A service that is represented by one resource group might depend so strongly on a service in a second resource group that both services must run on the same node. For example, an application that is comprised of multiple interdependent service daemons might require that all daemons run on the same node.
In this situation, force the resource group of the dependent service to be collocated with the resource group of the other service. To enforce collocation of a resource group with another resource group, declare on the resource group a strong positive affinity for the other resource group.
# clresourcegroup set|create -p RG_affinities=++target-rg source-rg
Specifies the resource group that is the source of the strong positive affinity. This resource group is the resource group on which you are declaring a strong positive affinity for another resource group.
Specifies the resource group that is the target of the strong positive affinity. This resource group is the resource group for which you are declaring a strong positive affinity.
A resource group follows the resource group for which it has a strong positive affinity. If the target resource group is relocated to a different node, the source resource group automatically switches to the same node as the target. However, a resource group that declares a strong positive affinity is prevented from failing over to a node on which the target of the affinity is not already running.
Only failovers that are initiated by a resource monitor are prevented. If a node on which the source resource group and target resource group are running fails, both resource groups fail over to the same surviving node.
For example, a resource group rg1 declares a strong positive affinity for resource group rg2. If rg2 fails over to another node, rg1 also fails over to that node. This failover occurs even if all the resources in rg1 are operational. However, if a resource in rg1 attempts to fail over rg1 to a node where rg2 is not running, this attempt is blocked.
The source of a strong positive affinity might be offline on all nodes when you bring online the target of the strong positive affinity. In this situation, the source of the strong positive affinity is automatically brought online on the same node as the target.
For example, a resource group rg1 declares a strong positive affinity for resource group rg2. Both resource groups are initially offline on all nodes. If an administrator brings online rg2 on a node, rg1 is automatically brought online on the same node.
You can use the clresourcegroup suspend command to prevent a resource group from being brought online automatically due to strong affinities or cluster reconfiguration.
If you require a resource group that declares a strong positive affinity to be allowed to fail over, you must delegate the failover. For more information, see Delegating the Failover or Switchover of a Resource Group.
This example shows the command for modifying resource group rg1 to declare a strong positive affinity for resource group rg2. As a result of this affinity relationship, rg1 is brought online only on nodes where rg2 is running. This example assumes that both resource groups exist.
# clresourcegroup set -p RG_affinities=++rg2 rg1