A system design interview evaluates how well you can architect a large-scale application, such as a URL shortener, chat app, or food delivery platform, starting from vague requirements. Instead of writing code, you discuss components like databases, caches, load balancers, and queues, and justify every trade-off. In India, this round typically appears in hiring loops for mid-level and senior software engineers at product companies.

Build a foundation in the core building blocks first — load balancing, caching, SQL vs NoSQL databases, message queues, sharding, and replication. Then study 10–15 classic problems such as designing a URL shortener, news feed, or ticket booking system, and practise sketching one complete design every week in 40–45 minutes. Finish with mock interviews so you get comfortable thinking aloud under pressure; most working professionals need 8–12 weeks of focused preparation.

Use a repeatable framework: clarify functional and non-functional requirements, do quick capacity estimates, draw a high-level diagram of major components, and then deep-dive into two or three areas such as data storage, caching, or APIs. Close by covering bottlenecks, failure handling, and trade-offs. Interviewers evaluate structure and reasoning more than a "perfect" answer, so narrate your decisions instead of jumping straight to a diagram.

The most common system design interview questions include designing a URL shortener, a WhatsApp-style chat app, a news feed, a rate limiter, a notification system, and a BookMyShow-style ticket booking platform. Senior candidates are often asked storage-heavy designs such as a distributed file store or a video streaming service. Practising these 8–10 designs covers most of the patterns you will actually face.

System Design Interview by Alex Xu (Volumes 1 and 2) is the most widely recommended system design interview book because it walks through real problems step by step with clear diagrams. Pair it with Designing Data-Intensive Applications for deeper fundamentals on databases, replication, and consistency. Read actively — attempt each design yourself before studying the given solution.

Grokking the System Design Interview is a popular online course that breaks down roughly 15 classic design problems — URL shortening, chat systems, video streaming, and more — into repeatable templates and frameworks. It is a good starting point if you have never faced a design round and need structure quickly. Treat it as a foundation, then reinforce it by attempting designs on your own and discussing trade-offs with experienced engineers.

High level design (HLD) covers the overall system architecture — major components, databases, tech choices, and how data flows between them. Low level design (LLD) goes a layer deeper into each component: classes, responsibilities, relationships, and design patterns. In hiring processes, HLD is tested in system design rounds, while LLD is assessed through machine coding or object-oriented design rounds.

Begin with solid OOP fundamentals, then move to SOLID principles and frequently used design patterns. A practical low level design roadmap is: classes and interfaces → SOLID → patterns such as Factory, Strategy, and Observer → machine coding problems like a parking lot, Splitwise, or BookMyShow → reviews and mock rounds. Solving one timed problem every week and getting your code reviewed speeds up progress far more than passively reading theory.

The most common low level design interview questions ask you to model real-world systems in code — a parking lot, elevator system, Splitwise, BookMyShow, Snake and Ladder, chess, or a coffee vending machine. You are expected to identify the right entities, apply suitable design patterns, write clean and extensible code, and handle edge cases within 45–60 minutes.

A structured low level design course helps if you want guided feedback and a fixed plan, but it is not mandatory. Many candidates prepare using free low level design GitHub repositories that share solutions to standard machine coding problems, along with design pattern tutorials. If you are self-disciplined, combine free resources with regular peer reviews; a course is worth considering only when you are short on time or stuck without feedback.

Distributed systems architecture refers to the way multiple independent machines or services are organised to work together as one system. Common patterns include client-server, microservices, and event-driven architectures connected through networks, message queues, and shared data stores. The real challenge is keeping data consistent and the platform reliable even when individual nodes fail.

First strengthen your basics in operating systems, computer networks, and databases. Then take a structured distributed systems course or work through a standard textbook to cover replication, partitioning, consensus, and consistency models. Cement the concepts by building small projects and reading engineering blogs from companies operating at scale — the ideas only truly click when you see them applied.

Frequently asked distributed systems interview questions revolve around the CAP theorem, consistency models, replication vs partitioning, leader election and consensus algorithms like Raft and Paxos, idempotency, and handling network failures. You may also be asked to design a message queue or a rate limiter. Practise explaining trade-offs in real scenarios rather than memorising definitions.

A distributed system is any group of independent computers that cooperate over a network, while microservices is an architectural style where a single application is split into small, independently deployable services. Every microservices application is a distributed system, but distributed systems also include databases, message brokers, and storage clusters that are not microservices. In short, microservices are one popular way of building distributed systems.

Start by learning the standard scalability building blocks — load balancers, caches, CDNs, SQL and NoSQL databases, message queues, and sharding. Then study the high level design of products you already use, such as WhatsApp, Uber, or Netflix, through engineering blogs, and practise drawing a complete architecture for one app every week. Getting your diagrams critiqued by experienced engineers helps you spot missing failure handling and trade-offs much faster.