Add members to a cluster

We can use clusters to balance workload in an environment containing multiple application servers.

Create a cluster if we do not already have a cluster defined for the environment.

If we are migrating from a previous version of the product, we can upgrade a portion of the nodes in a cell, while leaving others at the previous release level. For a time, you might be managing servers that are at a previous release level, and servers that are running at the current release level in the same cell.

When creating a cluster, specified the node on which the first cluster member resides. In a mixed cell environment, we can use any server from within that node group to create a new cluster member. For example, if the node group to which the cluster belongs consists of a Version 7.0 node, and a Version 6.1 node, we can use a server from either the Version 6.1 or the Version 7.0 node to create a new cluster member.

(zos) When you add a member to a cluster, the virtual host for the new cluster member is automatically configured if the deployment manager profile and the managed profile (the cluster member) reside on the same LPAR. Therefore, in this situation, the host alias ports are automatically added to the virtual host for the new cluster member. However, if the deployment manager profile and the managed profile reside on different LPARs, you must manually configure the virtual host for the new cluster member. gotcha

Use the following procedure to create a new cluster member, view information about existing cluster members, or manage existing cluster members.

  1. In the console, click Servers > Clusters > WebSphere application server clusters > cluster_name > Cluster members. The Cluster members page lists members of a cluster, and for each member indicates:

    • The node on which the member resides.

    • The version of the application server. This information specifies whether the cluster is a mixed cluster.

    • The configured weight for the member.

    • The runtime weight for the member. This weight indicates the proportionate workload currently directed to this cluster member.

    • Whether the member is started, stopped, or encountering problems.

  2. Click New to create a new cluster member.

    Clicking New starts the Create a new cluster member wizard. Use this wizard to add new members to an already configured cluster.

    A copy of the first cluster member that you create is stored as part of the cluster data and becomes the template for all additional cluster members that you create. Usually, only one template is available for you to use to create additional cluster members for a cluster. However, if a cluster includes nodes that are at different versions of the product, there is a different template for each version. For example, if a cluster has cluster members that reside on both a Version 6.1 node and a Version 7.0 node, the cluster has two templates. The Version 6.1 template is used when creating an additional cluster member on the Version 6.1 node, and the Version 7.0 template is used when creating an additional cluster member on the Version 7.0 node.

    To view the cluster member templates that are available for creating a new member of a cluster, in the console, click Servers > Clusters > WebSphere application server clusters > cluster_name > Cluster members > Templates.

    1. Specify a name for the application server that you are defining as a cluster member. The name must be unique within the node.

    2. Select the node for the cluster member.

    3. (zos) Specify a short name for this cluster member. The short name is the default job name and identifies the cluster member to the native facilities of the operating system, such as Workload Manager (WLM), Automatic Restart Manager, RACF , and started task control.

    4. Specify the server weight.

      The weight value specified controls the number of requests directed to the application server. Even though specified a value of 0 to 20 as the weight of a server, the weight that is given to the server as a member of a cluster is a proportion based on the weight assigned to the server, and the sum of the weights of all members of the cluster. In this proportion, the weight assigned to the server is the numerator, and the sum of the weights of all members of the cluster is the denominator.

      When you add a new member to a cluster, the number of client, or application requests sent to each server in the cluster decreases, assuming the number of requests coming into the cluster stays the same. Similarly when you remove a new member from a cluster, the number of client or application requests sent to each server in the cluster increases, assuming the number of requests coming into the cluster stays the same.

      For example, if you have a cluster that consists of members A, B, and C with weights 2, 3, and 4, respectively, then 2/9 of the requests are assigned to member A, 3/9 are assigned to member B, and 4/9 are assigned to member C. If a new member, member D, is added to the cluster and member D has a weight of 5, then member A now gets 2/14 of the requests, member B gets 3/14 of the requests, member C gets 4/14 of the requests, and member D gets 5/14 of the requests.

      (zos) On z/OS , weight is used to balance some of the workload types, but others are balanced by the z/OS system.

      • For HTTP requests, weights are used to distribute HTTP traffic between the web server plug-in and the controller handling the clustered application server. Assign a higher weight value to the application server that should receive the HTTP traffic.

      • For web services calls, information is transferred from a servant in one application server to a controller in another application server. The application server that receives the call has the highest weight value.

      • Weight has no affect on Internet Inter-ORB Protocol (IIOP) requests. IIOP requests are distributed to the correct application server using the sysplex distributor.

      Avoid trouble: For workload balancing with service integration, or with message driven beans in the application server, you require additional configuration. See the topic Configure high availability and workload sharing of service integration for more information.gotcha

    5. Specify whether to generate unique HTTP ports.

    6. Click Add member to finish defining the cluster member. The first cluster member for this cluster is used as the template for this cluster member. We can repeat these steps to define other cluster members.

    7. When you finish defining additional cluster members, review the summary information for the new cluster members. If we have to change any of the property settings for any of the new members, select that cluster member, and then click Edit. When you finish changing the property settings, click Update member to save the changes.

    8. When you finish defining new cluster members, click Next to view the summary page for the cluster, and then click Finish to create these new cluster members.

  3. Click Review, select Synchronize changes with nodes, and then click Save to save the changes.


Results

We created application servers that are members of an existing server cluster.


What to do next

If, when creating the new members, you chose to generate unique ports, update the alias list for the virtual host to use with the new servers.

We can also perform the following actions:


Subtopics


Related concepts

  • Introduction: Clusters
  • Clusters and workload management


    Related tasks

  • Balancing workloads
  • Start clusters

    Create backup clusters

  • Create cluster members
  • Modify cluster member templates
  • tjt0023_.html

    Cluster member settings