6.3. Colocation of Resources

A colocation constraint determines that the location of one resource depends on the location of another resource.

There is an important side effect of creating a colocation constraint between two resources: it affects the order in which resources are assigned to a node. This is because you cannot place resource A relative to resource B unless you know where resource B is. So when you are creating colocation constraints, it is important to consider whether you should colocate resource A with resource B or resource B with resource A.

Another thing to keep in mind when creating colocation constraints is that, assuming resource A is collocated with resource B, the cluster will also take into account resource A's preferences when deciding which node to choose for resource B.

The following command creates a colocation constraint.

pcs constraint colocation add [master|slave] source_resource with [master|slave] target_resource [score] [options]

pcs constraint colocation add [master|slave] source_resource with [master|slave] target_resource [score] [options]

For information on master and slave resources, see Section 8.2, “Multi-State Resources: Resources That Have Multiple Modes”.

Table 6.3, “Properties of a Colocation Constraint”. summarizes the properties and options for configuring colocation constraints.

pcs constraint colocation add myresource1 with myresource2 score=INFINITY

# pcs constraint colocation add myresource1 with myresource2 score=INFINITY

pcs constraint colocation add myresource1 with myresource2 score=-INFINITY

# pcs constraint colocation add myresource1 with myresource2 score=-INFINITY