Comment 6 for bug 1532085

In practice, a lot of charms seem to generally make the assumption that there is in fact a leader at all times (particularly clustered charms, e.g. hacluster, percona, ceph-mon).

Such charms often gate various hook changes on is_leader where the affects are cluster-wide so as not to act on them multiple times. For example making changes to the pacemaker CIB resources in the hacluster charm. Pacemaker itself synchronizes this across the cluster so it only needs to be done on one node.

In many cases they won't "re-do" those changes if re-elected leader (although some charms also do in practice "re-do" such things by iterating all relations under some hooks.. mostly as a workaround to having no other way to detect if something the relations care about, e.g. configuration changes, will affect them.