Implement cluster API

[mijicd]

Extracted from this comment authored by @regis-leray.

Commands

• CLUSTER ASK When a cluster client receives an -ASK redirect, command is sent to the target node followed by the command which was redirected.
• CLUSTER ADDSLOTS slot [slot ...] Assign new hash slots to receiving node
• CLUSTER BUMPEPOCH Advance the cluster config epoch
• CLUSTER COUNT-FAILURE-REPORTS node-id Return the number of failure reports active for a given node
• CLUSTER COUNTKEYSINSLOT slot Return the number of local keys in the specified hash slot
• CLUSTER DELSLOTS slot [slot ...] Set hash slots as unbound in receiving node
• CLUSTER FAILOVER [FORCE|TAKEOVER] Forces a replica to perform a manual failover of its master.
• CLUSTER FLUSHSLOTS Delete a node's own slots information
• CLUSTER FORGET node-id Remove a node from the nodes table
• CLUSTER GETKEYSINSLOT slot count Return local key names in the specified hash slot
• CLUSTER INFO Provides info about Redis Cluster node state
• CLUSTER KEYSLOT key Returns the hash slot of the specified ke- [ ]
• CLUSTER MEET ip port Force a node cluster to handshake with another node
• CLUSTER MYID Return the node id
• CLUSTER NODES Get Cluster config for the node
• CLUSTER REPLICATE node-id Reconfigure a node as a replica of the specified master node
• CLUSTER RESET [HARD|SOFT] Reset a Redis Cluster node
• CLUSTER SAVECONFIG Forces the node to save cluster state on disk
• CLUSTER SET-CONFIG-EPOCH config-epoch Set the configuration epoch in a new node
• CLUSTER SETSLOT slot IMPORTING|MIGRATING|STABLE|NODE [node-id] Bind a hash slot to a specific node
• CLUSTER SLAVES node-id List replica nodes of the specified master node
• CLUSTER REPLICAS node-id List replica nodes of the specified master node
• CLUSTER SLOTS Get array of Cluster slot to node mappings- [ ]
• READONLY Enables read queries for a connection to a cluster replica node
• READWRITE Disables read queries for a connection to a cluster replica node

Tips

• Define the API in zio.redis.api.
• Command-specific options should be defined in zio.redis.options.
• Additional inputs and outputs can be defined in zio.redis.Input and zio.redis.Output, respectively.
• Redis API evolves, therefore the commands listed above might be slightly changed. Double check the official docs before starting with implementation.
• Use telnet to understand command protocol details.
• Write inputs and outputs tests in zio.redis.InputSpec and zio.redis.OutputSpec, respectively.
• Write integration tests by expanding the zio.redis.ApiSpec.
• If you feel that the pull request size is growing out of control, feel free to split it but make sure to link this issue in each of the related PRs.

[rby]

I'll take a look at this.

[mijicd]

@rby Nice, thanks for taking care of this. Note that this might be a significant chunk of work, so feel free to split it in whatever way you find convenient. You might have to adjust, or separate communication channels here.

[rby]

I did some exploration, but got stuck on an issue with the protocol when clustering is enabled:
basically this is a telnet session with a cluster:

Escape character is '^]'.
set a 1
-MOVED 15495 :0

vs, with a standalone:

Escape character is '^]'.
set a 1
+OK

so all tests are broken already :-)

[mijicd]

@rby that is somewhat expected as clustering works a bit differently. I'm afraid we'll need to have a separate executor to support that.

[rby]

progress so far

• the docker-compose-cluster.yml should help with tests/integration

I guess the next step is to split a task for a RedisClusterExecutor or similar?

[mijicd]

I'd propose to have a minimal working version in this PR, i.e. connecting to cluster fully works. Once that's in place, the other commands can go in separate PRs.

[mijicd]

@rby I think it might be worth to check https://github.com/antirez/redis-rb-cluster for some ideas how to implement the new executor or modify the existing one.

[rby]

@mijicd yup that's what I've been doing the last couple of hours.
My guess is:

• implement cluster nodes command and make it available in the RedisExecutor
• a Layer to build some kind of ClusterRedisExecutor from a non empty list of RedisExecutor (startup nodes)
• the layer needs to call cluster nodes on the first available node
• build the pool of nodes if needed
• then from there try to understand the slot hashing and figure out how to redirect calls.
• figure out the next bridge to build
  wdyt?
  It's a heavy issue indeed :-)

[mijicd]

@rby Sounds good to me.

Perhaps there's a chance to reuse the existing executor, but just build it differently, by passing the CRC stuff while building layer, but this is just me speaking out loud.

Regarding the difficulty, I didn't mark it as a good first issue for reason(s) :). However, if we'd manage to have a poc of a single command, that would be amazing.

[rby]

@mijicd I made some progress, I'll try to test what I have so far without docker-compose as nodes weren't reachable when topology fetched through cluster info command.

[rby]

All right, I have a test that passes with sAdd, sCard :-)

[mijicd]

@rby wow, nice. Sorry for the late response, I'll take a look at it. Btw. you could open up a draft PR so that everyone can chime in there.

[anatolysergeev]

@rby hello. I wonder, would you continue work on that issue? 2 months have passed since you started, mb you need some help or if you don't want to do that issue anymore, I can replace you?
Sorry, no offences. I need this functionality for my projects at work.))
With appreciation)

[rby]

@anatolysergeev on the contrary it would be great if you take over.
best luck 👍

[anatolysergeev]

I'm think that implementation of the other cluster commands isn't priority now due to their low use by users in business logic. That's why i want focus on other issues, that thinks are more important. Feel free to take this issue, i move away from it for now.

[drmarjanovic]

@anatolysergeev I would start working on this issue. Do you have any in-progress commands, or I can freely choose commands?