Design iCloud photos with multi-device sync
PremiumProduct architectureHard
- Multi device sync
- Sync tokens
- Content hash dedup
Quick answer
This product architecture interview question asks you to design iCloud photos with multi-device sync. 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 a cloud photo library like iCloud Photos with multi-device sync. Photos and videos taken on any phone, tablet or laptop upload once and appear on the user's other devices, and edits, deletes and albums stay in sync. The hard parts are dedup, conflicts from offline edits, and cheap sync for libraries of tens of thousands of items.
What must the system do?
- Upload once: A new photo or video uploads from the device that took it, resumably, so a dropped connection does not restart a 2 GB video.
- Sync everywhere: New items, edits, favourites, deletes and album changes made on one device appear on the other online devices within 1 minute.
How well must it do it?
- No data loss: Once the server acknowledges an upload, the original is durable and no sync bug may delete it.
- Convergence: After syncing, all devices of an account show the same library, whatever order the changes arrived in.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Multi device sync
- Sync tokens
- Content hash dedup
- Resumable uploads
- Conflict resolution
- Non destructive edits
How you’ll practise
- Requirements
- Core entities
- API design
- Client and server flow
- Scale and edge cases
- 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 product architecture 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 product architecture question. You design iCloud photos with multi-device sync and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Hard. It suits engineers preparing for senior interviews, where you are expected to drive the discussion and go deep on trade-offs.
- 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