System design questions are a major part of the Amazon SDE 2 interview. These rounds are not just about writing code. They test whether you can think big, design systems that handle heavy traffic, and make smart decisions about performance and reliability. Amazon wants engineers who can balance trade-offs and build systems that actually work in the real world.
One of the most common questions is “Design a URL Shortening Service.” At first, it seems simple. Shortening a link sounds easy, right? But interviewers use it to see how you handle real challenges. You need to generate unique short URLs, store billions of them, make lookups fast, handle redirects, and keep the system reliable even with millions of users hitting it at once.
This question touches almost everything in system design: APIs, databases, caching, consistency, fault tolerance, and scalability. It also shows whether you can explain your design clearly, justify your choices, and think through trade-offs. Walking through it step by step proves that you are not just a coder, but a system designer ready for SDE 2 responsibilities.
Interviewer Question
Design a URL shortening service.
Question Explanation
From an interviewer’s point of view, the question “Design a URL shortening service” tests your ability to create a scalable, reliable system that handles high traffic efficiently. They want to see how you break down the problem, choose the right components (like databases, APIs, and caching), and address key challenges such as generating unique short URLs, handling redirects, and ensuring fault tolerance. It also reveals your understanding of trade-offs and your approach to designing real-world systems.
Ideal Answer
If I had to design a URL shortening service similar to Bitly, I’d start with a REST API where users can send a long URL and receive a short one in return.
The key requirement is generating a unique short code for each long URL. I’d use Base62 encoding to keep the short URLs compact. For the backend, I’d choose Node.js or Python Flask. For storage, Redis would work well for caching, and PostgreSQL or MongoDB for persistence.
To avoid collisions, I’d use an auto-incrementing ID from the database and encode it. Alternatively, for a more distributed system, I could use a UUID and then encode it. For redirects, the system would look up the short code in the database and return a 301 redirect to the original URL.
For scalability, I’d place the service behind a load balancer and leverage CDN caching for popular links. For analytics, I’d log each redirect event using a system like Kafka and process that data asynchronously.
My role would focus on designing the API endpoints, defining the database schema for mapping short codes to long URLs, and ensuring the service is reliable and fast.
Designing a URL shortening service may seem small at first, but it touches almost every aspect of system design, from APIs and databases to caching, fault tolerance, and scalability. Explaining your thought process clearly shows that you can tackle real-world engineering problems, make smart trade-offs, and communicate like a senior engineer.
This is exactly the kind of preparation CareerXcelerator focuses on. With CareerXcelerator, you get hands-on practice with system design questions, role-specific interview prep, real-world scenarios, and mock interviews that mirror Amazon SDE 2 expectations. You also get guidance on building ATS-friendly resumes that help you stand out to recruiters. You not only learn how to solve problems but also how to explain your solutions step by step, building the confidence and skills to ace your interview and land your dream job.
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