WebSphere Application Server V7.0: Concepts ... - IBM Redbooks

This time-out can be configured in the Integrated Solutions Console by
navigating to Servers → Core Groups → →
Discovery and failure detection → Heartbeat timeout period. You can use
this method with multicast emulation. However, this method must be used for
true multicast addressing.
A new feature in WebSphere Application Server V7.0 is the ability to configure an
alternative protocol provider to monitor and manage communication between
core group members. In general, alternate protocol providers, such as the z/OS
Cross-system Coupling Facility (XCF)-based provider, uses less system
resources than the default Discovery Protocol and Failure Detection Protocol,
especially during times when the core group members are idle.
In either case, if a JVM fails, the application server on which it is running is
separated from the core group, and any services running on that application
server are failed over to the surviving core group members.
A JVM can be a node agent, an application server, or a deployment manager. If a
JVM fails, any singletons running in that JVM are activated on a peer JVM after
the failure is detected. This peer JVM is already running and eliminates the
normal startup time, which potentially can be minutes.
This actually is a key difference to using operating system-based high availability.
The high availability manager usually recovers in seconds while operating
system-based solutions take minutes.
When an application server fails, the high availability manager assigns the failing
application servers work to another eligible application server. Using shared
storage for common logging facilities (like the transaction logs) allows the high
availability manager to recover in-doubt and in-flight work if a component fails.
Note: The following Web page provides a testing routine you can use to
determine if your shared file system is suitable for use with the high availability
manager:
http://www-01.ibm.com/support/docview.wss?rs=180&context=SSEQTP&q1=t
ransaction+log+failover&uid=swg24010222&loc=en_US&cs=utf-8&lang=en
Core group
A core group is a high availability domain that consists of a set of processes in
the same cell that can directly establish high availability relationships. Highly
available components can only fail over to another process in the same core
group and replication can occur only between members of the same core group.
252 WebSphere Application Server V7.0: Concepts, Planning, and Design