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Memoizing Middleware

One optimization that flipper provides is a memoizing middleware. The memoizing middleware ensures that you only make one adapter call per feature per request. This means if you check the same feature over and over, it will only make one Mongo, Redis, or whatever call per feature for the length of the request.

You can use the middleware like so for Rails:

# setup default instance (perhaps in config/initializer/flipper.rb)
Flipper.configure do |config|
  config.default do

# This assumes you setup a default flipper instance using configure.
config.middleware.use Flipper::Middleware::Memoizer

Note: Be sure that the middleware is high enough up in your stack that all feature checks are wrapped.

Also Note: If you haven't setup a default instance, you can pass the instance to SetupEnv as Memoizer uses whatever is setup in the env:

config.middleware.use Flipper::Middleware::SetupEnv, -> { }
config.middleware.use Flipper::Middleware::Memoizer


The Memoizer middleware also supports a few options. Use either preload or preload_all, not both.

  • :preload - An Array of feature names (Symbol) to preload for every request. Useful if you have features that are used on every endpoint. preload uses Adapter#get_multi to attempt to load the features in one network call instead of N+1 network calls.
    config.middleware.use Flipper::Middleware::Memoizer,
      preload: [:stats, :search, :some_feature]
  • :preload_all - A Boolean value (default: false) of whether or not all features should be preloaded. Using this results in a preload_all call with the result of Adapter#get_all. Any subsequent feature checks will be memoized and perform no network calls. I wouldn't recommend using this unless you have few features (< 100?) and nearly all of them are used on every request.
    config.middleware.use Flipper::Middleware::Memoizer,
      preload_all: true
  • :unless - A block that prevents preloading and memoization if it evaluates to true.
    # skip preloading and memoizing if path starts with /assets
    config.middleware.use Flipper::Middleware::Memoizer,
      unless: ->(request) { request.path.start_with?("/assets") }

Cache Adapters

Cache adapters allow you to cache adapter calls for longer than a single request and should be used alongside the memoization middleware to add another caching layer.


Dalli is a high performance pure Ruby client for accessing memcached servers.

Example using the Dalli cache adapter with the Memory adapter and a TTL of 600 seconds:

dalli_client ='localhost:11211')
memory_adapter =
adapter =, dalli_client, 600)
flipper =


Applications using Redis via the redis-rb client can take advantage of the RedisCache adapter.

Initialize RedisCache with a flipper adapter, a Redis client instance, and an optional TTL in seconds. TTL defaults to 3600 seconds.

Example using the RedisCache adapter with the Memory adapter and a TTL of 4800 seconds:

  require 'flipper/adapters/redis_cache'

  redis = ENV['REDIS_URL'])
  memory_adapter =
  adapter =, redis, 4800)
  flipper =


Rails applications can cache Flipper calls in any ActiveSupport::Cache::Store implementation.

Add this line to your application's Gemfile:

gem 'flipper-active_support_cache_store'

And then execute:

$ bundle

Or install it yourself with:

$ gem install flipper-active_support_cache_store

Example using the ActiveSupportCacheStore adapter with ActiveSupport's MemoryStore, Flipper's Memory adapter, and a TTL of 5 minutes.

require 'active_support/cache'
require 'flipper/adapters/active_support_cache_store'

memory_adapter =
cache =
adapter =, cache, expires_in: 5.minutes)
flipper =

Setting expires_in is optional and will set an expiration time on Flipper cache keys. If specified, all flipper keys will use this expires_in over the expires_in passed to your ActiveSupport cache constructor.