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Rate Limiting With Rack Throttle In Rails 7

Published: Mar 5, 2022

Last updated: Mar 5, 2022

Rate-limiting is a requirement of all good APIs to ensure we prevent abuse.

This post will focus on the rack-throttle gem and how it can be used with Redis to set up rules for rate-limiting.

Source code can be found here


  1. Basic familiarity with setting up a new Rails project.
  2. Basic familiarity with Redis.

Getting started

We will use Rails to initialize the project demo-rack-throttle-redis-simple:

# Create project $ rails new demo-rack-throttle-redis-simple $ cd demo-rack-throttle-redis-simple # Install the required gem $ bundler add rack-throttle # Scaffold a route to test against $ bin/rails g controller hello index

At this stage, our project is ready to update configuration.

Setting up our configuration

We will add some basic rules and remove the default forgery protection in the config/application.rb file:

require_relative 'boot' require 'rails/all' require 'rack/throttle' require 'redis' # Require the gems listed in Gemfile, including any gems # you've limited to :test, :development, or :production. Bundler.require(*Rails.groups) module DemoRackThrottleRedisSimple class Application < Rails::Application # Initialize configuration defaults for originally generated Rails version. config.load_defaults 7.0 # Set this off so we can ping the endpoint config.action_controller.default_protect_from_forgery = false if ENV['RAILS_ENV'] == 'development' # Setting rules and configuration for our `rack-throttle` middleware. rules = [ { method: 'POST', limit: 5 }, { method: 'GET', limit: 10 }, { method: 'GET', path: '/hello', limit: 1 } ] default = 10 config.middleware.use Rack::Throttle::Rules, cache:, rules: rules, default: default end end

Here we are setting baseline rules for our application. We are setting the rules to be an array of hashes. Each hash will have a method and a limit value.

In particular, the third rule for path /hello will override the GET limit to 1 which we will see in the demonstration later.

Setting up our routes

Update config/routes.rb:

Rails.application.routes.draw do resources :hello, only: [:index] # Define your application routes per the DSL in # Defines the root path route ("/") # root "articles#index" end

This will enable a GET request at /hello.

Setting up our controller

Update app/controllers/hello_controller.rb:

class HelloController < ApplicationController def index render json: { message: 'Hello, World!' } end end

We will simply send a Hello, World! message back to the client if we are not rate-limited.

Testing our rate limiting

Start a rails server with rails s.

At first, I will be using ab (ApacheBench) to test our rate-limiting, but any tool will work.

Running 6 requests at the same time will result in a 429 response for 5 of the request. See the following:

$ ab -n 6 http://localhost:3000/hello This is ApacheBench, Version 2.3 <$Revision: 1879490 $> Copyright 1996 Adam Twiss, Zeus Technology Ltd, Licensed to The Apache Software Foundation, Benchmarking localhost (be patient).....done Server Software: Server Hostname: localhost Server Port: 3000 Document Path: /hello Document Length: 27 bytes Concurrency Level: 1 Time taken for tests: 0.080 seconds Complete requests: 6 Failed requests: 5 (Connect: 0, Receive: 0, Length: 5, Exceptions: 0) Non-2xx responses: 5 Total transferred: 1698 bytes HTML transferred: 122 bytes Requests per second: 74.61 [#/sec] (mean) Time per request: 13.403 [ms] (mean) Time per request: 13.403 [ms] (mean, across all concurrent requests) Transfer rate: 20.62 [Kbytes/sec] received Connection Times (ms) min mean[+/-sd] median max Connect: 0 0 0.2 0 1 Processing: 10 13 4.3 11 21 Waiting: 10 13 4.3 11 21 Total: 10 13 4.4 11 22 Percentage of the requests served within a certain time (ms) 50% 11 66% 11 75% 15 80% 15 90% 22 95% 22 98% 22 99% 22 100% 22 (longest request)

The above tells us that we had 5 failed requests.

