Optional Redis master

[AlexWayfer]

Hello.

We have a Kubernetes setup with Redis sentinels, but without specific master.

From the Redis documentation:

The advantage of having multiple Sentinel processes cooperating are the following:

1. Failure detection is performed when multiple Sentinels agree about the fact a given master is no longer available. This lowers the probability of false positives.

So, master can be unavailable by design. And we're not sure what sentinel is current master.

But, as I see and judging by recieved logs and anycable-helm template, ANYCABLE_REDIS_URL for Redis master is kind of required.

2021-07-16 17:15:07 | I 2021-07-16T14:15:07.586Z context=main Starting AnyCable 1.0.2-ce5b4c5 (pid: 1, open file limit: 1048576)
-- | --
  |   | 2021-07-16 17:15:07 | I 2021-07-16T14:15:07.586Z context=main Handle WebSocket connections at http://0.0.0.0:8080/cable
  |   | 2021-07-16 17:15:07 | I 2021-07-16T14:15:07.586Z context=main Handle health connections at http://0.0.0.0:8080/health
  |   | 2021-07-16 17:15:07 | I 2021-07-16T14:15:07.587Z context=metrics Serve metrics at http://0.0.0.0:8081/metrics
  |   | 2021-07-16 17:15:07 | I 2021-07-16T14:15:07.587Z context=rpc RPC controller initialized: localhost:50051 (concurrency: 28, proto_versions: v0,v1)
  |   | 2021-07-16 17:15:07 | W 2021-07-16T14:15:07.687Z context=pubsub Failed to get master address from sentinel.
  |   | 2021-07-16 17:15:07 | W 2021-07-16T14:15:07.687Z context=pubsub Failed to discover sentinels
  |   | 2021-07-16 17:15:07 | E 2021-07-16T14:15:07.687Z context=main !!! Subscriber failed !!!
  |   | 2021-07-16 17:15:07 | redigo: no sentinels available; last error: redigo: nil returned

Can be Redis master optional and can you tell us how to configure properly for such case?

[Envek]

Hey! Look at description of anycable/anycable-helm#9:

Example of deploying anycable-go with sentinels:

helm install anycable-redis bitnami/redis --set "cluster.enabled=true,sentinel.enabled=true,password=password"
helm install anycable-go anycable/anycable-go --set "env.anycableRedisUrl=redis://:password@mymaster:6379/0,env.anycableRedisSentinels=:password@anycable-redis-headless:26379"

Note that in this example in ANYCABLE_REDIS_URL name of the master instance is specified and in ANYCABLE_REDIS_SENTINELS address of headless service is specified (which points into all redis pods: both initial master and slaves)

When sentinels are used, ANYCABLE_REDIS_URL must contain name of Redis deployment in sentinel configuration as Sentinels can keep track of multiple Redis deployments with different names.

[romcheck]

Hey!
We have the same problem.
What do you mean by 'name of Redis deployment in sentinel configuration'?
We do not have any redis deployment. We use managed redis in some cloud provider and have only sentinel hosts (list of names or ip addresses)

[Envek]

In Redis Sentinel docs it is called master-group-name or name of set of Redis instances. Your cloud provider should also provide this name along with sentinel hosts (by default it can be called mymaster as in examples in the official Redis docs).

[romcheck]

Thanks a lot. It is working now.