Upgrade keycloak in containerized environment (production)

Reading the upgrade guide, I wasn’t able to understand how in practice keycloak server (or a cluster of servers) should be updated in containerized environment.

First of all, should the upgrade script be run at all? how? If using newer keycloak image for the new servers, what should be done? Should we expect downtime (since it’s stated that the server should be stopped before running the upgrade script, if it’s relevant at all when using docker images)

Second, should we let the new server version upgrade the DB automatically or should we manually upgrade the DB?

And Fourth, what about backward compatibility with the older server versions? From the upgrade guide it seems that the old servers stop working after the upgrade, I assume it’s due to the DB upgrade. Is there a way to prevent downtime while upgrading ?