Handling Redis Cluster configured with cluster-preferred-endpoint-type hostname

[slai11]

In Redis v7.0, clusterbus extension and hostname support was added which (among other things) adds hostname information into CLUSTER NODES and CLUSTER SLOTS response.

Key changes:

• CLUSTER SLOTS returns the preferred endpoint under its networking information. This means https://github.com/redis/redis-rb/blob/v4.8.0/lib/redis/cluster/slot_loader.rb will construct a hash with preferred endpoints for keys.
• CLUSTER NODES appends the hostname to the node address portion. This means https://github.com/redis/redis-rb/blob/v4.8.0/lib/redis/cluster/node_loader.rb constructs a hash IP addresses for keys regardless of the preferred endpoint.

Effects on redis-rb 4.x

Assuming we connect to a Redis Cluster on v7.0 with cluster-preferred-endpoint-type set to hostname.

The Redis::Cluster object will have node_flags made up of ip -> role whereas available_slots made up of hostname -> slots.

The @map in Slot object will be configured with the wrong master nodes since every key lookup in @node_flags will return nil.

With wrongly configured master nodes for a substantial % of the slots, subsequent Redis commands will receive MOVED redirections. This affects performance and possible raise false positives for error metrics on the client side.

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At GitLab, we are using redis-rb v4.8.0 and encountered a steady rate of MOVED redirections as a result. We have monkey-patched it via https://gitlab.com/gitlab-org/gitlab/-/merge_requests/112691 in the meantime.

I understand that the project is not testing against Redis v7.0 in the CI (looking at the actions), but would you be open to a PR to upstream our patch? We would be more than happy to prepare a PR.

[byroot]

I understand that the project is not testing against Redis v7.0 in the CI (looking at the actions)

I'm not sure what gave you this impression:

redis-rb/.github/workflows/test.yaml

Line 224 in e4f5299

REDIS_BRANCH: "7.0"

but would you be open to a PR to upstream our patch?

For the current main branch yes, but I'm not interested in a backport for 4.x.

[slai11]

Ah apologies. I missed out Cluster when checking https://github.com/redis/redis-rb/actions/runs/4142117293.

For the current main branch yes, but I'm not interested in a backport for 4.x.

That sounds fair 👍 . For the main branch, I've opened a PR in redis-rb/redis-cluster-client@f173f91. It's merged and looks like it will be released in 0.4.3.

In that case, I shall close the issue. Thank you!