An Overview of Clustering
A WebLogic domain can be extended to incorporate a cluster of servers, typically spread across different physical machines in a network. Usually, a cluster will host a well-defined set of services and J2EE components that form part of a larger application framework. Multiple clusters of server instances, called tiers, are often used to set up the application architecture. These tiers provide both a logical and a physical partitioning of application components that offers greater security, scalability, and fault tolerance. Once you set up the servers that belong to the cluster, you can use the Administration Console to manage its configuration and to monitor its runtime health.
Domains, Machines, and Clusters
As described in Chapter 13, a WebLogic domain can be composed of a number of WebLogic instances, and several of these servers may be grouped into clusters. For instance, you could set up a cluster of WebLogic servers, all of which host your web application and related resources. This cluster of servers could be fronted by a load balancer that distributes requests evenly across all the members of the cluster. The load balancer could itself be another WebLogic instance. All server instances must belong to the same WebLogic domain. Thus, a WebLogic cluster is a group of servers working together with services, such as clustered JNDI, to provide support for failover and load balancing. A domain may in turn have a number of WebLogic instances, several groups ...