Create clusters

A cluster is a set of application servers that you manage together as a way to balance workload.

Before creating a cluster:

You might want to create a cluster if we need to:

A cluster enables you to manage a group of application servers as a single unit, and distribute client requests among the application servers that are members of the cluster.

(zos) If we plan to create a cluster of servers that spans multiple systems in a sysplex and has stateful session beans with an activation policy of Transaction deployed in them, the passivation directory should reside on an HFS (hierarchical file system) that is shared across the multiple systems in the sysplex on which the clustered servers are running.

To create a cluster:

  1. In the console, click Servers > Clusters > WebSphere application server clusters > New. The Create a new cluster wizard starts.

  2. Specify a name for the cluster.

  3. (zos) Optional: Specify a short name for the cluster.

    For clustered servers, the WLM application environment is the default value for the cluster short name. If we specify a short name for a cluster, the name:

    • Must be one to eight characters in length.

    • Must contain only alpha-numeric or national language characters.

    • Cannot start with a number.

    • Must be unique in the cell.

    • Cannot be the same as the value specified on the ClusterTransitionName custom property of any non-clustered server. Do not specify a cluster transition name for a server that is part of a cluster.

    Avoid trouble: If we specify a short name, make sure set up a RACF SERVER class profile that includes this short name.gotcha

  4. Select Prefer local to enable host-scoped routing optimization. This option is enabled by default. When this option is enabled, if possible, EJB requests are routed to the client host. This option improves performance because client requests are sent to local enterprise beans.

    Supported configurations: If we enable the preferLocal optimization, the deployment manager must be running to affect the configuration. If the deployment manager is shut down, preferLocal optimization is not performed and requests might be dispersed across all the members of the cluster.

  5. Select Configure HTTP session memory-to-memory replication if you want a memory-to-memory replication domain created for this cluster. The replication domain is given the same name as the cluster and is configured with the default settings for a replication domain. When the default settings are in effect, a single replica is created for each piece of data and encryption is disabled. Also, the web container for each cluster member is configured for memory-to-memory replication.

    If the WAS cluster has session Memory to Memory replication enabled, then the plug-in configuration file for that server cluster must have the GetDWLMTable property set to true.

    To change these settings for the replication domain, click Environment > Replication domains > replication_domain_name. To modify the web container settings, click Servers > Clusters > WebSphere application server clusters > cluster_name > Clusters members > cluster_member_name. Then, in the Container settings section, click Web container settings > Web container >Session management > Distributed environment settings in the console. If we change these settings for one cluster member, you might also need to change them for the other members of this cluster.

  6. Click Next.

  7. Choose whether to create an empty cluster or to create the first member of the cluster.

    If we decide to create an empty cluster, to add members to this cluster, in the console, click Servers > Clusters > WebSphere application server clusters > cluster_name > Clusters members > New.

    To create an empty cluster:

    1. Select None. Create an empty cluster.

    2. Click Next to display a summary of the defined cluster.

    3. Click Finish to create the cluster, or click Cancel if you decide not to create this cluster.

    When you create the first cluster member, remember that 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.

    1. Specify the name of the first cluster member.

    2. Select the node on which you want this cluster member to reside.

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

    4. Specify the weight value for the cluster member. The weight value controls the amount of work that is directed to the application server. If the weight value for this server is greater than the weight values assigned to other servers in the cluster, then this server receives a larger share of the workload. The weight value represents a relative proportion of the workload assigned to a particular application server. The value can range from 0 to 20.

      (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.

    5. Select Generate unique HTTP ports to generate unique port numbers for every HTTP transport defined in the source server. When this option is selected, which is the default setting, this cluster member does not have HTTP transports or HTTP transport channels that conflict with any of the other servers defined on the same node. If we unselect this option, all of the cluster members will share the same HTTP ports.

    6. Select the core group to which you want this cluster member to belong. You are prompted for the core group only if you have more than one core group defined for this cluster.

