When a 3scale uses external DBs like PostgreSQL, Oracle, MySQL, and Redis, it isn't clear the 3scale side procedures while updating an external DB.
The steps should be like so: 

1. Plan the external DB upgrade procedure (customer's responsibility)
2. Inform users of the upcoming maintenance window and what impact that will have on service availability (assuming the services that depend on that DB will be unavailable then the customer should make that clear and is also their responsibility)
3. Take the necessary actions on the 3scale side i.e. if it's a single DB instance that will be upgraded and unavailable then scale down the pods which claim the PV mounting that DB (standard DB admin exercise)
4. Perform upgrade according to DB documentation
5. Complete DB upgrade and revert the actions taken on the 3scale side in the previous steps

Item 3 should be documented in detail.
For example, although the 3scale 2.12 document mentions that users must upgrade to PostgreSQL 13, it doesn't explain the procedure.
Please clarify 3scale side procedures when using an external DB and updating the external DB.