The basic peer-to-peer (both client and server function, or both
mode) topology is the default configuration and has a single replica. However,
you can also add additional replicas by configuring the replication domain.
In this basic peer-to-peer topology, each server Java Virtual Machine (JVM)
can:
- Host the Web application leveraging the HTTP session
- Send out changes to the HTTP session that it owns
- Receive backup copies of the HTTP session from all of the other servers
in the cluster
This configuration represents the most consolidated topology, where the
various system parts are collocated and requires the fewest server processes.
When using this configuration, the most stable implementation is achieved
when each node has equal capabilities (CPU, memory, and so on), and each handles
the same amount of work.
It is also important
to note that when using the peer-to-peer topology, that one session replication
backup must run at all times for invalidation to occur. For example, if you
have a cluster of 2 application servers, server1 and server2, that are both
configured in the peer-to-peer mode and server2 goes down. All of backup information
for server1 is lost and those sessions are no longer invalidated properly.
Session hot failover
New feature: A new feature called session hot failover has been added
to this release. This feature is only applicable to the peer-to-peer mode.
In a clustered environment, session affinity in the WebSphere Application
Server plug-in routes the requests for a given session to the same server.
If the current owner server instance of the session fails, then the WebSphere
Application Server plug-in routes the requests to another appropriate server
in the cluster. For a cluster configured to run in the peer-to-peer mode
this feature causes the plug-in to failover to a server that already contains
the backup copy of the session, therefore avoiding the overhead of session
retrieval from another server containing the backup. However, hot failover
is specifically for servant region failures. When an entire server, meaning
both controller and server fail, sessions may have to be retrieved over the
network.
newfeat
You must upgrade all WebSphere Application Server plug-in
instances that front the Application Server cluster to version 6.0 to ensure
session affinity when using the peer-to-peer mode.