Rate limiting in Ruby on Rails - Mini Project: Build & Apply

Implementing Rate Limiting in a Rails Controller

📖 Scenario: You are building a simple Rails API that serves user data. To protect your API from too many requests in a short time, you want to add rate limiting.This means limiting how many times a user can call the API within a certain time frame.

🎯 Goal: Build a Rails controller with a rate limiting mechanism that allows only 5 requests per minute per user.Use a simple in-memory store (a Ruby hash) to track request counts.

📋 What You'll Learn

Create a controller with an action that returns a JSON message

Add a configuration variable for the maximum allowed requests per minute

Implement rate limiting logic that counts requests per user IP

Return a 429 status code with a message when the limit is exceeded

💡 Why This Matters

🌍 Real World

APIs often need rate limiting to prevent abuse and ensure fair usage among users.

💼 Career

Understanding rate limiting is important for backend developers building scalable and secure web services.

1

Create a Rails controller with an action

Create a Rails controller named ApiController with an action user_data that renders JSON with { message: 'User data accessed' }.

Ruby on Rails

class ApiController < ApplicationController
  # Define user_data action
  # Your code here
end

Hint

Use render json: { message: 'User data accessed' } inside the user_data method.

2

Add a configuration variable for rate limit

Add a constant MAX_REQUESTS_PER_MINUTE set to 5 inside the ApiController class.

Ruby on Rails

class ApiController < ApplicationController
  MAX_REQUESTS_PER_MINUTE = 5

  def user_data
    render json: { message: 'User data accessed' }
  end
end
# Add the constant MAX_REQUESTS_PER_MINUTE = 5 inside the class

Hint

Define MAX_REQUESTS_PER_MINUTE = 5 inside the controller class but outside any method.

3

Implement rate limiting logic

Inside the user_data action, create a class variable @@request_counts as a hash to track requests by request.remote_ip. Increment the count for the current IP. If the count exceeds MAX_REQUESTS_PER_MINUTE, render JSON with { error: 'Rate limit exceeded' } and status 429. Otherwise, render the success message.

Ruby on Rails

class ApiController < ApplicationController
  MAX_REQUESTS_PER_MINUTE = 5
  @@request_counts = Hash.new(0)

  def user_data
    # Implement rate limiting logic here
    # Your code here
  end
end

Hint

Use request.remote_ip to get the user's IP and track counts in @@request_counts.

4

Reset request counts every minute

Add a method reset_request_counts that clears @@request_counts. Use before_action to call reset_request_counts every minute by checking if a class variable @@last_reset is more than 60 seconds ago. Initialize @@last_reset to the current time.

Ruby on Rails

class ApiController  MAX_REQUESTS_PER_MINUTE
      render json: { error: 'Rate limit exceeded' }, status: 429
    else
      render json: { message: 'User data accessed' }
    end
  end
end

Hint

Use before_action to call reset_request_counts before each request.

Reset counts if more than 60 seconds passed since last reset.

Practice

1. What is the main purpose of rate limiting in a Rails application?

easy

A. To control how often users can make requests to the server

B. To speed up database queries automatically

C. To style the user interface dynamically

D. To manage user sessions securely

Solution

1. Step 1: Understand rate limiting concept

   Rate limiting is about controlling the number of requests a user can make in a time period.

2. Step 2: Identify the main purpose in Rails context

   It helps protect the server from overload and abuse by limiting request frequency.

3. Final Answer:

   To control how often users can make requests to the server -> Option A

4. Quick Check:

   Rate limiting = controlling request frequency [OK]

Hint: Rate limiting controls request frequency to protect servers [OK]

Common Mistakes:

• Confusing rate limiting with UI styling
• Thinking it speeds up database queries
• Mixing it with session management

2. Which of the following is the correct way to configure a simple rate limit using Rack::Attack in Rails?

easy

A. Rack::Attack.throttle('req/ip', limit: 5, period: 1.minute) { |req| req.ip }

B. Rack::Attack.limit('req/ip', 5, 1.minute) { |req| req.ip }

C. Rack::Attack.throttle('req/ip', 1.minute, limit: 5) { |req| req.ip }

D. Rack::Attack.block('req/ip', limit: 5, period: 1.minute) { |req| req.ip }

Solution

1. Step 1: Recall Rack::Attack throttle syntax

   The correct method is throttle with arguments: name, limit, period, and a block returning the key.

2. Step 2: Match syntax with options

   Rack::Attack.throttle('req/ip', limit: 5, period: 1.minute) { |req| req.ip } uses throttle with named parameters limit: 5 and period: 1.minute, and block returning req.ip, which is correct.

