There are some MySQL tables without primary keys, namely:

ezurl_object_link, eztipafriend_request, migrations

Missing primary keys have known issues in the Percona XtraDB Cluster and should be avoided.

Making the multiple key in ezurl_object_link a primary one is not possible due to https://jira.ez.no/browse/EZP-23423 (duplicated entries). For the other two tables it should be possible to set the columns as primary key.