18.2. Configuring clone resource constraints

You can determine the behavior of a clone resource in a cluster by configuring constraints for that resourse. These constraints are written no differently than those for regular resources except that you must specify the clone’s ID. For information about resource constraints, see Configuring cluster resources.

Clone resource location constraints

In most cases, a clone will have a single copy on each active cluster node. You can, however, set clone-max for the resource clone to a value that is less than the total number of nodes in the cluster. If this is the case, you can indicate which nodes the cluster should preferentially assign copies to with resource location constraints. For general information about location constraints, see Determining which node a resource can run on.

The following command creates a location constraint for the cluster to preferentially assign resource clone webfarm-clone to node1.

# pcs constraint location webfarm-clone prefers node1

Clone resource ordering constraints

Ordering constraints behave slightly differently for clones. In the example below, because the interleave clone option is left to default as false, no instance of webfarm-stats will start until all instances of webfarm-clone that need to be started have done so. Only if no copies of webfarm-clone can be started then webfarm-stats will be prevented from being active. Additionally, webfarm-clone will wait for webfarm-stats to be stopped before stopping itself.

# pcs constraint order start webfarm-clone then webfarm-stats

For general information about resource ordering constraints, see Determining the order in which cluster resources are run.

Clone resource colocation constraints

Colocation of a regular (or group) resource with a clone means that the resource can run on any machine with an active copy of the clone. The cluster will choose a copy based on where the clone is running and the resource’s own location preferences. For information about colocation constraints, see xref colocating-cluster-resources[Colocating cluster resources].

Colocation between clones is also possible. In such cases, the set of allowed locations for the clone is limited to nodes on which the clone is (or will be) active. Allocation is then performed as normally.

The following command creates a colocation constraint to ensure that the resource webfarm-stats runs on the same node as an active copy of webfarm-clone.

# pcs constraint colocation add webfarm-stats with webfarm-clone