Redis Cluster Client

This library is a client for Redis cluster. It depends on redis-client. So it would be better to read redis-client documents first.

Background

This gem is underlying in the official gem which is named as redis-clustering. The redis-clustering gem was decoupled from the redis gem since v5 or later. Both are maintained by the repository in the official organization. The redis gem supported cluster mode since the pull request was merged until v4. You can see more details and reasons in the issue if you have interest.

Installation

gem 'redis-cluster-client'

Initialization

key	type	default	description
:nodes	String or Hash or Array<String, Hash>	['redis://127.0.0.1:6379']	node addresses for startup connection
:replica	Boolean	false	true if client should use scale read feature
:replica_affinity	Symbol or String	:random	scale reading strategy, :random, random_with_primary or :latency are valid
:fixed_hostname	String	nil	required if client should connect to single endpoint with SSL
:slow_command_timeout	Integer	-1	timeout used for "slow" queries that fetch metdata e.g. CLUSTER NODES, COMMAND
:concurrency	Hash	{ model: :on_demand, size: 5}	concurrency settings, :on_demand, :pooled and :none are valid models, size is a max number of workers, :none model is no concurrency, Please choose the one suited your environment if needed.
:connect_with_original_config	Boolean	false	true if client should retry the connection using the original endpoint that was passed in
:max_startup_sample	Integer	3	maximum number of nodes to fetch CLUSTER NODES information for startup

Also, the other generic options can be passed. But :url, :host, :port and :path are ignored because they conflict with the :nodes option.

require 'redis_cluster_client'

# The following examples are Docker containers on localhost.
# The client first attempts to connect to redis://127.0.0.1:6379 internally.

# To connect to primary nodes only
RedisClient.cluster.new_client
#=> #<RedisClient::Cluster 172.20.0.2:6379, 172.20.0.6:6379, 172.20.0.7:6379>

# To connect to all nodes to use scale reading feature
RedisClient.cluster(replica: true).new_client
#=> #<RedisClient::Cluster 172.20.0.2:6379, 172.20.0.3:6379, 172.20.0.4:6379, 172.20.0.5:6379, 172.20.0.6:6379, 172.20.0.7:6379>

# To connect to all nodes to use scale reading feature + make reads equally likely from replicas and primary
RedisClient.cluster(replica: true, replica_affinity: :random_with_primary).new_client
#=> #<RedisClient::Cluster 172.20.0.2:6379, 172.20.0.3:6379, 172.20.0.4:6379, 172.20.0.5:6379, 172.20.0.6:6379, 172.20.0.7:6379>

# To connect to all nodes to use scale reading feature prioritizing low-latency replicas
RedisClient.cluster(replica: true, replica_affinity: :latency).new_client
#=> #<RedisClient::Cluster 172.20.0.2:6379, 172.20.0.3:6379, 172.20.0.4:6379, 172.20.0.5:6379, 172.20.0.6:6379, 172.20.0.7:6379>

# With generic options for redis-client
RedisClient.cluster(timeout: 3.0).new_client

# To connect with a subset of nodes for startup
RedisClient.cluster(nodes: %w[redis://node1:6379 redis://node2:6379]).new_client

# To connect with a subset of auth-needed nodes for startup

## with URL:
### User name and password should be URI encoded and the same in every node.
username = 'myuser'
password = URI.encode_www_form_component('!&<123-abc>')
RedisClient.cluster(nodes: %W[redis://#{username}:#{password}@node1:6379 redis://#{username}:#{password}@node2:6379]).new_client

## with options:
RedisClient.cluster(nodes: %w[redis://node1:6379 redis://node2:6379], username: 'myuser', password: '!&<123-abc>').new_client

# To connect to single endpoint
RedisClient.cluster(nodes: 'redis://endpoint.example.com:6379').new_client

# To connect to single endpoint with SSL/TLS (such as Amazon ElastiCache for Redis)
RedisClient.cluster(nodes: 'rediss://endpoint.example.com:6379').new_client

# To connect to NAT-ted endpoint with SSL/TLS (such as Microsoft Azure Cache for Redis)
RedisClient.cluster(nodes: 'rediss://endpoint.example.com:6379', fixed_hostname: 'endpoint.example.com').new_client

# To specify a timeout for "slow" commands (CLUSTER NODES, COMMAND)
RedisClient.cluster(slow_command_timeout: 4).new_client

# To specify concurrency settings
RedisClient.cluster(concurrency: { model: :on_demand, size: 6 }).new_client
RedisClient.cluster(concurrency: { model: :pooled, size: 3 }).new_client
RedisClient.cluster(concurrency: { model: :none }).new_client

# The above settings are used by sending commands to multiple nodes like pipelining.
# Please choose the one suited your workloads.

# To reconnect using the original configuration options on error. This can be useful when using a DNS endpoint and the underlying host IPs are all updated
RedisClient.cluster(connect_with_original_config: true).new_client

Interfaces

The following methods are able to be used like redis-client.

