This task is about phasing out the co-located Redis instances on MW's memcached servers, which was historically used for MW's session storage and MW's main stash, both of which have or are being migrated to other backends.
With T212129 done, the redis_sessions cluster is not in use anymore, so, it is high time we removed it!
Background
We have been discussing this topic for a few quarters now, it is time we do the final pushes to get to it. Please attach any relevant tasks and update the description with a checklist accordingly.
We are planning to keep this cluster to version Redis 2.8, even after we upgrade those hosts to buster, but this is putting an administrative overhead of keeping and maintaining a very old Redis version T265643