    7. Select one of the following options to determine how the server resources are promoted in the cluster.

      • Cluster to move the resources of the first cluster member to the cluster level. The resources of the first cluster member replace the resources of the cluster.

      • Server to maintain the server resources at the new cluster member level. The cluster resources remain unchanged.

      • Both to copy the resources of the cluster member (server) to the cluster level. The resources of the first cluster member replace the resources of the cluster. The same resources exist at both the cluster and cluster member scopes.

    8. Select one of the following options as the basis for the first cluster member.

      • Create the member using an application server template.

        (zos) If we select the defaultZOS template, which is the only one that is listed unless you used the createServerTemplate command (AdminTask) to create additional templates, the first cluster member uses the default port assignments for z/OS. If some of these ports are already defined for use elsewhere in the system, the newly created cluster member might not start, might function incorrectly, or might generate unexpected error messages. Therefore, you must resolve any port conflicts before you start this server.

      • Create the member using an existing application server as a template.

      • Create the member by converting an existing application server.

      Avoid trouble: We can only add an existing application server to the cluster if you select that server as the first cluster member. We cannot add other existing application servers to that cluster after you create the first cluster member. If we add an existing server to a cluster, the only way to remove that server from the cluster is to delete the server. Therefore, you might want to use the existing server as a template for the first cluster member instead of as the cluster member. If we keep the original application server out of the cluster, we can reuse that server as the template if we need to rebuild the configuration.gotcha

  8. Click Next.

  9. Create additional cluster members. Before creating additional cluster members, check the configuration settings of the first cluster member. These settings are displayed on the Create additional cluster members panel of the Create a new cluster wizard. For each additional member to create:

    1. Specify a unique name for the member. The name must be unique within the node.

    2. Select the node to which to assign the cluster member.

    3. Specify the weight you want given to this member. The weight value controls the amount of work that is directed to the application server. If the weight value for the server is greater than the weight values assigned to other servers in the cluster, then the server receives a larger share of the workload. The value can range from 0 to 20.

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

    5. Select Generate unique HTTP ports to generate unique port numbers for every HTTP transport defined in the source server.

    6. Click Add member. We can edit the configuration settings of any of the newly created cluster members other than the first cluster member, or we can create additional cluster members. Click Previous to edit the properties of the first cluster member. The settings for the first cluster member become the settings for the cluster member template that is automatically created when creating the first cluster member.

  10. When you finish creating cluster members, click Next.

  11. View the summary of the cluster and then click Finish to create the cluster, click Previous to return to the previous wizard panel and change the cluster, or click Cancel to exit the wizard without creating the cluster.

  12. To further configure a cluster, click Servers > Clusters > WebSphere application server clusters > , and then click the name of the cluster. Only the Configuration and Local Topology tabs appear until you save the changes.

  13. Click Review to review the cluster configuration settings. Repeat the previous step if we need to make additional configuration changes.

  14. If we do not want to make any additional configuration changes, select Synchronize changes with Nodes and then click Save. Your changes are saved and synchronized across all of the nodes.

    Avoid trouble: If we click Save, but do not select Synchronize changes with Nodes, when you restart the cluster, the product does not start the cluster servers because it cannot find them on the node. To always synchronize the configuration changes across the nodes, we can select Synchronize changes with Nodes as one of the console preferences.gotcha

  15. Restart the cluster.


Results

You have created a cluster to which we can assign work requests. The Runtime and Local Topology tabs appear the next time you access this page.


What to do next


Subtopics


Related concepts

  • Introduction: Clusters


    Related tasks

  • Create clusters

  • Cluster member templates collection

    (zos) Controlling application environments with RACF server class profiles

    (zos) Resource Access Control Facility Tips for customizing WebSphere Application Server

    (zos) SAF profile prefixes and the customization jobs

  • Cluster configuration scripts
  • ClusterConfigCommands (AdminTask)
  • migrateServerMEtoCluster command