Add members to a cluster

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, we might be managing servers that are at a previous release level, and servers running at the current release level in the same cell.

When we create a cluster, we specify 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 v7.0 node, and a v6.1 node, we can use a server from either the v6.1 or the v7.0 node to create a new cluster member.

When we 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, we must manually configure the virtual host for the new cluster member..

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

Tasks

1. In the administrative 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 that is 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. Using this wizard to add new members to an already configured cluster.

   A copy of the first cluster member that we create is stored as part of the cluster data and becomes the template for all additional cluster members that we 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 v6.1 node and a v7.0 node, the cluster has two templates. The v6.1 template is used when we create an additional cluster member on the v6.1 node, and the v7.0 template is used when creating an additional cluster member on the v7.0 node.

   To view the cluster member templates available for creating a new member of a cluster, in the administrative console, click...

           Servers > Clusters > WebSphere application server clusters > cluster_name > Cluster members > Templates.

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

   2. Select the node for the cluster member.

   3. 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 we specify controls the number of requests that are directed to the application server. Even though we specify a value of 0 to 20 as the weight of a server, the weight givenn 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 that is assigned to the server is the numerator, and the sum of the weights of all members of the cluster is the denominator.

      When we 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 we 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.

      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.

   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 we 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> Edit. When we finish changing the property settings, click Update member to save the changes.

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

3. Click Review, select Synchronize changes with nodes> Save to save the changes.

Created application servers that are members of an existing server cluster.

What to do next

If, when we created the new members, we chose to generate unique ports, update the alias list for the virtual host that we plan to use with the new servers.

We can also perform the following actions:

• On the Cluster members page in the administrative console, click the name of one of the cluster members, and examine the configuration settings for that cluster member. We can change any of the settings that are not appropriate.

  For example, if we do not need to have all of the cluster member components start during the cluster member startup process, we might want to select Start components as needed, which is not automatically selected when a new cluster member is created. When this property is selected, cluster member components are dynamically started as needed. When this property is not selected, all of the cluster member components are started during the startup process. Therefore, selecting this property usually results in improved startup performance because fewer components are started during the startup process.

• Click Servers > Server Types > WebSphere application servers > server or click Servers > Clusters > WebSphere application server clusters > cluster_name > Cluster members > cluster_member_name to perform either of the following tasks:

  • Specify additional application server properties for this cluster member.

  • Click Installed applications.

• (iSeries) Create a backup cluster.

• Start the cluster.

• Use scripting to automate the task of adding cluster members.

Subtopics

• Cluster member collection
  View and manage application servers that belong to a cluster. We can also use this page to change the weight of any of the listed application servers.
• Cluster member settings
  Manage the members of a cluster. A cluster of application servers are managed together and participate in workload management.
• Cluster member templates collection
  View the list of cluster member templates that exist for this cluster. To edit the server properties of a template, click the name of that template.

Related:

Introduction: Clusters

Clusters and workload management

Balancing workloads

Starting clusters

Create backup clusters

Create cluster members using scripting

Modifying cluster member templates

Configure high availability and workload sharing of service integration

Cluster member settings