If you check the Rails server logs, you will see something similar to the following:

Started GET "/hello" for ::1 at 2022-03-02 16:56:06 +1000 Processing by HelloController#index as */* Completed 200 OK in 1ms (Views: 0.2ms | ActiveRecord: 0.0ms | Allocations: 114) Started GET "/hello" for ::1 at 2022-03-02 16:56:06 +1000 Started GET "/hello" for ::1 at 2022-03-02 16:56:06 +1000 Started GET "/hello" for ::1 at 2022-03-02 16:56:06 +1000 Started GET "/hello" for ::1 at 2022-03-02 16:56:06 +1000 Started GET "/hello" for ::1 at 2022-03-02 16:56:06 +1000

The last 5 requests did not complete.

Seeing the Redis cache in action

To see our throttling as it happens, we can open another terminal and run redis-cli monitor.

Do so and re-run the ab command above. You will see logs similar to the following for the monitor:

$ redis-cli monitor 1646204030.703184 [0] "get" "throttle:::1_GET_/hello:2022-03-02T16:53:50" 1646204030.703369 [0] "set" "throttle:::1_GET_/hello:2022-03-02T16:53:50" "1" 1646204030.715999 [0] "get" "throttle:::1_GET_/hello:2022-03-02T16:53:50" 1646204030.716196 [0] "set" "throttle:::1_GET_/hello:2022-03-02T16:53:50" "2" 1646204030.726116 [0] "get" "throttle:::1_GET_/hello:2022-03-02T16:53:50" 1646204030.726411 [0] "set" "throttle:::1_GET_/hello:2022-03-02T16:53:50" "3" 1646204030.743322 [0] "get" "throttle:::1_GET_/hello:2022-03-02T16:53:50" 1646204030.745936 [0] "set" "throttle:::1_GET_/hello:2022-03-02T16:53:50" "4" 1646204030.760111 [0] "get" "throttle:::1_GET_/hello:2022-03-02T16:53:50" 1646204030.760280 [0] "set" "throttle:::1_GET_/hello:2022-03-02T16:53:50" "5" 1646204030.773758 [0] "get" "throttle:::1_GET_/hello:2022-03-02T16:53:50" 1646204030.774029 [0] "set" "throttle:::1_GET_/hello:2022-03-02T16:53:50" "6"

We can see the /hello call being incremented each time.

A closer look with HTTPie

If we makes calls again, but this time with httpie, we can get more info on a successful request vs a rate-limited response.

# First successfuly request $ http GET localhost:3000/hello HTTP/1.1 200 OK Cache-Control: max-age=0, private, must-revalidate Content-Type: application/json; charset=utf-8 ETag: W/"8811a6f55cb434d10921bccf7108016d" Referrer-Policy: strict-origin-when-cross-origin Server-Timing: start_processing.action_controller;dur=0.152099609375, process_action.action_controller;dur=0.951904296875 Transfer-Encoding: chunked Vary: Accept X-Content-Type-Options: nosniff X-Download-Options: noopen X-Frame-Options: SAMEORIGIN X-Permitted-Cross-Domain-Policies: none X-Request-Id: 63a86723-bd98-4f4d-a8fc-86da84632c47 X-Runtime: 0.013456 X-XSS-Protection: 0 { "message": "Hello, World!" } # Second, rate-limited run within 1 second of the last $ http GET localhost:3000/hello HTTP/1.1 403 Forbidden Cache-Control: no-cache Content-Type: text/plain; charset=utf-8 Retry-After: 3600 Server-Timing: Transfer-Encoding: chunked X-Request-Id: 059ee3bd-4aa4-4578-a290-42c981711251 X-Runtime: 0.006463 Rate Limit Exceeded

We get a 403 forbidden on rate limited results.


Today we demonstrated how to set up basic rate-limiting rules with the rack-throttle gem.

In the next post, we will revisit this topic but instead using the rack-attack gem.

Resources and further reading

Photo credit: vingtcent

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Dennis O'Keeffe

  • Melbourne, Australia

Hi, I am a professional Software Engineer. Formerly of Culture Amp, UsabilityHub, Present Company and NightGuru.
I am currently working on Visibuild.


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