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

For certain functions (like transaction peer recovery) the high availability
manager takes advantage of fault tolerant storage technologies such as Network
Attached Storage (NAS), which significantly lowers the cost and complexity of
high availability configurations. The high availability manager also provides
peer-to-peer failover for critical services by maintaining a backup for these
services. WebSphere Application Server also supports other high availability
solutions such as HACMP, Parallel Sysplex, and so on.
A high availability manager continually monitors the application server
environment. If an application server component fails, the high availability
manager takes over the in-flight and in-doubt work for the failed server. This
introduces some overhead but significantly improves application server
availability.
A high availability manager focuses on recovery support and scalability in the
following areas:
► Embedded messaging
► Transaction managers
► Workload management controllers
► Application servers
► WebSphere partitioning facility instances
► On-demand routing
► Memory-to-memory replication through Data Replication Service (DRS)
► Resource adapter management
To provide this focused failover service, the high availability manager supervises
the JVMs of the application servers that are core group members. The high
availability manager uses one of the following methods to detect failures:
► An application server is marked as failed if the socket fails.
This method uses the KEEP_ALIVE function of TCP/IP and is tolerant of poor
performing application servers, which might happen if the application server is
overloaded, swapping, or thrashing. This method is recommended for
determining a JVM failure if you are using multicast emulation and are
running enough JVMs on a single application server to push the application
server into extreme processor starvation or memory starvation.
► A JVM is marked as failed if it stops sending heartbeats for a specified time
interval.
This method is referred to as active failure detection. When it is used, a JVM
sends out one heartbeat, or pulse, at a specific interval. This interval can be
configured in the Integrated Solutions Console by navigating to Servers →
Core Groups → → Discovery and failure detection
→ Heartbeat transmission period. If the JVM does not respond to
heartbeats within a defined time frame, it is considered down.
Chapter 7. Performance, scalability, and high availability 251