This section describes how Application Server Enterprise Edition software, BEA WebLogic Server, and IBM WebSphere® Application Server manage application server clustering. Application server clustering is a loosely coupled group of application servers that collaborate to provide shared access to the services that each server hosts. The cluster aims to balance resource requests, high availability of resources, and failover of application logic to provide scalability. Portal Server and Access Manager are not pure web applications. Instead, these applications are composed of local files residing on a machine and three web applications: portal, amserver, and psconsole. These three web applications run in a web application container, which runs in an application server web application container.
The Java Enterprise System installs and configures the local files, configures the local application server, then deploys the three WAR files on the local web application container. The WAR files themselves are not self-contained. The WAR files depend on the local files and directories on the machine to provide their service.
An application server cluster is a logical entity that groups many application server instances, potentially hosted on different machines. Pure web applications are deployed on a cluster using application server specific deployment tools. Once deployed on the cluster, the web applications are deployed to all the server instances that the cluster is made of, and managed in a central way.
Because of Portal Server’s dual nature, as a local application as well as a web application, install Portal Server on an application server using the following steps:
Install Portal Server on all machines using the same configuration settings.
Deploy the three web applications (portal, amserver, and psconsole) to the cluster.
The following sections explain what it means to enable Portal Server to run on an application server cluster.
The Sun Java System Application Server Enterprise Edition 8 provides a robust J2EE platform for the development, deployment, and management of enterprise applications. Key features include transaction management, performance, scalability, security, and integration. The Application Server supports services from Web publishing to enterprise-scale transaction processing.
The Application Server is available in the Platform and Enterprise editions. The Platform edition is free and is intended for software development and department-level production environments. Designed for mission-critical services and large-scale production environments, the Enterprise edition supports horizontal scalability and service continuity via a load balancer plug-in and cluster management. The Enterprise edition also supports session continuity via the Highly Available Database (HADB). See the following Application Server Enterprise Edition documentation for more information:
http://docs.sun.com/db/coll/1310
The BEA WebLogic Server product uses the following definitions:
Domain. An interrelated set of WebLogic Server resources managed as a unit. A domain includes one or more WebLogic Servers, and might include WebLogic Server clusters.
Administration Server. A WebLogic Server running the Administration Service. The Administration Service provides the central point of control for configuring and monitoring the entire domain. The Administration Server must be running to perform any management operation on that domain.
Managed Server. In a domain with multiple WebLogic Servers, only one server is the Administration Server; the other servers are called Managed Servers. Each WebLogic Managed Server obtains its configuration at startup from the Administration Server.
See the following documentation for more information:
http://edocs.beasys.com/wls/docs61/cluster/index.html
You start the Administration Server with the following command:
install_dir/config/domain_name/startWeblogic.sh
The local server takes its configuration from the install_dir/config/domain_name/config.xml file. To start a Managed Server, use the following command:
install_dir/config/domain_name/startManagedWebLogic.sh servername admin_server_url
Instead of taking its configuration from the install_dir/config/domain_name/config.xml local file, the Managed Server takes it from the Administration Server, using HTTP.
The default configuration supported for installing Portal Server on BEA WebLogic Server is a single server that is also the Administration Server for the domain.
A BEA cluster is a set of managed servers in the same domain, that are declared in the WebLogic console as a cluster. When deploying a web application, you use the name of the cluster, not the name of the individual servers. After the deployment, the web application is identically deployed to all machines in the cluster.
Session failover in BEA is described in the following document:
http://edocs.beasys.com/wls/docs61/cluster/servlet.html#1009453
Using in-memory replication for HTTP session states requires the following prerequisites:
Portal Server supports the use of WebLogic Server clusters with in-memory session replication. See the BEA documentation for instructions to set up these clusters. The Sun Java Enterprise System 2005Q5 Installation Guide documents the load balancer configuration for such a cluster using the HttpClusterServlet that ships with BEA. You can also set up other load balancing hardware and software documented by BEA in the same way.
Session data must be serializable.
Use the setAttribute to change the session state.
To install a BEA cluster, your BEA license for each machine participating in the cluster must be a special BEA cluster license. See the BEA documentation for the procedure to get the license and set up a BEA cluster with HttpClusterServlet.
The IBM WebSphere Application Server product uses the following definitions:
Administrative domain. The logical space in which the configurations for various objects in the WebSphere environment reside. Inside one administrative domain you start with an application server. This is the default installation.
Server group. A server group is a template for creating additional, nearly identical copies of an application server configuration. (This is the equivalent of BEA’s cluster.)
Clones. A copy of the server group, on the same machine or on different machines. Clones are the equivalent of BEA’s managed servers.
See the IBM WebSphere Application Server documentation for more information:
http://www-306.ibm.com/software/webservers/appserv
WebSphere Advanced Server provides a more robust approach to clustering because it includes a database. In Advanced Server, all servers use the database for the configuration information. You can use the WebSphere administration console, a Swing Java application, or the command-line utilities XMLConfig and wscpthen to manage the servers.