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With the introduction of the Liberty collective, we are also pleased to announce Liberty clusters. New in WebSphere Application Server 8.5.5, Liberty clusters provide centralized administrative support for application clusters. This new support does not invalidate clustering models available in WebSphere Application Server Liberty V8.5, rather it allows for formalizing cluster definitions and enables centralized management of those clusters. Part of a Liberty Collective by design Collective members are not necessarily part of a cluster, but all cluster members must belong to a collective; this is necessary to provide the centralized administrative support for Liberty clusters. A Liberty cluster, also called a cluster group, is the set of cluster members which belong to the same cluster within the same collective. A Liberty profile server can only be a member of one cluster at any given time. Collaborating Liberty Profiles by intent Cluster groups are defined by enabling the clusterMember-1.0 feature in the collective members which should be treated as a single application cluster. By default, cluster members are part of the “defaultCluster” group, but a specific cluster group can be specified by optionally defining a cluster name. For example, to define a collective member as part of the “blogCluster”, add the following configuration to the member’s server.xml: The member will publish its cluster assignment to the controller (which requires the member to have been started). To add more collective members to the same cluster, simply enable the clusterMember-1.0 feature and define the same value for the Homogenous by best practice Clusters should be homogenous, which means they should share a common configuration for security, application resources and of course the applications themselves. There is no enforcement mechanism within the Liberty cluster support to prevent cluster members from having divergent configuration but there are a set of recommended best practices, such as shared configuration, which allows each server within the cluster to separate the common configuration for the applications from the server specific configuration (such as port numbers). Accessible by “group” operations The following cluster operations are provided through the collective controller’s ClusterManager MBean:
The full API documentation can be found in the dev/api/ibm/javadoc/com.ibm.websphere.appserver.api.collectiveController_1.0.0-javadoc.zip file within the Liberty installation. Comprised of independent members Like collective members, cluster membership is “opt-in” and loosely-coupled. Cluster members can still be managed individually, and cluster members can be easily moved into or out of a cluster through a simple configuration action. Liberty cluster support does not include the Intelligent Management capabilities provided in WebSphere Application Server Full Profile, but continues the plugin-cfg.xml support provided in WebSphere Application Server Liberty V8.5. |
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