As you become more experienced as a software engineer, your job isn't just writing code anymore. You also have to design big systems that work well even when millions of people use them. System design interviews are a critical part of hiring not just for software engineers but also for engineering leadership roles like tech leads and engineering managers.
These interviews often determine whether you secure a high-paying position, as they assess your ability to make architectural decisions that impact scalability, reliability, and maintainability.
Unlike coding interviews, system design interviews take known, large, and complex systems like YouTube or WhatsApp and ask you to create a plan for how you would design them.
Here's why good system design matters:
Scalability: Making sure the system can handle more and more users without slowing down.
Reliability: Designing the system to keep working even if parts break or fail.
Efficiency: Making the system fast without wasting resources.
Maintainability: Building the system so it's easy to update and fix in the future.
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System design, explained ridiculously simply. Finally, make sense of system design and pass your next interview!
What you can expect in the interview
System design interviews test how well you can design large-scale, distributed systems under real-world constraints. These interviews are common in mid to senior-level software engineering roles, especially at companies that build high-traffic applications.
A typical system design interview lasts 45 to 60 minutes and follows this structure:
The interviewer presents an open-ended problem, such as designing a URL shortener, a messaging system, or a video streaming platform.
You clarify requirements and constraints before jumping into the design.
You outline the high-level architecture, defining key components and their interactions.
You discuss database choices, storage strategies, scaling techniques, and potential bottlenecks.
You analyze trade-offs and failure scenarios, demonstrating how the system can handle growth and unexpected failures.
What interviewers look for:
Can you break down a large problem into smaller, manageable parts?
Do you understand how to scale systems efficiently?
Can you justify your design decisions based on trade-offs and constraints?
Are you considering real-world limitations such as network failures and database consistency?
A good system design interview response is structured, covers the key components of the system, and adapts to follow-up questions effectively.
The Framework to approach any System Design interview
Many candidates struggle in system design interviews because they jump into solutions too quickly without structuring their thoughts. Instead, follow this five-step framework to keep your response organized and clear.
Step 1: Understand what you’re asked to build
Before you start designing anything, make sure you know exactly what you are building. Ask questions like:
What does this system need to do? (e.g., send messages, store photos, process payments)
What is most important - speed, reliability, or handling lots of users?
How many users should it support? Thousands, millions, or more?
Are there limits on things like cost, security, or storage?
Once you understand the requirements, write them down so you don’t forget anything.
Step 2: Identify the main parts
Now that you know what you’re building, think about the key components the system will need. Most systems have:
Users – People using the system through a website, app, or API
Load balancers - Distribute traffic across multiple servers
Servers – Computers that process user requests
Databases – Where information is stored
Caching – A way to make things faster by storing frequently used data
Message Queues – Used to handle background tasks efficiently
Draw a simple diagram to show how these parts connect.
Step 3: Choose the right database
A system usually needs a place to store data. You need to decide:
SQL or NoSQL?
SQL (structured, organized data like bank transactions)
NoSQL (flexible, good for big, fast-growing data like social media posts)
How do we scale it?
Split data across multiple servers (sharding)
Make copies of data for reliability (replication)
If the system needs fast search, use indexing to speed things up.
Step 4: Make sure it can scale
If the system gets more users, it needs to handle high traffic without slowing down. Some ways to do this:
Load balancing – Distribute user requests across multiple servers
Caching – Store commonly requested data so it loads faster
Database sharding – Split large data into smaller chunks across different servers
Message queues – Process background tasks efficiently (e.g., sending emails without slowing the system)
Step 5: Plan for failures
Things will go wrong, so design your system to recover quickly:
Use backups – Have extra copies of important data
Redundant servers – If one server crashes, another takes over
Retries & circuit breakers – If something fails, try again or switch to a backup
Rate limiting – Prevent too many requests at once so the system doesn’t crash
Final thoughts
I appreciate that this is a lot to take in. System design can feel overwhelming at first. But don't worry! My goal is to break down each and every concept I’ve mentioned here and more in this newsletter, making it easier to understand over time.
If you want to get better at system design, start reading about some of the ideas mentioned in this post that you’re not very familiar with.
Remember the five-step framework in your next interview:
Understand what you’re asked to build
Identify the main parts
Choose the right database
Make sure it can scale
Plan for failures
System design interviews test your ability to think critically, analyze trade-offs, and communicate effectively.
There is a lot of knowledge required to be able to do this, but that’s exactly what this newsletter is for.
So stick around. I’ll be breaking System Design concepts down one by one!
