Configuring the quorum mechanism

The quorum mechanism is configured for each catalog service. You must enable the quorum mechanism on all of the catalog servers in the catalog service domain.

Before you begin

Before you enable the quorum mechanism, you must configure a topology that supports this type of configuration. The configuration must support the following requirements:

About this task

The quorum mechanism is disabled by default. Enable the quorum mechanism in the following scenarios: You can leave the quorum mechanism disabled if your catalog service domain is contained within a single data center, or is on a local area network (LAN). In this type of configuration, default heart beating is used and brownouts are assumed to be shorter than 10 seconds. Because the detection period is approximately 30 seconds, any short brownouts that occur do not cause placement changes to occur in the data grid.

If you enable quorum, all the catalog servers must be available and communicating with the data grid to conduct placement operations. If a network brownout occurs, placement is paused until all the catalog servers are available. If a data center failure occurs, manual administrator actions are required to remove the failed catalog server from the quorum.

Procedure

  1. Enable quorum on the catalog servers.
    In WebSphere Application Server, you must configure quorum with the server properties file. In a stand-alone environment you can either use the properties method or enable quorum when you start the server:
    • Set the enableQuorum=true property in the server properties file.
      You can use this configuration in a WebSphere Application Server or stand-alone environment. See the following example objectGridServer.properties file:
      catalogClusterEndPoints=cat0:cat0.domain.com:6600:6601,
      cat1:cat1.domain.com:6600:6601
      catalogServiceEndPoints= cat0.domain.com:2809, cat1.domain.com:2809
      enableQuorum=true
      For more information about configuring the properties file, see Server properties file.
    • Pass the -quorum enabled flag on the startOgServer command.

      You can use this configuration method when you start stand-alone servers only.

      # bin/startOgServer cat0 –serverProps objectGridServer.properties -quorum true
      For more information about the startOgServer command, see Starting and stopping stand-alone servers.
  2. Start container servers in the same zone.

    When you are running a data grid across data centers, the servers must use the zone information to identify the data center in which they reside. Setting the zone on the container servers allows WebSphere eXtreme Scale to monitor health of the container servers that are scoped to the data center, minimizing cross-data-center traffic. The container server JVMs in a core group must never span multiple LANs that are connected with links, like in a wide area network. See Defining zones for container servers for more information about defining zones for container servers.

    Container server JVMs are tagged with a zone identifier. The data grid of container JVMs is automatically broken in to small core groups of JVMs. A core group only includes JVMs from the same zone. JVMs from different zones are never in the same core group.

    A core group aggressively tries to detect the failure of its member JVMs.

Results

By setting the quorum mechanism to be enabled on the catalog servers within a catalog service domain, all the catalog servers must be available for data grid placement operations to occur. In the event of a short network brownout, placement operations are temporarily stopped until all the catalog servers in the quorum are available.

You can add additional catalog servers to the quorum by repeating these steps.

What to do next