What is a cluster? What is High Availability and Fail over?

Answer Posted / shrinath

A weblogic server cluster consists of multiple weblogic
server server instances running simultaneously working
together to provide increased scalability and reliability.
A cluster appears to clients to be a single weblogic server
instance. the server instances that constitute a cluster can
run on the same machine or be located on different machines.
you can increase a cluster's capacity by adding additional
server instances to the cluster on an existing machine or
you can add machines to the cluster to host the incremental
server instances. Each instance in a cluster must run the
same version of Weblogic Server.
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.

Fail Over:-simple put failover means that when an
application component doing a particular job some set of
processing tasks-becomes unavailable for any reason, a copy
of the failed object finishes the job. Web logic server uses
standards based communication techniques and facilities
including IP sockets and the java Naming and Directory
Interface (JNDI) to share and maintain information about the
availability of objects in a cluster.

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