The redis gem supports sentinel from version 3.2, redis-sentinel is not necessary if you are using Redis 2.8.x or later.
Another redis automatic master/slave failover solution for ruby by using built-in redis sentinel.
It subscribes message with channel "+switch-master", when message received, it will disconnect current connection and connect to new master server.
Add this line to your application's Gemfile:
gem 'redis-sentinel'
If you are using redis-server less than 2.6.10, please use redis-sentinel 1.3.0
gem 'redis-sentinel', '~> 1.3.0'
And then execute:
$ bundle
Or install it yourself as:
$ gem install redis-sentinel
Specify the sentinel servers and master name
Redis.new(master_name: "master1", sentinels: [{host: "localhost", port: 26379}, {host: "localhost", port: 26380}])
Sentinels can also be specified using a URI. This URI syntax is required when using Rails.config.cache_store:
config.cache_store = :redis_store, { master_name: "master1",
sentinels: ['sentinel://localhost:26379', 'sentinel://localhost:26380'] }
After doing the above, you might still see #<Redis client v3.1.0 for redis://localhost:6379/0>.
This is fine because redis-sentinel will only try to connect when it is actually required.
However, if none of the sentinel servers can be reached, a Redis::CannotConnectError will be thrown.
There are two additional options:
-
:failover_reconnect_timeout(seconds) will block for that long when redis is unreachable to give failover enough time to take place. Does not wait if not given, or time given is 0. -
:failover_reconnect_wait(seconds) how long to sleep after each failed reconnect during a failover event. Defaults to 0.1s.
If you need it, you can get an array of Redis clients, each pointing to one of the slaves:
client = Redis.new(master_name: "master1", sentinels: [{host: "localhost", port: 26379}, {host: "localhost", port: 26380}])
client.slaves
# => [#<Redis client v3.0.7 for redis://127.0.0.1:6380/0>, #<Redis client v3.0.7 for redis://127.0.0.1:6381/0>]
You can also get an array of all the clients (master + slaves):
client = Redis.new(master_name: "master1", sentinels: [{host: "localhost", port: 26379}, {host: "localhost", port: 26380}])
client.all_clients
# => [#<Redis client v3.0.7 for redis://127.0.0.1:6379/0>, #<Redis client v3.0.7 for redis://127.0.0.1:6380/0>, #<Redis client v3.0.7 for redis://127.0.0.1:6381/0>]
Start redis master server, listen on port 16379
$ redis-server example/redis-master.conf
Start redis slave server, listen on port 16380
$ redis-server example/redis-slave.conf
Start 2 sentinel servers
$ redis-server example/redis-sentinel1.conf --sentinel
$ redis-server example/redis-sentinel2.conf --sentinel
$ redis-server example/redis-sentinel3.conf --sentinel
Run example/test.rb, which will query value of key "foo" every second.
$ bundle exec ruby example/test.rb
You will see output "bar" every second. Let's try the failover process.
- Stop redis master server.
- You will see error message output.
- Redis sentinel promote redis slave server to master. During this time you will see errors instead of "bar" while the failover is happening.
- Then you will see correct "bar" output every second again.
Run the same example code above but run:
$ bundle exec ruby example/test_wait_for_failover.rb
You will see the stream of "bar" will stop while failover is taking place and will resume once it has completed, provided that failover takes less than 30 seconds.
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Please fork and contribute, any help in making this project better is appreciated!
This project is a member of the OSS Manifesto.
Copyright @ 2012 - 2015 Richard Huang. See MIT-LICENSE for details