During an internal MySQL schema upgrade — http://devcentral.nasqueron.org/T646 — the root password has been edited.
Some Docker containers rely on the Docker environment variables propagation through links to connect to the server with the root password. This is the case for Phabricator containers like DevCentral.
Others containers use their own account, and are still operational (like this one).
Update 23:08: All systems are operational.