3. Final Answer:

   Rack::Attack.throttle('req/ip', limit: 5, period: 1.minute) { |req| req.ip } -> Option A

4. Quick Check:

   Correct method and parameters = Rack::Attack.throttle('req/ip', limit: 5, period: 1.minute) { |req| req.ip } [OK]

Hint: Use throttle with named limit and period parameters [OK]

Common Mistakes:

• Using wrong method name like limit or block
• Swapping limit and period order
• Not passing a block returning the key

3. Given this Rack::Attack throttle configuration:

Rack::Attack.throttle('logins/ip', limit: 3, period: 20.seconds) { |req| req.ip if req.path == '/login' && req.post? }

What happens if a user makes 4 POST requests to '/login' within 20 seconds from the same IP?

medium

A. Only the 1st request is blocked

B. The 4th request is blocked due to rate limit

C. All 4 requests are allowed without restriction

D. The 4th request resets the limit counter

Solution

1. Step 1: Understand throttle parameters

   The limit is 3 requests per 20 seconds per IP for POST requests to '/login'.

2. Step 2: Analyze 4 POST requests from same IP

   The first 3 requests pass, the 4th exceeds the limit and is blocked.

3. Final Answer:

   The 4th request is blocked due to rate limit -> Option B

4. Quick Check:

   Requests > limit = block excess [OK]

Hint: Requests over limit within period get blocked [OK]

Common Mistakes:

• Assuming all requests pass
• Thinking limit resets on 4th request
• Confusing which requests count

4. You wrote this code to limit API requests:

Rack::Attack.throttle('api/ip', limit: 10, period: 1.minute) do |req|
  req.ip if req.path.start_with?('/api')
end

But users report no limits are applied. What is the likely problem?

medium

A. The period should be in seconds, not minutes

B. The limit value 10 is too high to trigger blocking

C. The block returns nil for non-API paths, so no key is generated for those requests

D. The method throttle is not supported in Rack::Attack

Solution

1. Step 1: Check block return value logic

   The block returns req.ip only if path starts with '/api', else returns nil.

2. Step 2: Understand throttle key generation

   If block returns nil, no key is generated and no limit applies for those requests.

3. Final Answer:

   The block returns nil for non-API paths, so no key is generated for those requests -> Option C

4. Quick Check:

   Nil key means no rate limiting applied [OK]

Hint: Block must return key for all requests to apply limits [OK]

Common Mistakes:

• Thinking limit 10 is too high
• Confusing period units
• Believing throttle method is unsupported

5. You want to limit login attempts per user email and IP address separately using Rack::Attack. Which configuration correctly applies this?

hard

A. Rack::Attack.throttle('logins/email', limit: 5, period: 1.hour) { |req| req.params['email'].presence }Rack::Attack.throttle('logins/ip', limit: 10, period: 1.hour) { |req| req.params['email'] }

B. Rack::Attack.throttle('logins/email_ip', limit: 5, period: 1.hour) { |req| req.params['email'] + req.ip }

C. Rack::Attack.throttle('logins/email', limit: 5, period: 1.hour) { |req| req.ip }Rack::Attack.throttle('logins/ip', limit: 10, period: 1.hour) { |req| req.params['email'] }

D. Rack::Attack.throttle('logins/email', limit: 5, period: 1.hour) { |req| req.params['email'] }Rack::Attack.throttle('logins/ip', limit: 10, period: 1.hour) { |req| req.ip }

Solution

1. Step 1: Understand separate throttles for email and IP

   We want one throttle keyed by email, another keyed by IP address.

2. Step 2: Match keys to correct throttle names

   Rack::Attack.throttle('logins/email', limit: 5, period: 1.hour) { |req| req.params['email'] }
   Rack::Attack.throttle('logins/ip', limit: 10, period: 1.hour) { |req| req.ip } correctly uses req.params['email'] for email throttle and req.ip for IP throttle with proper limits.

3. Final Answer:

   Rack::Attack.throttle('logins/email', limit: 5, period: 1.hour) { |req| req.params['email'] }
   Rack::Attack.throttle('logins/ip', limit: 10, period: 1.hour) { |req| req.ip } -> Option D

4. Quick Check:

   Separate keys for email and IP = Rack::Attack.throttle('logins/email', limit: 5, period: 1.hour) { |req| req.params['email'] }
   Rack::Attack.throttle('logins/ip', limit: 10, period: 1.hour) { |req| req.ip } [OK]

Hint: Use separate throttle blocks keyed by email and IP [OK]

Common Mistakes:

• Mixing email and IP keys in wrong throttles
• Concatenating email and IP as one key
• Using IP where email key is needed