FrameworkAndroid + iOS
Mobile system design interview: the framework and every case study
Mobile rounds test the client: local storage, networking, background work, offline behavior, battery, and failure handling. There are no load balancers and no sharding. Each case study follows the same five steps.
- Clarify requirements: functional, non-functional, and what is out of scope.
- Draw the client architecture: UI, state holder, repository, local database, network.
- Define the data model and API: including the IDs that make retries safe.
- Go deep on the hard part: the send path, sync, caching, or ordering.
- Cover failure, offline and rollout: what breaks, and how you would ship it.
How a 45-minute round is spent
An example split. Companies vary, but the hard part always gets the largest share.
- Requirements5 min
- API and data model8 min
- Client architecture10 min
- The hard part17 min
- Failure, offline, rollout5 min
Case studies
Each one covers Android and iOS, with failure modes and what to say at each level.
- Design a chat appOutbox, idempotent sends, WebSocket and push sync.Read now
- Design a news feedPagination, optimistic writes, cache invalidation.Read now
- Design photo backup and file syncResumable uploads, block-level sync, conflicts.Read now
- Design a pagination libraryLibrary API, generics, request prioritization.Read now
- Design an image loading libraryMemory and disk caches, decoding, cancellation.Read now
- Design a hotel or ride booking appHolds, time sync, payments, search.Read now
- Design a stock ticker appStreaming updates, buffered UI, always-online.Read now
- Design a video streaming appPrefetching, adaptive bitrate, playback state.Read now
- Design an analytics SDKBatching, persistence, privacy, versioning.Read now
- Design a push notification SDKToken lifecycle, delivery, deep links.Read now
Guides
Cross-cutting guides that tie the case studies together.
- Staff-level mobile system design: what the round testsHow staff answers differ from senior ones, what interviewers can observe, and a four-week practice plan.Read now
- Offline-first mobile system design: one model, six case studiesThe official offline-first model applied to chat, feed, upload, booking, analytics and push.Read now
- Native vs cross-platform: write the decision recordA staff-level ADR for a framework bet: criteria, the assumption that flips it, migration, parity tests, orphaned libraries, rollback, and a free template.Read now
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