System Design Basics — Rate Limiter

What is Rate Limiter? How does it work? and What role it plays in System Design and Architecture

Published in

Javarevisited

7 min read1 day ago

Hello guys, if you are preparing for System Design Interview then you may have come across Rate Limiter, one of the essential Software architecture components along with API Gateway, Load Balancers, Distributed Caches etc.

It is also one of the popular System Design interview topic and many of my friends and readers have told me that Rate limiting algorithms and concepts are often asked on interviews.

In today’s high traffic, distributed system architecture where applications and services interact with many users and systems, maintaining stability and preventing abuse are paramount concerns.

And Rate Limiting helps with that.

Imagine we have a service which is receiving a huge number of requests, but it can only serve a limited number of requests per second. To handle this problem we would need some kind of throttling or rate limiting mechanism that would allow only a certain number of requests so our service can respond to all of them.

A rate limiter, at a high-level, limits the number of events an entity (user, device, IP, etc.) can perform in a particular time window.

In the past, I have shared best System Design courses, books, websites, newsletters, cheat sheets, mock interviews, blogs, tips, System Design github repos, and 100+ System Design Interview Questions and Problems and today I am going to share about Rate Limiter.

In other words, a Rate limiter is a mechanism used in software systems and network communications to control the rate at which requests or operations are performed.

It’s designed to prevent overuse of resources, protect systems from being overwhelmed, and ensure fair usage among multiple users or clients. It can be applied at various levels like application, API gateway, or network layer.

Rate limiters are crucial for maintaining system stability, ensuring service quality, and managing resources effectively in distributed systems and high-traffic applications.

By the way, if you are preparing for System design interviews and want to learn System Design in a limited time then you can also checkout sites like ByteByteGo, Design Guru, Exponent, Educative and Udemy which have many great System design courses

Similar, while answering System design questions you can also follow a System design template like this from DesignGuru to articulate your answer better in a limited time.

Following this template is actually one of the best thing you can do to start your preparation for any system design interview.

What is a Rate Limiter?

A rate limiter is a mechanism used in computing to control the rate at which certain operations or requests are allowed. It is commonly employed in various applications and systems to prevent abuse, protect resources, and maintain stability.

The basic idea behind a rate limiter is to restrict the number of requests or operations that a user or system can perform within a specified period.

This is done to prevent overloading a service, avoid unnecessary resource consumption, and protect against potential malicious activities or unintentional misuse.

Here’s a simple explanation of how a rate limiter works:

Define Limits: Specify the maximum number of requests or operations allowed within a certain time window. For example, you might allow only 100 requests per minute.
Track Usage: The rate limiter keeps track of the number of requests made by a user or system over time.
Check Limits: Before processing a new request, the rate limiter checks whether the user or system has exceeded the defined limits within the current time window.
Decision Making: If the user or system is within the allowed limits, the request is processed. Otherwise, the request might be delayed, rejected, or some other action taken, depending on the specific implementation.

And here is a nice diagram from Exponentthat shows the Rate Limiter in Action:

Rate Limiter Algorithms

There are different algorithms and strategies for implementing rate limiting, depending on the requirements and characteristics of the system. Some common Rate limiting algorithms include:

Token Bucket: Requests are granted as long as there are tokens available in a bucket. Tokens are added to the bucket at a fixed rate, and each request consumes one or more tokens.
Leaky Bucket: Similar to the token bucket, but instead of tokens, requests leak out of the bucket at a fixed rate. If the bucket overflows, excess requests may be delayed or discarded.
Sliding Window: Counts the number of requests made within a sliding time window. If the count exceeds the allowed limit, further requests are delayed or rejected.

Rate limiting is widely used in web APIs, network protocols, web servers, and various distributed systems to ensure fair usage, prevent abuse, and maintain system stability.

If you want to learn more then the Rate Limiter chapter on ByteByteGo by Alex Xu is a great resource, I learned most of my knowledge from there itself.

Here is a nice diagram from ByteByteGo which explains Rate Limiter working in simple words:

System Design Interviews Resources

And, here is the curated list of best system design books, online courses, and practice websites which you can check to better prepare for System design interviews. Most of these courses also answer questions I have shared here.

DesignGuru’s Grokking System Design Course: An interactive learning platform with hands-on exercises and real-world scenarios to strengthen your system design skills.
“System Design Interview” by Alex Xu: This book provides an in-depth exploration of system design concepts, strategies, and interview preparation tips.
“Designing Data-Intensive Applications” by Martin Kleppmann: A comprehensive guide that covers the principles and practices for designing scalable and reliable systems.
LeetCode System Design Tag: LeetCode is a popular platform for technical interview preparation. The System Design tag on LeetCode includes a variety of questions to practice.
“System Design Primer” on GitHub: A curated list of resources, including articles, books, and videos, to help you prepare for system design interviews.
Educative’s System Design Course: An interactive learning platform with hands-on exercises and real-world scenarios to strengthen your system design skills.
High Scalability Blog: A blog that features articles and case studies on the architecture of high-traffic websites and scalable systems.
YouTube Channels: Check out channels like “Gaurav Sen” and “Tech Dummies” for insightful videos on system design concepts and interview preparation.
ByteByteGo: A live book and course by Alex Xu for System design interview preparation. It contains all the content of System Design Interview book volume 1 and 2 and will be updated with volume 3 which is coming soon.
Exponent: A specialized site for interview prep especially for FAANG companies like Amazon and Google, They also have a great system design course and many other material which can help you crack FAANG interviews.

And, here is a nice system design interview cheat sheet to quickly revise essential System design concepts:

image_credit — tryExponent

Conclusion

That’s all about What is Rate Limiter and How it works. Rate Limiter is an important tool in any Software architects hand and you can put it where you want to prevent resource exhaustion.

It’s also one of the essential concepts to learn for a System design interview. Many companies also ask about designing an API Rate Limiter. I mean you may be asked to design an API Rate Limiter which will throttle users based upon the number of the requests they are sending.

Remember, the interviewer is not just looking for the perfect design, but assessing your approach to problem-solving, your technical knowledge, and your ability to make reasoned decisions under constraints.

Other System Design Articles and Resources you may like

Thanks for reading this article so far. If you like these system design interview tips then please share with your friends and colleagues. If you have any questions feel free to ask in comments.

P. S. — By the way, DesignGuru.io also have many other Grokking courses to prepare for essential coding interview topics like OOP Design, System Design, Dynamic Programming etc and you can get access to all of their courses for a big discount by joining their All course bundle. You can also use code GURU to get 30% discount.

All Courses

Buy all courses together to save 35% and have lifetime access.

designgurus.org