Server, Cluster and Domain

Server: Well, we all know what a server is so lets talk abt Cluster and Domain :}

Cluster: A Server cluster consists of multiple server instances running simultaneously and working together to provide increased scalability and reliability

A cluster appears to clients to be a single Server instance.

Domain: A domain includes one or more Server instances, which can be clustered, non-clustered, or a combination of clustered and non-clustered instances. A domain can include multiple clusters. A domain also contains the application components deployed in the domain, and the resources and services required by those application components and the server instances in the domain. Examples of the resources and services used by applications and server instances include machine definitions, optional network channels, connectors, and startup classes.


In each domain, one Server instance acts as the Administration Server.—the server instance which configures, manages, and monitors all other server instances and resources in the domain. Each Administration Server manages one domain only. If a domain contains multiple clusters, each cluster in the domain has the same Administration Server.


you cannot "split" a cluster over multiple domains.Similarly, you cannot share a configured resource or subsystem between domains. For example, if you create a JDBC connection pool in one domain, you cannot use it with a server instance or cluster in another domain. (Instead, you must create a similar connection pool in the second domain.)


Benefits of Clustering:

Scalability
The capacity of an application deployed on a WebLogic Server cluster can be increased dynamically to meet demand. You can add server instances to a cluster without interruption of service—the application continues to run without impact to clients and end users.

High-Availability
In a WebLogic Server cluster, application processing can continue when a server instance fails. You "cluster" application components by deploying them on multiple server instances in the cluster—so, if a server instance on which a component is running fails, another server instance on which that component is deployed can continue application processing.

Capabilities of a Cluster

Failover: Using session replication and replica-aware stubs
Load Balancing

Objects that can be clustered

Servlets, JSPs ,EJBs ,Remote Method Invocation (RMI) objects ,Java Messaging Service(JMS) destinations ,Java Database Connectivity (JDBC) connections


Objects that cannot be clustered

File services ,Time services ,WebLogic Events (deprecated in WebLogic Server 6.0) ,Workspaces (deprecated in WebLogic Server 6.0)