Finagle Redis does not handle operation redirects

[bm1549]

The existing Finagle Redis client does not handle operation redirects such as MOVED and ASK. It appears that this may have been supported as part of #648 but that PR was never merged.

Expected behavior

When a server in the Redis cluster responds with MOVED, the Redis client should follow the redirect to the other server.

Actual behavior

The redis client returns an error, for example com.twitter.finagle.redis.ServerError: MOVED 8607 172.16.0.4:6379

Steps to reproduce the behavior

1. Use Redis in cluster-mode
2. Fetch a key that exists on a node other than the primary
3. Notice exception is thrown and the correct value is not returned

[mosesn]

@bm1549 would you be interested in taking a stab at this? The cluster client hasn't historically been partition-aware, so I think a simple approach to this would be augmenting ServerError to treat MOVED specially so that clients know how to handle it, and a more sophisticated approach would be to try to make the redis cluster client partition-aware.

[bm1549]

@mosesn #648 seems to have implemented that, but it was never merged. I could re-open that PR and make any necessary adjustments to handle a merge conflict, but I don't have the time required to implement anything further. Let me know if that would be helpful and I can spend some time on that in the coming weeks.

[linzhiqi]

As the solution hasn't got released, I want to try lettuce to interact with redis cluster. The problem I'm facing is how would I make sure the client is gracefully shutdown before it's garbage-collected. @mosesn