Find My Friends — Notes

Functional

• Share live location with chosen friends/family.
• See last-known and live position on map.
• Geofence alerts.
• Temporary share links.
• Emergency SOS.

Non-functional

• Update latency < 5 s glass-to-glass.
• Battery-efficient (sparse updates when idle).
• Strong privacy controls.

Capacity

• 100M+ users; 100s of millions of small updates / hr.
• WS connections sized like chat (~100k per gateway).

Schema

• presence(user_id, lat, lng, accuracy, ts) Redis hash with TTL
• sharing(owner_id, viewer_id, since, until, precision)
• geofences(user_id, region, trigger_event)

Trade-offs

• Always-on WS vs push wakeup: WS for foreground; push notifications wake app briefly.
• Per-user channel vs presence query: channel push is timelier; periodic query is simpler.
• Server-side history = nice UX but big storage/privacy risk; default off.

Refs

• Apple Find My architecture talks (WWDC), Google Family Link / Maps share location, ByteByteGo "Design proximity / find friends".