Cluster Configuration in weblogic

Setting Up, Configuring, and Using an Oracle WebLogic Server Cluster

Learn to take advantage of multiple Oracle WebLogic Server instances grouped into a cluster to maximize scalability and availability.

The key characteristics of a successful online system today include high availability, reliability, and scalability. Put simply, your online system must be ready to process a user request quickly and at any time, even when the number of requests grows abruptly. Strictly speaking, a growing number of user requests is a good thing, because that makes it clear that your online business is booming and opening up new opportunities for you. The ability to act on opportunities is a key characteristic of many successful businesses today.

To meet the requirements for greater availability and scalability, more and more companies are moving toward clustered infrastructures for their online solutions. Oracle WebLogic Server supports clustering, allowing an Oracle WebLogic Server cluster to be composed of multiple Oracle WebLogic Server instances running on different servers at the same time, so that application deployed to the cluster can take advantage of the combined processing power of multiple servers, failover, and load balancing.

To end users and applications, multiple Oracle WebLogic Server instances grouped into a cluster appear as a single Oracle WebLogic Server instance. But beneath the surface, the cluster uses an infrastructure that enables interconnecting clustered Oracle WebLogic Server instances to make them work as a single unit. It's important to realize, though, that setting up and using that infrastructure involves some configuration work on the part of a cluster administrator.

Key Benefits of Clustering

The idea behind clustering is pretty simple: Multiple server instances are grouped to work together to achieve increased scalability and reliability. In particular, the benefits of an Oracle WebLogic Server cluster include the following:

·         High availability—You can deploy your applications on multiple server instances within an Oracle WebLogic Server cluster. In this case, if a server instance that is running your application fails, application processing will continue (transparently to the application users) on another instance.

·         Scalability—New server instances can be dynamically added to a cluster to match consumer demand, without interrupting application processing.

·         Improved performance—Another advantage to deploying on multiple server instances in a cluster is that it provides several alternatives for application processing. The load balancing mechanism that clustering enables can significantly improve performance of your clustered application due to the efficient distribution of jobs and communications across the resources within the cluster.

To provide the benefits above, an Oracle WebLogic Server cluster supports the following features:

·         Load balancing

·         Application failover

·         Migration of a server instance

To grasp how things work in an Oracle WebLogic Server cluster, however, you first need to get at least a cursory understanding of how server instances interact with one another in a cluster and what mechanisms enable the deployment of an application on multiple server instances. The next section covers these topics, providing a brief overview of the Oracle WebLogic Server cluster technology.

How Clustering Works

It's fairly obvious that Oracle WebLogic Server instances have to communicate with one another in order to appear to clients as a single Oracle WebLogic Server instance. Server instances in an Oracle WebLogic Server cluster communicate using the following network technologies:

·         IP multicast or IP unicast for one-to-many communications in the cluster, such as broadcasting heartbeat messages and cluster-wide JNDI updates

·         IP sockets for peer-to-peer communications, such as replicating object states between a primary and secondary server instance

When configuring your cluster, you can select either IP multicast or IP unicast cluster messaging mode for one-to-many communication. The default cluster messaging mode can vary depending on the tool you use to create a cluster. Thus, when creating a cluster with the Configuration Wizard, the default mode is set to unicast. With WSLT, however, multicast is the default. For details on the pros and cons of each messaging mode, consult Using Clusters for Oracle WebLogic Server. It's interesting to note, however, that Oracle recommends unicast for messaging within a cluster when creating new clusters.

As mentioned earlier, IP multicast or unicast is used to, among other things, maintain the cluster-wide JNDI tree, which plays a key role in application deployment. In particular, the JNDI tree used in a clustered environment holds information about the cluster-wide deployed objects and appears to clients as a single, global tree. However, the cluster-wide JNDI tree is replicated across Oracle WebLogic Server instances within a cluster using the cluster-wide JNDI updates mechanism. Thus, each server instance in a cluster maintains its local copy of the cluster-wide JNDI tree, updating that local JNDI tree as the information about new clustered application components comes in through the multicast (or unicast) channel.