Add support for Redis cluster via eredis_cluster

[goldyfruit]

Describe your issue or feature request

The current eredis implementation doesn't support Redis cluster which prevent VerneMQ to retrieve the ACL if eredis is not connected to the correct Redis shard.

According to the eredis documentation, they recommend to use eredis_cluster as client when a connection to a Redis cluster is required.

Describe the solution you'd like

The solution could be to add an option like redis.cluster=on, if on then we should load eredis_cluster and configure the client with the correct arguments, if off we should load the standard eredis client.

Describe alternatives you've considered

No response

Environment

• VerneMQ Version: master
• OS: Kubernetes
• Erlang/OTP version (if building from source): 25.2.3
• Cluster size/standalone: 3 pods

Add any other context, code samples or screenshots about the issue report here.

No response

Code of Conduct

• I agree to follow the VerneMQ's Code of Conduct

[ioolkos]

@goldyfruit Thanks for the suggestion. Yeah, we should have a look at both libs.
One question that comes to mind immediately is whether eredis_cluster could be enough (ie whether it could handle the single Redis node too).

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[goldyfruit]

One question that comes to mind immediately is whether eredis_cluster could be enough (ie whether it could handle the single Redis node too).

I would say no, it does not support standalone Redis instance (but I might be wrong), I opened an issue to the project to be sure. 👍

[goldyfruit]

Answer from the opened issue:

Hi!

I believe there is some code for this, yes. If CLUSTER SLOTS fails, there is a fallback to standalone mode. However, there is a lot of overhead compared to using a simple eredis connection.

Btw, in case you're trying out different solutions, we are now actively working on another more efficient cluster client: https://github.com/Ericsson/ered

[ioolkos]

Interesting to see this come out from Ericsson. They clearly label it beta, though.
So, for now, what I would do is a functional test with eredis_cluster and see whether "a lot of overhead" is an issue or not. My guess is not.

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👉 Using the binary VerneMQ packages commercially (.deb/.rpm/Docker) requires a paid subscription.

[goldyfruit]

Interesting to see this come out from Ericsson. They clearly label it beta, though.

Nordic is an initiative from Ericsson I think.

[golfvert]

I'd be also very interested in having the option to use a redis cluster as the auth/auth backend. In my app, along the VerneMQ cluser I already have a redis cluster... Having the option to use a cluster would avoid having a spof.
So, +1 from me :)