If you are a developer, you’ve probably noticed that system design interviews feel harder than coding interviews.
That’s because system design is not about syntax or frameworks.
It’s about how you think before you build.
This post explains system design in the simplest way possible—using a real-world analogy.
What Is System Design? (In Simple Words)
System design is the process of planning how a system should be built before writing code.
A good system:
- Solves the right problem
- Works reliably
- Can grow in the future
- Is easy to fix when something breaks
System design helps you answer:
What should we build, where should it live, and how should everything work together?
The Two Sides of System Design
System design has two major parts:
- Design decisions (planning)
- System qualities (real-world expectations)
Let’s look at them one by one.
Part 1: Design Decisions
1. Requirements – What are we building?
Before anything else, you must be clear about the requirements.
This includes:
- What features are needed
- What is NOT needed
- Any constraints (users, performance, cost)
Without clear requirements:
- You build unnecessary features
- Or miss important ones
2. Architecture – Where does everything belong?
Architecture decides:
- How the system is divided into parts
- Where each responsibility lives
- How data flows between components
Good architecture ensures:
- Clear separation of concerns
- Easier scaling
- Fewer future rewrites
3. Interfaces – How do parts talk to each other?
Interfaces define:
- API contracts
- UI interactions
- Input and output formats
Good interfaces:
- Reduce dependency between components
- Make teams work independently
- Make changes safer
Part 2: System Qualities (Non-Functional Requirements)
Even if a system works today, it must survive real-world usage.
Scalability – Can it grow?
A system should handle:
- More users
- More data
- More traffic
Growth can happen by:
- Scaling up (stronger machines)
- Scaling out (more machines)
Security – Is it safe?
Security protects:
- User data
- Business logic
- Trust
An insecure system is a broken system.
Maintainability – Can we fix it easily?
Things will break:
- Bugs
- Infrastructure issues
- Changing requirements
A maintainable system is:
- Easy to debug
- Easy to modify
- Easy to extend
A Simple Analogy: Designing a Villa
Now let’s connect everything with a real-life example.
Step 1: Requirements
You don’t say:
“Build me a house.”
You say:
- I need 2 bedrooms
- A kitchen and balcony
- Parking space
- A terrace
These are clear requirements.
Step 2: Architecture (Placement)
Now you decide where things go.
- Parking should be easily accessible
- Guest room should not be hidden inside the house
- Kitchen should be centrally located
This is architecture—logical placement for smooth flow.
Step 3: Interfaces (Details)
Next come the details:
- Furniture size
- Kitchen layout
- Space for appliances
These are like:
- UI components
- API request/response formats
They define how users interact with the system.
Step 4: System Qualities
Finally, the villa must handle real-life situations.
Scalability
Can you add another floor later?Security
Are there locks, gates, and cameras?Maintainability
If a pipe leaks, can it be fixed without breaking walls?
Why Developers Should Care
You don’t need to be a “system architect” to do system design.
If you:
- Design APIs
- Structure frontend applications
- Decide where logic lives
You are already doing system design.
The goal is to do it intentionally and clearly.
The next step is learning how systems evolve when they grow—from small setups to large-scale platforms.
Reference
This post is inspired by the “Introduction to System Design” content by Chirag Goel.
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