HTTP Request Rate Limiter for Rack Applications

This is [Rack][] middleware that provides logic for rate-limiting incoming HTTP requests to Rack applications. You can use ‘Rack::Throttle` with any Ruby web framework based on Rack, including with Ruby on Rails 3.0 and with Sinatra.

Features

  • Throttles a Rack application by enforcing a minimum time interval between subsequent HTTP requests from a particular client, as well as by defining a maximum number of allowed HTTP requests per a given time period (per minute, hourly, or daily).

  • Compatible with any Rack application and any Rack-based framework.

  • Stores rate-limiting counters in any key/value store implementation that responds to ‘#[]`/`#[]=` (like Ruby’s hashes) or to ‘#get`/`#set` (like memcached or Redis).

  • Compatible with the [gdbm][] binding included in Ruby’s standard library.

  • Compatible with the [memcached][], [memcache-client][], [memcache][] and

    redis][

    gems.

  • Compatible with [Heroku][]‘s [memcached add-on][Heroku memcache] (currently available as a free beta service).

  • Compatible with Ruby 1.8.7 & 1.9

Examples

### Adding throttling to a Rails 3.x application

# config/application.rb
require 'rack/throttle'

class Application < Rails::Application
  config.middleware.use Rack::Throttle::Interval
end

### Adding throttling to a Sinatra application

#!/usr/bin/env ruby -rubygems
require 'sinatra'
require 'rack/throttle'

use Rack::Throttle::Interval

get('/hello') { "Hello, world!\n" }

### Adding throttling to a Rackup application

#!/usr/bin/env rackup
require 'rack/throttle'

use Rack::Throttle::Interval

run lambda { |env| [200, {'Content-Type' => 'text/plain'}, "Hello, world!\n"] }

### Enforcing a minimum 3-second interval between requests

use Rack::Throttle::Interval, :min => 3.0

### Allowing a maximum of 60 requests per minute

use Rack::Throttle::Minute,   :max => 60

### Allowing a maximum of 100 requests per hour

use Rack::Throttle::Hourly,   :max => 100

### Allowing a maximum of 1,000 requests per day

use Rack::Throttle::Daily,    :max => 1000

### Combining various throttling constraints into one overall policy

use Rack::Throttle::Daily,    :max => 1000  # requests
use Rack::Throttle::Hourly,   :max => 100   # requests
use Rack::Throttle::Hourly,   :max => 60    # requests
use Rack::Throttle::Interval, :min => 3.0   # seconds

### Storing the rate-limiting counters in a GDBM database

require 'gdbm'

use Rack::Throttle::Interval, :cache => GDBM.new('tmp/throttle.db')

### Storing the rate-limiting counters on a Memcached server

require 'memcached'

use Rack::Throttle::Interval, :cache => Memcached.new, :key_prefix => :throttle

### Storing the rate-limiting counters on a Redis server

require 'redis'

use Rack::Throttle::Interval, :cache => Redis.new, :key_prefix => :throttle

Throttling Strategies

‘Rack::Throttle` supports three built-in throttling strategies:

  • ‘Rack::Throttle::Interval`: Throttles the application by enforcing a minimum interval (by default, 1 second) between subsequent HTTP requests.

  • ‘Rack::Throttle::Minute`: Throttles the application by defining a maximum number of allowed HTTP requests per minute (by default, 60 requests per minute, which works out to an average of 1 request per second).

  • ‘Rack::Throttle::Hourly`: Throttles the application by defining a maximum number of allowed HTTP requests per hour (by default, 3,600 requests per 60 minutes, which works out to an average of 1 request per second).

  • ‘Rack::Throttle::Daily`: Throttles the application by defining a maximum number of allowed HTTP requests per day (by default, 86,400 requests per 24 hours, which works out to an average of 1 request per second).

You can fully customize the implementation details of any of these strategies by simply subclassing one of the aforementioned default implementations. And, of course, should your application-specific requirements be significantly more complex than what we’ve provided for, you can also define entirely new kinds of throttling strategies by subclassing the ‘Rack::Throttle::Limiter` base class directly.

HTTP Client Identification

The rate-limiting counters stored and maintained by ‘Rack::Throttle` are keyed to unique HTTP clients.

By default, HTTP clients are uniquely identified by their IP address as returned by ‘Rack::Request#ip`. If you wish to instead use a more granular, application-specific identifier such as a session key or a user account name, you need only subclass a throttling strategy implementation and override the `#client_identifier` method.

HTTP Response Codes and Headers

### 403 Forbidden (Rate Limit Exceeded)

When a client exceeds their rate limit, ‘Rack::Throttle` by default returns a “403 Forbidden” response with an associated “Rate Limit Exceeded” message in the response body.

An HTTP 403 response means that the server understood the request, but is refusing to respond to it and an accompanying message will explain why. This indicates an error on the client’s part in exceeding the rate limits outlined in the acceptable use policy for the site, service, or API.

### 503 Service Unavailable (Rate Limit Exceeded)

However, there exists a widespread practice of instead returning a “503 Service Unavailable” response when a client exceeds the set rate limits. This is technically dubious because it indicates an error on the server’s part, which is certainly not the case with rate limiting - it was the client that committed the oops, not the server.

An HTTP 503 response would be correct in situations where the server was genuinely overloaded and couldn’t handle more requests, but for rate limiting an HTTP 403 response is more appropriate. Nonetheless, if you think otherwise, ‘Rack::Throttle` does allow you to override the returned HTTP status code by passing in a `:code => 503` option when constructing a `Rack::Throttle::Limiter` instance.

Documentation

<datagraph.rubyforge.org/rack-throttle/>

Dependencies

Installation

The recommended installation method is via [RubyGems](rubygems.org/). To install the latest official release of the gem, do:

% [sudo] gem install rack-throttle

Download

To get a local working copy of the development repository, do:

% git clone git://github.com/datagraph/rack-throttle.git

Alternatively, you can download the latest development version as a tarball as follows:

% wget http://github.com/datagraph/rack-throttle/tarball/master

Authors

License

‘Rack::Throttle` is free and unencumbered public domain software. For more information, see <unlicense.org/> or the accompanying UNLICENSE file.

[Rack]: rack.rubyforge.org/ [gdbm]: ruby-doc.org/stdlib/libdoc/gdbm/rdoc/classes/GDBM.html [memcached]: rubygems.org/gems/memcached [memcache-client]: rubygems.org/gems/memcache-client [memcache]: rubygems.org/gems/memcache [redis]: rubygems.org/gems/redis [Heroku]: heroku.com/ [Heroku memcache]: docs.heroku.com/memcache