Create clusters

Client requests are distributed among the cluster members on a single machine. A client refers to any servlet, Java application, or other program or component that connects the end user and the application server being used accessed.

1. Decide which application server we want to cluster.

2. Decide whether we want to replicate data.

   Replication is a service that transfers data, objects, or events among application servers.

   Create a replication domain when creating a cluster.

3. Deploy the application onto the application server.

4. Create a cluster.

   After configuring the application server and the application components exactly as we want them to be, create a cluster. The original server instance becomes a cluster member that is administered through the cluster.

5. Create one or more cluster members.

6. (iSeries) Configure a backup cluster.

   If we have clients running in an environment:

   • That includes Java thin clients,
   • Where requests are being routed between multiple cells, or
   • Where requests are being routed within a single cell that includes nodes from earlier versions of the product,

   They might suddenly encounter a situation where the port information about the cluster members of the target cluster has become stale.

   This situation most commonly occurs when all of the cluster members have dynamic ports and are restarted during a time period when no requests are being sent. The client process in this state will eventually attempt to route to the node agent to receive the new port data for the cluster members, and then use that new port data to route back to the members of the cluster.

   If any issues occur that prevent the client from communicating with the node agent, or that prevent the new port data being propagated between the cluster members and the node agent, request failures might occur on the client. In some cases, these failures are temporary. In other cases we need to restart one or more processes to resolve a failure.

   To circumvent the client routing problems that might arise in these cases, we can configure static ports on the cluster members. With static ports, the port data does not change as a client process gets information about the cluster members. Even if the cluster members are restarted, or there are communication or data propagation issues between processes, the port data the client holds is still valid. This circumvention does not necessarily solve the underlying communication or data propagation issues, but removes the symptoms of unexpected or uneven client routing decisions.

   A backup cluster handles requests if the primary cluster fails.

7. Start the cluster.

   When we start the cluster, all of the application servers that are members of that cluster start. Workload management automatically begins after the cluster members start.

8. After the cluster is running, we can perform the following tasks:

   • Stop the cluster.

   • Upgrade the applications installed on the cluster members.

   • Detect and handle problems with server clusters and their workloads.

   • Change how frequently the workload management state of the client refreshes.

     The default timeout value for JVM property com.ibm.CORBA.RequestTimeout is 0, which means wait forever. This default value is not a good setting to have for failover situations. Therefore, if the application is experiencing problems with timeouts, or if we have configured the system for failover situations, use the -CCD option on the LaunchClient command to set an appropriate non-zero value for this property.

     If the workload management state of the client refreshes too soon or too late, change the interval setting of the JVM custom property...

     com.ibm.websphere.wlm.unusable.interval

What to do next

For stand-alone Java clients, define a bootstrap host. Stand-alone Java clients are clients located on a different machine from the application server and have no administrative server. Add the following line to the Java virtual machine (JVM) arguments for the client:

-Dcom.ibm.CORBA.BootstrapHost=machine_name

...where machine_name is the name of the machine on which the administrative server is running.

Subtopics

• Clusters and workload management
  
• Workload management (WLM) for z/OS
  
• Set up a highly available sysplex environment
  
• Enable multiple servants on z/OS
  
• Classifying z/OS workload
  
• Create clusters
  
• Create backup clusters
  
• Starting clusters
  
• Add members to a cluster
  
• Replicating data across application servers in a cluster
  
• Delete clusters
  
• Tune a workload management configuration
  
• Troubleshoot workload management
  

Related:

Introduction: Clusters

Cluster member settings

Cluster member collection

Server cluster settings

Server cluster collection