FaradayThrottler

Configurable Faraday middleware for Ruby HTTP clients that:

• limits request rate to backend services.
• does its best to return cached or placeholder responses to clients while backend service is unavailable or slow.
• optionally uses Redis to rate-limit outgoing requests across processes and servers.

Use case

Use this gem if you want to help avoid request stampedes to your backend APIs. For example after front-end cache expiration. This middleware can help you limit the number and rate of concurrent requests to the backend, while serving useful cached or hard-coded responses back to the client when the backend is not inmediatly available.

Installation

Add this line to your application's Gemfile:

gem 'faraday_throttler'

And then execute:

$ bundle

Or install it yourself as:

$ gem install faraday_throttler

Usage

Defaults

The defaul configuration uses an in-memory lock and in-memory cache. Not suitable for multi-server deployments.

require 'faraday'
require 'faraday_throttler'

client = Faraday.new(:url => 'https://my.api.com') do |c|
 c.use(
    :throttler,
    # Allow up to 1 request every 3 seconds, per path, to backend
    rate: 3,
    # Queued requests will wait for up to 2 seconds for current in-flight request
    # to the same path.
    # If in-flight request hasn't finished after that time, return a default placeholder response.
    wait: 2
 )
 c.adapter Faraday.default_adapter
end

Make some requests:

resp = client.get('/foobar')
resp.body

The configuration above will only issue 1 request every 3 seconds to my.api.com/foobar. Requests to the same path will wait for up to 2 seconds for current in-flight request to finish.

If an in-flight request finishes within the wait period, queued requests will respond with the same data, and the data will be cached as a fallback.

If the in-flight request doesn't finish within 2 seconds (wait period), queued requests will attempt to serve a previous response from the same resource from cache.

If no matching response found in cache, a default fallback response will be used (status 204 No Content). Fallback responses can be cofigured.

Tweaking the rate and wait arguments allows you to control the rate of cached, fresh and fallback reponses.

Distributed Redis lock and cache

The defaults use in-memory lock and cache store implementations. To make the most efficient use of this gem across processes and servers, you can use Redis as a distributed lock and cache store.

require 'redis'
require 'faraday_throttler/redis_lock'
require 'faraday_throttler/redis_cache'

redis = Redis.new(uri: 'redis://my-redis-server.com:1234')

redis_lock = FaradayThrottler::RedisLock.new(redis)

# Cache entries will be available for 1 hour
redis_cache = FaradayThrottler::RedisCache.new(redis: redis, ttl: 3600)

client = Faraday.new(:url => 'https://my.api.com') do |c|
 c.use(
    :throttler,
    rate: 3,
    wait: 2,
    # Use Redis-backed lock
    lock: redis_lock,
    # Use Redis-backed cache with set expiration
    cache: redis_cache
 )
 c.adapter Faraday.default_adapter
end

Advanced usage

Most internal behaviours are split into delegate objects that you can pass as middleware arguments to override the defaults. See the details in the code.

Development

After checking out the repo, run bundle install to install dependencies. Then, run bundle exec rspec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ismasan/faraday_throttler.

To contribute with code:

1. Fork it ( http://github.com/ismasan/faraday_throttler/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request