With a static cluster, you would manually start or stop the cluster, or the JVMs in the cluster. With a dynamic cluster, there are 3 modes, and each mode determines how the cluster or cluster members can stopped or started.
- Manual mode – you have to manually start or stop the cluster members
- Supervised mode - Tasks are created to advise the administrator to start and stop the cluster members
- Automatic mode - cluster members stop and start automatically
To select a mode:
- In the left panel of the WebSphere admin console, select Servers > Clusters > Dynamic clusters.
- There is a drop down to select supervised, automatic, or manual. Checkmark a cluster, select a mode, and select Set Mode.
The change will take effect immediately. In other words, the change will be written to the master repository as soon as you select Set Mode.
When manual mode is selected, you can manually start or stop the cluster members.
When supervised mode is selected, you can manually start or stop the cluster members. With supervised mode, tasks will be created to advise you to either start or stop a cluster member. The task can be viewed at System administration > Task management > Runtime tasks.
The application placement controller creates the tasks. Typically, the application placement controller will be propertly configured to create the tasks. In other words, you usually do not need to tune the application placement controller.
When automatic mode is selected, the application placement controller will start or stop cluster members. To view the configuration for the application placement controller, select Operational policies > Autonomic managers > Application placement controller. Typically, the application placement controller will be propertly configured to start and stop dynamic cluster members.
By default, the dynamic cluster wil be configured so that at least one cluster member will remain running, which prevents the application placement controller from stopping all of the cluster members.