Node groups

A node group is a collection of managed nodes. Managed nodes are WebSphere Application Server nodes. A node group defines a boundary for server cluster formation.


Node groups

Nodes that you organize into a node group need to be similar in terms of installed software, available resources, and configuration to enable servers on those nodes to host the same applications as part of a server cluster. The deployment manager does no validation to guarantee that nodes in a given node group have anything in common.

Node groups are optional and are established at the discretion of the WAS administrator. However, a node must be a member of a node group. Initially, all Application Server nodes are members of the default DefaultNodeGroup node group.

A node can be a member of more than one node group.

Nodes on distributed platforms and the IBM i platform cannot be members of a node group containing a node on a z/OS platform. However, nodes on distributed platforms and nodes on the IBM i platform can be members of the same node group.

To delete a node group, the node group must be empty. The default node group cannot be deleted.

(zos) An Application Server node must be a member of a sysplex node group. Nodes in the same sysplex must be in the same sysplex node group. A node can be in one sysplex node group only.

(zos) When the deployment manager is configured on a z/OS node, the default node group, DefaultNodeGroup, is the sysplex node group for the deployment manager node and any other node in the cell from the same sysplex. Sysplex node groups are special node groups that the system manages.


Sysplex node groups

A sysplex node group is a node group unique to the z/OS operating system. The sysplex node group includes a sysplex name and a z/OS operating system location service configuration. A sysplex is a collection of z/OS systems that cooperate by using certain hardware and software products to process workloads.

We cannot explicitly create a sysplex node group. The z/OS operating system creates sysplex node groups in the following ways:

We cannot remove a node from a sysplex node group. However, if a node is the only member of a sysplex node group, we can add that node to an empty node group. The empty node group is converted into a sysplex node group and the former sysplex node group of the node is converted into a regular node group.

We cannot delete a node group that is a sysplex node group.


Example: Use node groups

By organizing nodes that satisfy the application requirements into a node group, you establish an administrative policy that governs which nodes can be used together to form a cluster. The people who define the cell configuration and the people who create server clusters can operate with greater independence from one another, if they are different people.

In this example, assume the following information:

Applications that exploit WebSphere Business Integration Server Foundation functions can run successfully only on nodes six, seven, and eight. Therefore, clusters that host these applications can be formed only on nodes six, seven, and eight. To define a clustering policy that guides users of the WebSphere cell into building clusters that can span only predetermined nodes, create an additional node group called WBINodeGroup, for example. Add to the node group nodes six, seven, and eight. If we create a cluster on a node from the WBINodeGroup node group, the system allows only nodes from the WBINodeGroup node group to be members of the cluster.

In this next example, assume the following information:

Applications that exploit z/OS functions in the PLEX1 sysplex can run successfully on nodes five and six only. Therefore, clusters that host these applications can be formed only on nodes five and six. The required separation of distributed platform nodes and IBM i platform nodes from z/OS system nodes establishes a natural clustering policy that guides users of the Application Server cell into building clusters that can span only predetermined nodes. If we create a cluster on a node from the PLEX1NodeGroup node group, the system allows only nodes from the PLEX1NodeGroup node group to be members of the cluster.


Related tasks

  • Viewing, configuring, creating, and deleting node groups
  • Create clusters

  • Example: Use node groups with clusters