Design a mobile news feed like Instagram
PremiumMobile systemEasy
- Cursor pagination
- Image prefetching
- Video autoplay
Quick answer
This mobile system interview question asks you to design a mobile news feed like Instagram. Aim for a design that meets its requirements at the stated scale, then explain its main components, data flow and trade-offs. Interviewers want to see how you scope the problem, size it and defend each choice.
The problem
Design the mobile news feed of an app like Instagram for iOS and Android. The feed shows photo and video posts with likes and comments, and must scroll smoothly while media loads over slow networks. The hard parts are prefetching just enough media, keeping memory low and opening instantly from a cached feed.
Ranking happens on the server. Design the app side: screens, local cache, paging, media loading and data use.
What must a mobile news feed like Instagram do?
- Infinite feed: The user scrolls through posts; the next page loads before they reach the end.
- Offline open: The last 50 posts from the previous session show at once, even with no network.
How well must it do it?
- Smooth scrolling: 60 frames per second with no image decoding or disk reads on the main thread.
- Fast open: First posts on screen in under 1 second after a cold start, from the cache.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Cursor pagination
- Image prefetching
- Video autoplay
- Optimistic updates
- Offline feed cache
- Cell reuse
How you’ll practise
- Requirements
- App architecture
- Data and offline sync
- Networking and push
- Performance, battery and releases
- Wrap-up
Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.
What do interviewers look for?
In any mobile system design round.
- Clarifies the requirements before drawing anything
- Uses a few numbers that actually change the design
- Draws a clear path from the client to storage
- Picks storage and caching with reasons, not by habit
- Explains what breaks first under load and how to fix it
- States trade-offs openly instead of claiming a perfect design
Questions people ask about this interview question
- Which design type is this question?
- It is a mobile system question. You design a mobile news feed like Instagram and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Easy, so it suits engineers who are new to mobile system interviews. It is also a good warm-up before harder questions.
- What should I cover first?
- Start with the requirements: what the system must do, how well it must do it and which numbers change the design. Agree on scope with the interviewer before you design anything.
- Can I practise it for free?
- It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.
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Updated · Written by the SevyDevy team