Investigate for Client-side caching using Redis Cluster and Master/Replica

Feature Request

v6 introduces an awesome new feature (Server-assisted Client-side caching support). There is a limitation currently where it can only be used with Redis Standalone setups. It would be great to extend this support for Redis Cluster and Master/Replica environments.

See https://github.com/lettuce-io/lettuce-core/issues/1281#issuecomment-669028055 for more details.

Is your feature request related to a problem? Please describe

No

Describe the solution you’d like

Client side caching to work with Redis Cluster and Master/Replica.

Describe alternatives you’ve considered

N/A

Teachability, Documentation, Adoption, Migration Strategy

Ideally it would just use the new CacheFrontend in v6 such that the Redis topology doesn’t matter.

[blasphemic]

I’m sorry if you felt if my comment was trying to shame you; it was of course not intended that way. I was merely trying to express that this feature (which is awesome in itself) simply lose some if its value if only usable in certain circumstances.

I don’t expect anything from open-source projects. It is just a bonus when things like this simply work.

[mp911de]

There are a few challenges to address:

1. Re-apply CLIENT TRACKING settings upon reconnect: While that is primary a resiliency feature, in Master/Replica or Cluster mode that is a must since we don’t get hold easily of cluster connections. We also need to apply tracking settings when creating a new connection
2. Topology changes: Whenever the topology changes, we need to adapt to that. Meaning also that we need to carry over tracking settings. More over, how does the migration path look like when in Redis Cluster a slot assignment gets migrated to a new node? What about the server side, does it carry over also all touched keys? I assume not so reconfiguration can cause dropped notifications since the new server is no longer aware of the key subscriptions from the old server. While this could be done (with a lot of effort) on the client side, I think that is too complex.
3. Finally, I don’t have time to do that in the near future nor I see how I can do that alone in 2021.

Please also refer to #1467 which isn’t solved and a pre-requisite to all future work.