• #call
• #call_v
• #call_once
• #call_once_v
• #blocking_call
• #blocking_call_v
• #scan
• #sscan
• #hscan
• #zscan
• #pipelined
• #multi
• #pubsub
• #close

The #scan method iterates all keys around every node seamlessly. The #pipelined method splits and sends commands to each node and aggregates replies. The #multi method supports the transaction feature but you should use a hashtag for your keys. The #pubsub method supports sharded subscriptions. Every interface handles redirections and resharding states internally.

Multiple keys and CROSSSLOT error

A subset of commands can be passed multiple keys. In cluster mode, these commands have a constraint that passed keys should belong to the same slot and not just the same node. Therefore, the following error occurs:

$ redis-cli -c mget key1 key2 key3
(error) CROSSSLOT Keys in request don't hash to the same slot

$ redis-cli -c cluster keyslot key1
(integer) 9189

$ redis-cli -c cluster keyslot key2
(integer) 4998

$ redis-cli -c cluster keyslot key3
(integer) 935

For the constraint, Redis cluster provides a feature to be able to bias keys to the same slot with a hash tag.

$ redis-cli -c mget {key}1 {key}2 {key}3
1) (nil)
2) (nil)
3) (nil)

$ redis-cli -c cluster keyslot {key}1
(integer) 12539

$ redis-cli -c cluster keyslot {key}2
(integer) 12539

$ redis-cli -c cluster keyslot {key}3
(integer) 12539

In addition, this gem works multiple keys without a hash tag in MGET, MSET and DEL commands using pipelining internally automatically. If the first key includes a hash tag, this gem sends the command to the node as is. If the first key doesn't have a hash tag, this gem converts the command into single-key commands and sends them to nodes with pipelining, then gathering replies and returning them.

r = RedisClient.cluster.new_client
#=> #<RedisClient::Cluster 127.0.0.1:6379>

r.call('mget', 'key1', 'key2', 'key3')
#=> [nil, nil, nil]

r.call('mget', '{key}1', '{key}2', '{key}3')
#=> [nil, nil, nil]

This behavior is for upper libraries to be able to keep a compatibility with a standalone client. You can exploit this behavior for migrating from a standalone server to a cluster. Although multiple-time queries with single-key commands are slower than pipelining, that pipelined queries are slower than a single-slot query with multiple keys. Hence, we recommend to use a hash tag in this use case for the better performance.

Transactions

This gem supports Redis transactions, including atomicity with MULTI/EXEC, and conditional execution with WATCH. Redis does not support cross-node transactions, so all keys used within a transaction must live in the same key slot. To use transactions, you can use #multi method same as the redis-client:

cli.multi do |tx|
  tx.call('INCR', 'my_key')
  tx.call('INCR', 'my_key')
end

More commonly, however, you will want to perform transactions across multiple keys. To do this, you need to ensure that all keys used in the transaction hash to the same slot; Redis a mechanism called hashtags to achieve this. If a key contains a hashag (e.g. in the key {foo}bar, the hashtag is foo), then it is guaranted to hash to the same slot (and thus always live on the same node) as other keys which contain the same hashtag.

So, whilst it's not possible in Redis cluster to perform a transction on the keys foo and bar, it is possible to perform a transaction on the keys {tag}foo and {tag}bar. To perform such transactions on this gem, use the hashtag:

cli.multi do |tx|
  tx.call('INCR', '{user123}coins_spent')
  tx.call('DECR', '{user123}coins_available')
end

# Conditional execution with WATCH can be used to e.g. atomically swap two keys
cli.call('MSET', '{myslot}1', 'v1', '{myslot}2', 'v2')
cli.multi(watch: %w[{myslot}1 {myslot}2]) do |tx|
  old_key1 = cli.call('GET', '{myslot}1')
  old_key2 = cli.call('GET', '{myslot}2')
  tx.call('SET', '{myslot}1', old_key2)
  tx.call('SET', '{myslot}2', old_key1)
end
# This transaction will swap the values of {myslot}1 and {myslot}2 only if no concurrent connection modified
# either of the values

You can early return out of your block with a next statement if you want to cancel your transaction. In this context, don't use break and return statements.

# The transaction isn't executed.
cli.multi do |tx|
  next if some_conditions?

  tx.call('SET', '{key}1', '1')
  tx.call('SET', '{key}2', '2')
end

# The watching state is automatically cleared with an execution of an empty transaction.
cli.multi(watch: %w[{key}1 {key}2]) do |tx|
  next if some_conditions?

  tx.call('SET', '{key}1', '1')
  tx.call('SET', '{key}2', '2')
end

RedisClient::Cluster#multi is aware of redirections and node failures like ordinary calls to RedisClient::Cluster, but because you may have written non-idempotent code inside your block, the block is called once if e.g. the slot it is operating on moves to a different node.

IMO

https://redis.io/docs/interact/transactions/#errors-inside-a-transaction

Errors happening after EXEC instead are not handled in a special way: all the other commands will be executed even if some command fails during the transaction. It's important to note that even when a command fails, all the other commands in the queue are processed - Redis will not stop the processing of commands.

