Backend API Design for Mobile Clients Questions

Designing backend application programming interfaces specifically for mobile clients, addressing mobile device constraints, network variability, and cross platform compatibility. Core concerns include bandwidth optimization techniques such as pagination, selective field queries, delta responses, efficient serialization formats, and compression; response shape and protocol trade offs including representational state transfer versus GraphQL; versioning and backward compatibility strategies for long lived mobile applications; error handling, retry semantics, and user friendly error surfaces appropriate for intermittent connectivity; rate limiting, throttling, and quota management; real time synchronization patterns including polling, web sockets, and server sent events; caching, offline support, data synchronization, conflict resolution, and optimistic updates; authentication and token refresh strategies, security and privacy considerations; and monitoring, telemetry, testing, and deployment practices that minimize breaking changes for mobile clients.

EasyTechnical

49 practiced

Explain pagination strategies suitable for mobile clients: offset-based pagination, cursor/keyset pagination, time-based feeds, and prefetching. For each strategy describe impact on bandwidth, server cost (OFFSET vs seek), consistency when new items are inserted or removed, and recommend an approach for an infinite-scroll mobile feed. Include how you would encode cursors and handle max page sizes.

EasyTechnical

43 practiced

Describe sparse fieldsets / selective field queries and how mobile clients can request only needed fields to save bandwidth. Show short examples of how a client might request fields in REST and GraphQL.

REST example:GET /articles?fields=title,author,thumbnail

GraphQL example:{ article(id:123){ title author { name } thumbnail }}

Explain server-side caveats (computed fields, default fields, and caching implications).

EasyTechnical

51 practiced

Describe a secure refresh token flow for mobile apps. Explain the roles of access and refresh tokens, refresh token rotation, secure storage on device, refresh endpoint behavior, refresh failure handling (forced re-auth), and common pitfalls such as long-lived refresh tokens or refresh token reuse.

MediumSystem Design

48 practiced

Design API endpoints and mobile client behavior for uploading large photos/videos: support resumable uploads, background transfer on iOS/Android, client-side compression, chunking protocols, integrity checks (checksums), resume tokens, and server-side assembly. Provide sample endpoint names and describe how the client handles network interruptions and power constraints.

MediumTechnical

43 practiced

For a mobile app that needs near-real-time updates, describe criteria for choosing between push notifications, WebSockets, and Server-Sent Events (SSE). Address background delivery constraints (especially iOS), battery and data trade-offs, delivery guarantees, complexity, message sizes, and fallback strategies when a persistent connection is unavailable.

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