WebSphere Application Server V8.5 Administration and Configuration Guide for the Full Profile

650 WebSphere Application Server V8.5 Administration and Configuration Guide for the Full Profile

For more information about creating a cluster, go to the following website:

http://pic.dhe.ibm.com/infocenter/wasinfo/v8r5/index.jsp?topic=%2Fcom.ibm.webspher

e.zseries.doc%2Fae%2Ftrun_wlm_cluster_v61.html

18.2 High availability

The high availability framework that is provided with the product eliminates single points of

failure and provides peer-to-peer failover for applications and processes that are running

within the product environment.

In this section, we provide an overview of the high-availability features in WebSphere

Application Server for z/OS.

18.2.1 High availability manager

High availability manager provides services for product components so that they can make

themselves highly available. By default, the high availability manager instance runs on every

application server, proxy server, node agent, and deployment manager in a cell.

A cell can be divided into multiple high-availability domains known as

core groups. Each high

availability manager instance establishes network connectivity with all other high availability

manager instances in the same core group, using a specialized, dedicated, and configurable

transport channel. The transport channel provides mechanisms that allow the high availability

manager instance to detect when other members of the core group start, stop, or fail.

Automatic restart manager (ARM), Tivoli System Automation, or other automation software

can be configured to restart failed WebSphere Application Server controllers.

Within a core group, high availability manager instances are elected to coordinate high

availability activities. An instance that is elected is known as a

core group coordinator. The

coordinator is highly available, such that if a process that is serving as a coordinator stops or

fails, another instance is elected to assume the coordinator role, without loss of continuity.

The high availability manager periodically runs a number of background tasks, such as

checking the health of highly-available singleton services that it is managing. Most of these

background tasks consume trivial amounts of CPU.

The exceptions are the regularly scheduled Discovery and Failure Detection Protocols:

 The Discovery Protocol discovers when other core group processes start and open

network connections to these other members.

 The View Synchrony Protocol establishes reliable messaging with other core group

members after the connections are opened.

 The Failure Detection Protocol detects when other core group members stop or become

unreachable because of a network partition.

Distribution and Consistency Services

The Distribution and Consistency Services (DCS) transport chain provides the underlying

group services framework for the high availability manager, such that each application server

process knows the health and status of JVMs and singleton services. DCS provides a view of

synchronous services to the high availability manager. DCS itself uses reliable multicast

messaging (RMM) as its publish and subscribe message framework.