Virtus unita fortior. Virtue united is stronger.—; a Latin saying
JBoss clustering is not the product of a single library or specification, but rather a blend of technologies. On the basis of this concept, we decided to split the discussion about clustering into two sessions. In this chapter, we will introduce the rationale behind clustered programming. Here is a preview of what you will learn from this unit:
- What clustering is and how JBoss AS implements it
- The configuration of JBoss AS clustered services
- How to set up additional components required for clustering web applications
A cluster of application servers consists of multiple server instances (cluster nodes) running simultaneously and working together to provide increased scalability and reliability. The nodes that make up the cluster can be either located on the same machine or on different machines. From the client's point of view, this is irrelevant because the cluster appears as a single server instance.
Introducing clustering in your applications will produce the following benefits:
- Scalability: Adding a new node to a cluster should allow the overall system to service a higher client load than that provided by the simple basic configuration. Ideally, it should be possible to service any given load, simply by adding the appropriate number of servers or machines.
- Load balancing: In a clustered environment, the individual nodes composing the cluster should each process a fair share of the overall client load. This can be achieved by distributing client requests across multiple servers, also known as load balancing.
- High availability: Applications running in a cluster can continue when a server instance fails. This is achieved because applications are deployed on multiple nodes of the cluster, and so if a server instance fails, another server instance on which that component is deployed can continue application processing.