Design a push notification system for mobile apps
PremiumMobile systemMedium
- Apns
- FCM
- Device token lifecycle
Quick answer
This mobile system interview question asks you to design a push notification system for mobile apps. 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 on-device push notification system for a company's iOS and Android apps as a shared SDK. It registers device tokens with APNs and FCM, asks for permission, shows rich notifications and opens the right screen on tap. The hard parts are token churn, permission rules on each OS and pushes that arrive late, collapsed or not at all.
What must a push notification system for mobile apps do?
- Token registration: Every install registers its APNs or FCM token and keeps the server copy current when the token changes.
- Permission: Ask for notification permission at a moment the user understands, on iOS and on Android 13 and later.
How well must it do it?
- No silent loss of reach: A token change or reinstall never leaves a user unreachable for more than one app launch.
- No duplicates: The same notification is never shown twice, even if pushed again or shown in-app.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Apns
- FCM
- Device token lifecycle
- Notification channels
- Notification permission
- Notification service extension
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 push notification system for mobile apps and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Medium. Entry-level engineers can practise it, but it expects you to reason about requirements and trade-offs, not only list components.
- 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