Android System Design Interview Questions

"Design Instagram's feed" isn't a request to rebuild Instagram in 45 minutes. It's an invitation to show how you clarify requirements, choose a client architecture, handle network and storage constraints, and reason about trade-offs, while communicating clearly.

A framework for the interview

Step 1: Clarify

• Functional: core features for this interview (for example: view feed, like, comment, post photo).
• Non-functional: offline support? Real-time? Scale (users, items per screen)? Low-end devices? Battery and data constraints?
• Out of scope: confirm what you'll skip (for example the ranking algorithm and server internals).

Step 2: API and data models

GET  /feed?cursor={cursor}&limit=20      → { items: [Post], nextCursor }
POST /posts/{id}/like                    → { liked: true, likeCount }   (idempotent)
POST /posts  (multipart: image + caption) → Post
Post { id, author{id,name,avatarUrl}, imageUrl, caption, likeCount, likedByMe, createdAt }

Mention cursor-based pagination (stable under inserts), idempotency for actions, and image URLs with size variants.

Step 3: Client architecture

Step 4: Common deep dives

Worked example prompts

Step 5: Trade-offs to volunteer

• Consistency vs responsiveness (optimistic UI).
• Real-time freshness vs battery and data.
• Offline capability vs complexity and storage.
• Modularization vs speed for a small team.

Frequently asked questions

Conclusion

Ace mobile system design by clarifying constraints, defining APIs and models, presenting a clear client architecture, going deep on offline, pagination, real-time and media, and volunteering trade-offs, all while thinking out loud.

Next step: prepare the whole senior loop with How to Prepare for a Senior Android Developer Interview.