Create clusters


 

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Overview

A cluster is a set of appservers managed together as a way to balance workload.

Before creating a cluster...

  1. Decide whether to route enterprise bean requests locally to the node on which the client resides.

  2. Decide to whether use HTTP memory-to-memory replication.

  3. Determine the appropriate settings for the first cluster member.

    A copy of the first cluster member created is stored as part of the cluster data and becomes the template for all additional cluster members that you create.

  4. Decide on which node you want the first cluster member to reside.

Create clusters to:

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


Create a cluster

  1. In the admin console, click...

    Servers | Clusters | WebSphere application server clusters | New

  2. Specify a name for the cluster.

  3. To enable host-scoped routing optimization...

    Prefer local

    This option is enabled by default. When enabled, if possible, EJB requests are routed to the client host. This option improves performance because client requests are sent to local enterprise beans.

  4. To create a memory-to-memory replication domain...

    Set HTTP session memory-to-memory replication

    The replication domain is given the same name as the cluster and is configured with default settings. 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.

    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 | Container settings | Web container settings | Web container | Session management | Distributed environment

    If we change these settings for one cluster member, we might also need to change them for the other members of this cluster.

  5. Click Next.

  6. Create an empty cluster or create the first member of the cluster.

    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 we decide not to create this cluster. To add members to the empty cluster...

      Servers | Clusters | WebSphere application server clusters | cluster_name | Clusters members | New

    By creating 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. 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 that are 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 appserver. The value can range from 0 to 20.

    4. To generate unique port numbers for every HTTP transport that is defined in the source server, select...

      Generate unique HTTP ports

      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.

    5. Select the core group to which you want this cluster member to belong.

      We are prompted for the core group only if we have more than one core group defined for this cluster.

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

      • Create the member using an appserver template.

      • Create the member using an existing appserver as a template.

      • Create the member by converting an existing appserver.

      We can only add an existing application server to the cluster if we select that server as the first cluster member. We cannot add other existing appservers 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, we 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 appserver out of the cluster, we can reuse that server as the template to rebuild the configuration.

  7. Click Next.

  8. Create additional cluster members.

    Before you create additional cluster members, check the settings of the first cluster member. These settings are displayed at the bottom of 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 you want 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 that are 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. Select Generate unique HTTP ports to generate unique port numbers for every HTTP transport that is defined in the source server.

    5. 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.

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

  10. 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.

  11. To further configure a cluster, click...

    Servers | Clusters | WebSphere application server clusters | cluster_name

    Only the Configuration and Local Topology tabs appear until you save the changes.

  12. Click Review to review the cluster settings. Repeat the previous step to make additional configuration changes.

  13. 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.

    If we click Save, but do not select Synchronize changes with Nodes, when you restart the cluster, WAS 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.

  14. Restart the cluster.

 

Next steps


Create a cluster: Basic cluster settings
Create a cluster: Create first cluster member
Create a cluster: Summary settings
Create a cluster: Create additional cluster members
Server cluster collection
Enable static routing for a cluster
Disable static routing for a cluster

 

Related concepts

Introduction: Clusters

 

Related tasks

Create clusters using scripting
Balancing workloads

 

Related

Cluster member templates collection
Cluster configuration scripts
ClusterConfigCommands
migrateServerMEtoCluster