Just to clarify, the
mysql-shared interface is intended to be used when the charm needs a database that can be shared across multiple applications, or if the application needs the database to have a specific name instead of getting a randomly generated database name. In that context, the
configure call is actually correct, in that it is required to inform the database of the desired name and other admin info.
As far as I could tell, the usage was correct, so it seems like there was a bug in the database charm being connected to, or in the interface layer. You might try with one of the other charms that provide that relation interface, such as MariaDB, Percona Cluster, or Galera Cluster.
But, if you don’t need the named database functionality, then the plain
mysql interface is fine to use instead.