Using shadow resources

You can use shadow resources to set up relationships between fixed resources running on different nodes.

A shadow resource has the following characteristics:

It is a fixed resource of class IBM.Application that monitors the OpState of another fixed resource.
It is member of an equivalency whose SelectFromPolicy attribute value is set to NoControl, which specifies that System Automation for Multiplatforms evaluates only the OpState of the member resources but does not start or stop them.

You must use shadow resources if you want to define a relationship of type DependsOn from a floating resource to one out of two or more fixed resources that are running on different nodes because the DependsOn relationship triggers both a StartAfter and a StopAfter behavior.

If you set up such a DependsOn relationship without defining shadow resources, an undesired automation behavior occurs:

Figure 1. Scenario 1: DependsOn relationship, without shadow resources

In Scenario 1, System Automation for Multiplatforms stops the floating resource if one of the fixed resources is not available, and System Automation for Multiplatforms can only restart the floating resource if both of the fixed resources are available.

To achieve the wanted automation behavior, you create shadow resources that are members of a NoControl equivalency:

Figure 2. DependsOn relationship, with shadow resources

In Scenario 2, the ForceDown behavior of the DependsOn relationship causes System Automation for Multiplatforms to stop the floating resource if the operational state of the currently selected member of the equivalency changes to Offline, but now System Automation for Multiplatforms can restart the floating resource again if at least one other member of the equivalency is online.