$ telnet 127.0.0.1 6379
set key3 a
+OK
multi
+OK
set key3 b
+QUEUED
incr key3
+QUEUED
exec
*2
+OK
-ERR value is not an integer or out of range
get key3
$1
b

The SET command was processed because the INCR command was queued.

multi
+OK
set key3 c
+QUEUED
mybad key3 d
-ERR unknown command 'mybad', with args beginning with: 'key3' 'd'
exec
-EXECABORT Transaction discarded because of previous errors.
get key3
$1
b

The SET command wasn't processed because of the error during the queueing.

https://redis.io/docs/interact/transactions/#what-about-rollbacks

Redis does not support rollbacks of transactions since supporting rollbacks would have a significant impact on the simplicity and performance of Redis.

It's hard to validate them perfectly in advance on the client side. It seems that Redis aims to prior simplicity and performance efficiency. So I think it's wrong to use the transaction feature by complex ways. To say nothing of the cluster mode because of the CAP theorem. Redis is just a key-value store.

ACL

The cluster client internally calls COMMAND and CLUSTER NODES commands to operate correctly. So please permit it like the followings.

# The default user is administrator.
cli1 = RedisClient.cluster.new_client

# To create a user with permissions
# Typically, user settings are configured in the config file for the server beforehand.
cli1.call('ACL', 'SETUSER', 'foo', 'ON', '+COMMAND', '+CLUSTER|NODES', '+PING', '>mysecret')

# To initialize client with the user
cli2 = RedisClient.cluster(username: 'foo', password: 'mysecret').new_client

# The user can only call the PING command.
cli2.call('PING')
#=> "PONG"

cli2.call('GET', 'key1')
#=> NOPERM this user has no permissions to run the 'get' command (RedisClient::PermissionError)

Otherwise:

RedisClient.cluster(username: 'foo', password: 'mysecret').new_client
#=> Redis client could not fetch cluster information: NOPERM this user has no permissions to run the 'cluster|nodes' command (RedisClient::Cluster::InitialSetupError)

Connection pooling

You can use the internal connection pooling feature implemented by redis-client if needed.

# example of docker on localhost
RedisClient.cluster.new_pool(timeout: 1.0, size: 2)
#=> #<RedisClient::Cluster 172.21.0.3:6379, 172.21.0.6:6379, 172.21.0.7:6379>

Connection drivers

Please see redis-client.

Development

Please make sure the following tools are installed on your machine.

Tool	Version	URL
Docker	latest stable	https://docs.docker.com/engine/install/
Docker Compose	V2	https://docs.docker.com/compose/reference/
Ruby	latest stable	https://www.ruby-lang.org/en/
Bundler	latest satble	https://bundler.io/

Please fork this repository and check out the codes.

$ git clone git@github.com:your-account-name/redis-cluster-client.git
$ cd redis-cluster-client/
$ git remote add upstream https://github.com/redis-rb/redis-cluster-client.git
$ git fetch -p upstream

Please install libraries.

$ bundle install --path=.bundle --jobs=4

Please run Redis cluster with Docker.

## If you use Docker server and your OS is Linux:
$ docker compose up

## else:
$ HOST_ADDR=192.168.xxx.xxx docker compose -f compose.nat.yaml up
$ DEBUG=1 bundle exec rake 'build_cluster[192.168.xxx.xxx]'

### When the above rake task is not working:
$ docker compose -f compose.nat.yaml exec node1 bash -c "yes yes | redis-cli --cluster create --cluster-replicas 1 $(seq 6379 6384 | xargs -I {} echo 192.168.xxx.xxx:{} | xargs echo)"

Please run basic test cases.

$ bundle exec rake test

You can see more information in the YAML file for GItHub actions.

Migration

This library might help you if you want to migrate your Redis from a standalone server to a cluster. Here is an example code.

# frozen_string_literal: true

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'redis-cluster-client'
end

src = RedisClient.config(url: ENV.fetch('REDIS_URL')).new_client
dest = RedisClient.cluster(nodes: ENV.fetch('REDIS_CLUSTER_URL')).new_client
node = dest.instance_variable_get(:@router).instance_variable_get(:@node)

src.scan do |key|
  slot = ::RedisClient::Cluster::KeySlotConverter.convert(key)
  node_key = node.find_node_key_of_primary(slot)
  host, port = ::RedisClient::Cluster::NodeKey.split(node_key)
  src.blocking_call(10, 'MIGRATE', host, port, key, 0, 7, 'COPY', 'REPLACE')
end

It needs more enhancement to be enough performance in the production environment that has tons of keys. Also, it should handle errors.

See also

• https://redis.io/docs/reference/cluster-spec/
• redis/redis-rb#1070
• redis/redis#8948
• valkey-io/valkey#384
• https://github.com/antirez/redis-rb-cluster
• https://twitter.com/antirez
• http://antirez.com/latest/0
• https://www.youtube.com/@antirez
• https://www.twitch.tv/thetrueantirez/