Application monitoring prerequisites and considerations

Keep the following in mind:

• Any application to be monitored must be defined to an application controller in an existing cluster resource group.
• If you have configured dependent resource groups, we recommend to configure multiple monitors:
  • For applications included in parent resource groups, and for applications in child resource groups.
  • For applications included in target resource groups, and for applications in source resource groups in start after dependency and stopafter dependency
  For example, a monitor for a parent resource group can monitor the successful startup of the application, and a monitor for a child resource group can monitor the process for an application. For more information, see Monitor modes.
• Multiple monitors can be configured for the same application controller. Each monitor can be assigned a unique name in SMIT.
• The monitors that you configure must conform to existing configuration rules. For more information, see Configuring a process application monitor and Configuring a custom application monitor.
• It is recommend that you first configure an application controller, and then configure the monitor(s) that you can associate with the application controller. Before configuring an application monitor, configure all your application controllers. Then configure the monitors and associate them with the controllers. You can go back at any time and change the association of monitors to controllers.
• You can configure no more than 128 monitors per cluster. No limit exists on the number of monitors per application controller, as long as the total number of all monitors in the cluster is less than 128.
• When multiple monitors are configured that use different fallover policies, each monitor specifies a failure action of either "notify" or "fallover". PowerHA® SystemMirror® processes actions in the order in which the monitors indicate an error. For example, if two monitors are configured for an application controller and one monitor uses the "notify" method and the other uses the "fallover" method, the following occurs:
  • If a monitor with "fallover" action indicates an error first, PowerHA SystemMirror moves the resource group to another node, and the remaining monitor(s) are shut down and restarted on another node. PowerHA SystemMirror takes no actions specified in any other monitor.
  • If a monitor with "notify" action indicates an error first, PowerHA SystemMirror runs the "notify" method and shuts down that monitor, but any remaining monitors continue to operate as before. You can manually restart the "notify" monitor on that node using the Suspend/Resume Application Monitoring SMIT panel.
• If multiple monitors are used, PowerHA SystemMirror does not use a particular order for the monitors startup or shutdown. All monitors for an application controller are started at the same time. If two monitors are configured with different fallover policies, and they fail at precisely the same time, PowerHA SystemMirror does not guarantee it processes methods specified for one monitor before methods for the other.
• The same monitor can be associated with multiple application controllers using the Application Monitor(s) field in the Change/Show an Application Controller SMIT panel. You can select a monitor from the picklist.
• If you remove an application monitor, PowerHA SystemMirror removes it from the definition for all application controllers that were using the monitor, and indicates which application controllers are no longer using the monitor.
• If you remove an application controller, PowerHA SystemMirror removes it from the definition of all application monitors that were configured to monitor the application. PowerHA SystemMirror also sends a message about which monitor will no longer be used for the application. If you remove the last application controller in use for any particular monitor, that is, if the monitor will no longer be used for any application, verification issues a warning that the monitor will no longer be used.
• If you configure an application monitor for an application controller, PowerHA SystemMirror starts the monitor when the application is being brought online to determine the state of the application. PowerHA SystemMirror event processing is suspended for the number of seconds specified in the stabilization interval for the monitoring script . If you did not configure an application monitor, PowerHA SystemMirror event processing is suspended for 10 seconds to allow the application to start.