Design a Google Photos–like service

Q: Design a Google Photos–like service

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Question

System Design: Google Photos–like Service (Web + Mobile)

Context

Design a large-scale consumer media service that ingests, stores, indexes, and serves billions of photos and videos across mobile and desktop. Users expect near-instant uploads, fast viewing, powerful search, easy sharing, and seamless sync across devices with strong privacy.

Assume a modern cloud environment with globally distributed users.

Scale Assumptions (to ground trade-offs)

Users: 100M MAU, 25M DAU.
Uploads per DAU: ~5 photos/day, 0.1 videos/day → ~125M photos/day, 2.5M videos/day.
Average sizes: photo 4 MB, video 50 MB.
New data/day: ~0.5 PB photos + ~125 TB videos ≈ ~0.625 PB/day.
Peak ingest: 3× daily average during regional evenings.
Read-heavy: 10× more reads than writes; p95 photo load < 200 ms from cache.

You may adjust numbers slightly if needed; justify trade-offs.

Requirements

Client upload workflows
- Mobile: background/resumable uploads, low battery/data usage, offline queue, idempotency.
- Desktop: bulk sync, folder watch, conflict resolution.
Media ingestion pipeline
- Edge upload, resumable sessions, virus/abuse scanning, metadata extraction (EXIF), deduplication via content hashes.
Storage architecture
- Object storage for originals and variants; hot/cold tiers; lifecycle policies; encryption.
Delivery
- CDN-backed delivery for images/thumbnails/video streaming; signed URLs; cache strategies.
Sharing & permissions
- Private-by-default; per-item/album ACLs; shareable links; link expiration; collaborative albums.
Search & indexing
- Filter by time/location/EXIF; text tags; face/object recognition; similarity search; privacy-preserving per-user indexes.
Thumbnail/transforms
- Multi-size thumbnails; server-side video transcoding (HLS/DASH); on-demand vs precompute trade-offs.
Sync across devices
- Delta sync; read-your-writes; notifications; conflict resolution.
Privacy & compliance
- E2E transport security; encryption at rest; data residency; GDPR/CCPA deletion; audit logging; safe content handling.
Disaster recovery

Multi-region durability; RPO/RTO targets; backups; runbooks.

Cost awareness

High-level capacity planning and monthly cost estimation; cost-reduction levers.

Deliverables

High-level architecture and key components.
API design (upload, list, get, search, share), idempotency, auth.
Data model (logical schema) for users, media, albums, ACLs, indexes.
Partitioning/sharding strategies.
Consistency vs availability choices per workflow.
Reasonable cost estimate and key optimizations.