While greenfield applications are easy to get started on with Cloud SQL, many teams will want to capitalize on the managed MySQL and PostgreSQL experience for existing databases hosted outside of Google Cloud. With first generation MySQL instances, it was possible to configure external masters. This provided a clear migration path as the new instance could simply replicate all data from the external master until eventually moving clients over to the new instance.

With second generation instances, external masters are currently not supported. Migration to a second generation MySQL instance will unfortunately require some level of downtime, as writes must be disabled for the original MySQL instance and data must be imported into the new instance. The total downtime can be drastically reduced by migrating historical data before disabling writes on...