Application Server JVM, running in their own processes. A node contains many servers, but cannot span multiple computer systems. A single computer system can have multiple nodes installed, each with multiple managed servers. Each node contains a node level administrative repository that includes the configuration data of the cell and the local node.

A node agent manages all application servers on a node. Each node has a node agent that serves as an intermediary between the application servers on the node and the deployment manager that oversees the entire cell. A node agent is purely an administrative agent and is not involved in application serving functions. A node agent also hosts other important administrative functions such as file transfer services, configuration, synchronization, and performance monitoring

An application server is a WebSphere Application Server JVM process that hosts user J2EE applications.

Figure 2-4 depicts a sample network deployment cell.

Figure 2-4: WebSphere network deployment - cell environment

Clustering

The clustering technology in WebSphere Application Server, Version 5 supports high availability and scalability in a shared application server environment.

A cluster is a logical representation of the application servers. WebSphere Application Server, Version 5 provides vertical and horizontal clustering capability to prevent any given application server process from becoming a single point of failure. Vertical clustering refers to the configuration where application servers participating in a cluster are on the same machine. Horizontal clustering is made up of application servers on different machines. Vertical clustering is used to improve process availability and/or improve resource use on a single machine. Horizontal clustering eliminates any machine as a single point of failure. Figure 2-5 depicts sample configurations of vertical and horizontal clustering of application servers.

Figure 2-5: Vertical and horizontal clustering of application servers

IBM WebSphere Application Server, Version 5 now supports horizontal clustering across different platforms and operating systems. This is an important new feature for a shared application server environment.

Workload management

The objective of workload management (WLM) in WebSphere Application Server, Version 5 is to support load balancing and failover capabilities. WLM technology allows enterprises to configure, prioritize, and use all available resources to optimally service incoming requests. These features are essential in maintaining application server performance in an enterprise, especially when the resource use of applications varies.

Workload management can be implemented at three places in the execution path of WebSphere Application Server, Version 5:

1. A load balancer can route HTTP requests to a cluster of Web servers

2. A Web server can route HTTP requests to a cluster of WebSphere Application Servers - workload management at the Web container

3. A WebSphere Application Server or a Java client can route IIOP requests to a cluster of WebSphere Application Servers

This section discusses the second option, the use of HTTP workload management to implement the sharing of application server resources. HTTP WLM sprays requests to a cluster of Web containers (servlet engines). This type of load management provides clustering, failover and high-availability for the Web container tier. WebSphere Application Server, Version 5 interacts with traditional Web servers such as Apache, IBM HTTP Server, Sun iPlanet, Lotus Domino, and Microsoft Internet Information Services (IIS) using the native Web server plug-in architecture. The WebSphere plug-in interacts with the Web containers through the internal HTTP transports. Because workload management of HTTP requests is implemented in the plug-in, load balancing is available for HTTP requests that enter into the WebSphere Application Server, Version 5 domain through an external HTTP server.

HTTP WLM uses a weighted routing algorithm. This algorithm allows enterprises to assign weights to each cluster member server and have requests distributed to those servers based on the assigned weight. Over time, the proportion of the requests that are directed to any single cluster member is the weight of that server divided by the sum of the weights of all of the servers in the cluster. The weighted routing algorithm can also be used to stop new requests from being routed to a particular cluster member by setting the weight of that particular cluster member server to zero. When the weight of a member cluster server is zero, HTTP WLM does not route any new user request to this member. User requests with existing sessions are still sent to the member server. This is an important feature that can be used to remove an application server from a running environment with minimum interruptions to users.

In addition, HTTP WLM provides two-level failover support. Servers can be partitioned into a primary server group and a backup server group. The backup server group serves as standby available resources. The HTTP plug-in does not route requests to any server in the backup group as long as there are servers available in the primary group. When no servers in the primary group are available, the plug-in routes the traffic to the first available server in the backup group, or moves the request to the next available server in the backup group. The plug-in uses this server exclusively, as long as it is available. The two-level failover mechanism provides more robust failover support, allowing enterprises to plan for server over capacity, for example during high load spikes.

Administrative model

WebSphere Application Server, Version 5 provides a new infrastructure for managing and administering servers and applications. An open standards-based management framework, Java™ Management Extensions (JMX) is at the core of the Version 5 management capabilities. New administration tool sets built for Version 5 take advantage of this framework. More importantly, because all administrative operations are built based on the JMX framework, it is possible to tap into this framework to build custom administrative programs.

WebSphere Application Server, Version 5's administrative tool sets include: administrative console, the WebSphere administrative (wsadmin) scripting program, and command line tools.

• The administrative console is a Web-based graphic interface that provides many features for deployment and systems administration tasks. The administration console is extremely useful for exploring the available management options.

• The administrative scripting program wsadmin is a built-in, powerful, nongraphic command interpreter that enables the execution of administrative operations with scripting. This tool uses the bean-scripting framework (BSF), which supports a variety of scripting languages. The initial WebSphere Application Server release only supports the Tcl scripting language. Additional scripting language support will be available in future product updates. wsadmin is intended for production environments and unattended operations.

• Command line tools are simple programs that can be run from an operating system command line prompt to perform specific tasks, as opposed to general-purpose administration. Command line tools can be used for such tasks as to start and stop application servers, check server status, add or remove nodes, and so on.

In addition to these tool sets, WebSphere Application Server, Version 5 also provides a Java programming API for developing administrative programs. The administrative tools supplied with WebSphere Application Server, Version 5 are written according to the API, which is based on the industry standard Java Management Extensions (JMX) specification.

The combination of wsadmin along with the possibility of building custom administration functions provides powerful capabilities for WebSphere Application Server, Version 5 to significantly reduce the cost of supporting and managing an environment of dynamic resource sharing.

Coexistence

Coexistence, as it applies to WebSphere Application Server products, is the ability of multiple installations of WebSphere Application Server to run on the same machine at the same time. Multiple installations include multiple versions and multiple instances of one version. This means that multiple versions of WebSphere Application Server can now run on the same machine at the same time. This is especially useful for rolling out interim fixes or new versions of WebSphere Application Server onto production environment in an orderly way.

Coexistence makes possible software migrations on a shared hosting environment from one WebSphere Application Server version to another without the use of extra hardware. Coexistence combined with workload management enables software migration within an existing environment without causing significant service interruptions.

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