Was updating to stable (v2.7.8) in the first container having SKIP_POST_DEPLOYMENT_MIGRATIONS enabled.
When running the second time in the other container with the skip-option disabled the migration task CorrectlyMoveAssignmentsFromCustomFieldsToATable failed:
PG::NotNullViolation: ERROR: null value in column "assigned_to_type" of relation "assignments" violates not-null constraint
As far I can see the upgrade task AddAssignedToTypeToAssignments (creating the not-null constraint) should not be performed until CorrectlyMoveAssignmentsFromCustomFieldsToATable has been finished.
As workaround I was doing:
INSERT INTO assignments (assigned_to_id, assigned_by_user_id, topic_id, created_at, updated_at,assigned_to_type) SELECT assigned_to.value::integer, assigned_by.value::integer, assigned_by.topic_id, assigned_by.created_at, assigned_by.updated_at, 'User' FROM topic_custom_fields assigned_by INNER JOIN topic_custom_fields assigned_to ON assigned_to.topic_id = assigned_by.topic_id WHERE assigned_by.name = 'assigned_by_id' AND assigned_to.name = 'assigned_to_id' ORDER BY assigned_by.created_at DESC ON CONFLICT DO NOTHING; INSERT INTO schema_migration_details (version, name, hostname, git_version, rails_version, duration, direction, created_at) values( '20210714173022', 'CorrectlyMoveAssignmentsFromCustomFieldsToATable', 'ce4fb45daf62', '98b0621d538fa4e8a53e1e74127c24c384be9b58', '18.104.22.168', 0, 'up', '2021-09-28 15:20:00.123456' ); INSERT INTO schema_migrations values('20210714173022');
Afterwords I was able to rebuild the container.