System Design
System Design for Beginners: A Practical Guide
System design interviews feel intimidating until you realise they follow predictable patterns. Here is a practical framework to approach any design problem with confidence.
System design interviews are the gatekeeper for senior engineering roles. Unlike coding interviews, there is no single correct answer. The interviewer is evaluating your process: how you handle ambiguity, make trade-offs, and communicate your reasoning. This guide walks through a repeatable framework.
Key takeaways
- Use the CRAQ framework: Clarify, Rough estimate, Abstract design, Key components.
- Spend the first 5 minutes asking questions, not drawing boxes.
- Learn the trade-offs of each building block, not just its purpose.
- Master 5 classic designs: URL shortener, chat, Instagram, Uber, YouTube.
- There is no perfect design — only trade-offs you can explain.
The framework: CRAQ Method
Every system design question can be approached with the same structure: Clarify Requirements, Rough Estimate, Abstract Design, dive into Key Components. This keeps the conversation organised and ensures you do not miss critical aspects.
Start by clarifying the requirements. What are the features? How many users? What is the read-to-write ratio? What latency is acceptable? Most candidates start designing too early — the first 5 minutes should be all questions.
- Clarify: Features, users scale, read/write ratio, latency requirements
- Rough estimate: QPS, storage needs, bandwidth estimates
- Abstract design: Load balancer → API → Service → DB → Cache
- Key components: Dive into 2-3 areas that matter most
Building blocks you must know
Load balancers, caching strategies, database sharding, CDNs, message queues, and consistent hashing. These are the building blocks that appear in every system design solution. You do not need to implement them — you need to know when to use each one and what trade-off each choice carries.
For example, caching seems straightforward until someone asks: what happens when the cache is stale? What is your invalidation strategy? Cache-aside vs write-through vs write-behind — each has a different consistency guarantee and performance profile.
Practice these 5 designs
Master these five system designs: URL shortener (simple, teaches hashing and redirection), chat system (real-time, teaches WebSockets and message ordering), design Instagram (media-heavy, teaches CDN and feed generation), design Uber (location-based, teaches geospatial indexing and dispatch), and design YouTube (video-heavy, teaches transcoding pipeline and CDN strategy).
Each of these teaches a different architectural lesson. Once you can design all five confidently, you have the building blocks for 90% of system design questions.
FAQ
Frequently asked questions
Do I need system design for junior roles?
For junior roles, expect simpler designs focused on a single service. For senior roles (3+ years), expect distributed system discussions.
How do I estimate storage and QPS?
Round numbers are fine. 1 million DAU, 10 requests per user per day, ~115 QPS. Storage: estimate per-record size and multiply.
Should I draw on a whiteboard or use text?
For remote interviews, use a simple drawing tool or clearly describe components. The reasoning matters more than the diagram.