High Availability Enterprise Services via JBoss Clusters16.1.�IntroductionClustering allows us to run an applications on several parallel servers (a.k.a cluster nodes). The load is
distributed across different servers, and even if any of the servers fails, the application is still
accessible via other cluster nodes. Clustering is crucial for scalable enterprise applications, as you can
improve performance by simply adding more nodes to the cluster.The JBoss Application Server (AS) comes with clustering support out of the box. The simplest way to start
a JBoss server cluster is to start several JBoss instances on the same local network, using the run
-c all command for each instance. Those server instances, all started in the
all configuration, detect each other and automatically form a cluster.In the first section of this chapter, I discuss basic concepts behind JBoss's clustering services. It is
important that you understand those concepts before reading the rest of the chapter. Clustering
configurations for specific types of applications are covered after this section.