Using go-redis with GCP memorystore replicas

[davejohnston]

Hi,
GCP memory store has a Redis implementation. You can either create a Redis cluster, or you can have a single Redis instance with replicas.
Im able to use the go-redis client to connect to and use the single instance redis, but it doesn't look like there is an option to enable the read only replicas (I do see the ReadOnly option, but the docs/comments suggest it only works for cluster clients)

	// Only cluster clients.

	ReadOnly       bool

Has anyone found a way around this, or looked at implementing something that supports it?

Notionally I was thinking we could maintain a map of clients, and keep track of which ones were were only. Ideally a better solution might be something like gorms DBResolver, that picks a primary or replica DB based on the type of command being executed.

Looking at the code that creates the redis client it looks like this

type Client struct {
	*baseClient
	cmdable
	hooks
	ctx context.Context
}

I'm wondering if we could add a field replicaBaseClients []*baseClient

When were executing the command determine if its readonly or write command?

[JavaJourneyer]

hi @davejohnston have you figured out how to use the read replica for reading . in my case , I have a read client and a write client . I am trying to read a key-value using the read client , which errors out. I am able to read/write without any issues using the write client. not sure what the issue is .

[ndyakov]

I am not sure how the GCP memorystore is configured, but in Redis, when you have a standalone client you cannot read from the replica, the replica is there to improve availability. As noted by @JavaJourneyer , it will depend on what type of replicas you have configured:

• https://cloud.google.com/memorystore/docs/redis/high-availability-for-memorystore-for-redis
  If you have the read replicas, you can configure a cluster client with your slots list

  go-redis/osscluster.go

  Line 61 in 03c2c0b

  ClusterSlots func(context.Context) ([]ClusterSlot, error)

  and have the replicas used for reading.