5.5. Resource Groups

One of the most common elements of a cluster is a set of resources that need to be located together, start sequentially, and stop in the reverse order. To simplify this configuration, Pacemaker supports the concept of groups.

You create a resource group with the following command, specifying the resources to include in the group. If the group does not exist, this command creates the group. If the group exists, this command adds additional resources to the group. The resources will start in the order you specify them with this command, and will stop in the reverse order of their starting order.

pcs resource group add group_name resource_id...

You can also add a new resource to an existing group when you create the resource, using the following command. The resource you create is added to the group named group_name.

pcs resource create resource_id standard:provider:type|type [resource_options] [op operation_action operation_options] --group group_name

You remove a resource from a group with the following command. If there are no resources in the group, this command removes the group itself.

pcs resource group remove group_name resource_id...

The following command lists all currently configured resource groups.

pcs resource group list

The following example creates a resource group named shortcut that contains the existing resources IPaddr and Email.

# pcs resource group add shortcut IPaddr Email

There is no limit to the number of resources a group can contain. The fundamental properties of a group are as follows.

If a resource in the group cannot run anywhere, then no resource specified after that resource is allowed to run.

Obviously as the group grows bigger, the reduced configuration effort of creating resource groups can become significant.