Interest in supporting AWS Elasticache replication group failover

[craigmcnamara]

I made a gem here: https://github.com/craigmcnamara/redis-elasticache

I'd happily make it an optional addon to redis-rb if you'd accept a pull request.

[ndbroadbent]

Hi @craigmcnamara, thanks for working on this! I didn't realize I would need to do something extra to support ElastiCache failover. I have seen some ReadOnly errors in the past that this gem should fix, so I will try it out!

However, now I'm struggling with a different error during failover: #949

Would the redis-elasticache addon also help with this?

Also, does redis-elasticache break a standard Redis installation? (e.g. during tests on CI, or for other deployments that don't use ElastiCache.) Do you think it is safe to always use redis-elasticache, or should I add a way to manually enable it when needed?

Thanks!

[ndbroadbent]

Ahh, I can see the code just checks for some error messages and raises a different error to force a reconnect: https://github.com/craigmcnamara/redis-elasticache/blob/master/lib/redis/elasticache/failover.rb

So it looks like this won't help with my current issue, but I'll definitely use this anyway! Thanks!

[uiur]

I was seeing a similar issue,
but I've found that current elasicache doesn't have this issue by default.

close-on-replica-write is enabled by default, and it disconnects connections with write command to replica automatically.

If enabled, clients who attempt to write to a read-only replica will be disconnected.

https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/ParameterGroups.Redis.html#ParameterGroups.Redis.2-8-23

[timanovsky]

I was seeing a similar issue,
but I've found that current elasicache doesn't have this issue by default.

close-on-replica-write is enabled by default, and it disconnects connections with write command to replica automatically.

If enabled, clients who attempt to write to a read-only replica will be disconnected.

https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/ParameterGroups.Redis.html#ParameterGroups.Redis.2-8-23

It may still be needed. Looks like LUA invocations are not handled properly and still fail with READONLY error

[jebw]

For anyone upgrading to Redis 5 gem, looks like this maybe fixed in v5.0.6 now

https://github.com/redis/redis-rb/blob/master/CHANGELOG.md#506

#1168