[Ruby on Rails (RoR)] Use Redis Cache Store in Rails

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Redis Cache Store

The Redis cache store takes advantage of Redis support for automatic eviction when it reaches max memory, allowing it to behave much like a Memcached cache server.

Deployment note: Redis doesn’t expire keys by default, so take care to use a dedicated Redis cache server. Don’t fill up your persistent-Redis server with volatile cache data! Read the Redis cache server setup guide in detail.

For a cache-only Redis server, set maxmemory-policy to one of the variants of allkeys. Redis 4+ supports least-frequently-used eviction (allkeys-lfu), an excellent default choice. Redis 3 and earlier should use least-recently-used eviction (allkeys-lru).

Set cache read and write timeouts relatively low. Regenerating a cached value is often faster than waiting more than a second to retrieve it. Both read and write timeouts default to 1 second, but may be set lower if your network is consistently low-latency.

By default, the cache store will not attempt to reconnect to Redis if the connection fails during a request. If you experience frequent disconnects you may wish to enable reconnect attempts.

Cache reads and writes never raise exceptions; they just return nil instead, behaving as if there was nothing in the cache. To gauge whether your cache is hitting exceptions, you may provide an error_handler to report to an exception gathering service. It must accept three keyword arguments: method, the cache store method that was originally called; returning, the value that was returned to the user, typically nil; and exception, the exception that was rescued.

Use :redis_cache_store >= Rails 5.2

Rails 5.2.0 includes a Redis cache store out of the boxBuilt-in Redis cache store by jeremy · Pull Request #31134 · rails/rails · GitHub - https://github.com/rails/rails/pull/31134, so you don’t really need this gem anymore if you just need to store the fragment cache in Redis. Maintenance on the redis-activesupport gem will continue for security and compatibility issues, but we are no longer accepting new features. We are still actively maintaining all other gems in the redis-store family, such as [redis-actionpack for session management, and redis-rack-cache for HTTP cache storage.

To get started, add the redis gem to your Gemfile:

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# Gemfile

# GitHub - redis/redis-rb: A Ruby client library for Redis
# https://github.com/redis/redis-rb
gem 'redis', '4.3.1'

You can enable support for the faster hiredis connection library by additionally adding its ruby wrapper to your Gemfile:

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# Gemfile

# redis/hiredis-rb: Ruby wrapper for hiredis
# https://github.com/redis/hiredis-rb
gem 'hiredis', '0.6.3'

Redis cache store will automatically require & use hiredis if available. No further configuration is needed.

Finally, add the configuration in the config/environment.rb or relevant config/environments/*.rb file:

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config.cache_store = :redis_cache_store, { url: ENV['REDIS_URL'] }

A more complex, production Redis cache store may look something like this:

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# config/environment.rb or config/environments/*.rb

cache_servers = %w(redis://cache-01:6379/0 redis://cache-02:6379/0)
config.cache_store = :redis_cache_store, { url: cache_servers,

  connect_timeout:    30,  # Defaults to 20 seconds
  read_timeout:       0.2, # Defaults to 1 second
  write_timeout:      0.2, # Defaults to 1 second
  reconnect_attempts: 1,   # Defaults to 0

  error_handler: -> (method:, returning:, exception:) {
    # Report errors to Sentry as warnings
    Raven.capture_exception exception, level: 'warning',
      tags: { method: method, returning: returning }
  }
}

More configuration examples:

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# Defaults to `redis://localhost:6379/0`
config.cache_store = :redis_cache_store

# Supports all common cache store options (:namespace, :compress,
# :compress_threshold, :expires_in, :race_condition_tool) and all
# Redis options.
cache_password = Rails.application.secrets.redis_cache_password
config.cache_store = :redis_cache_store, driver: :hiredis,
  namespace: 'myapp-cache', compress: true, timeout: 1,
  url: "redis://:#{cache_password}@myapp-cache-1:6379/0"

# Supports Redis::Distributed with multiple hosts
config.cache_store = :redis_cache_store, driver: :hiredis
  namespace: 'myapp-cache', compress: true,
  url: %w[
    redis://myapp-cache-1:6379/0
    redis://myapp-cache-1:6380/0
    redis://myapp-cache-2:6379/0
    redis://myapp-cache-2:6380/0
    redis://myapp-cache-3:6379/0
    redis://myapp-cache-3:6380/0
  ]

# Or pass a builder block
config.cache_store = :redis_cache_store,
  namespace: 'myapp-cache', compress: true,
  redis: -> { Redis.new … }

Use :redis_store < Rails 5.2

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# Gemfile

# GitHub - redis-store/redis-rails: Redis stores for Ruby on Rails
# https://github.com/redis-store/redis-rails
gem 'redis-rails', '5.0.2'
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config.cache_store = :redis_store, { url: ENV['REDIS_URL'] }

References

[1] Caching with Rails: An Overview — Ruby on Rails Guides - https://guides.rubyonrails.org/caching_with_rails.html

[2] ActiveSupport::Cache::RedisCacheStore - https://api.rubyonrails.org/classes/ActiveSupport/Cache/RedisCacheStore.html

[3] Built-in Redis cache store by jeremy · Pull Request #31134 · rails/rails · GitHub - https://github.com/rails/rails/pull/31134

[4] New Feature on Rails 5.2: Redis Cache Store - https://blog.engineyard.com/rails-5-2-redis-cache-store

[5] Configuration Cache and Rails Session Store with Redis | by Kirill Shevchenko | Medium - https://kirillshevch.medium.com/configuration-cache-and-rails-session-store-with-redis-b3ce6f64d1fc

[6] GitHub - redis-store/redis-rails: Redis stores for Ruby on Rails - https://github.com/redis-store/redis-rails

[7] GitHub - redis-store/redis-activesupport: Redis stores for ActiveSupport - https://github.com/redis-store/redis-activesupport

[8] redis-activesupport | RubyGems.org | your community gem host - https://rubygems.org/gems/redis-activesupport

[9] redis-activesupport by redis-store - http://redis-store.org/redis-activesupport/

[10] How to Use The Redis Database in Ruby - RubyGuides - https://www.rubyguides.com/2019/04/ruby-redis/

[11] Ruby on Rails Redis installation and configuration - Hix on Rails - https://hixonrails.com/ruby-on-rails-tutorials/ruby-on-rails-redis-installation-and-configuration/

[12] GitHub - redis-store/redis-rack-cache: Redis stores for Rack::Cache - https://github.com/redis-store/redis-rack-cache

[13] GitHub - redis-store/redis-actionpack: Redis stores for ActionPack - https://github.com/redis-store/redis-actionpack

[14] Redis - https://redis.io/