CHAPTER 06

Enterprise Real-World System Architecture Case Studies

Translating architectural primitives into battle-tested end-to-end production systems capable of serving hundreds of millions of users.

1. High-Scale Global Chat Platform (WhatsApp / Discord Level)

10M+ Concurrent WebSockets

Stateful Connection Tier: Go or Erlang/Elixir BEAM lightweight process nodes maintaining long-lived WebSocket connections. Connection state (User ID \(\to\) Server Node IP) registered in Redis Cluster with TTL heartbeats.

Storage Layer (ScyllaDB / Cassandra): Partition Key: channel_id, Clustering Key: message_id (TimeUUID). Enables \(O(1)\) append writes and fast range scans for message history pagination.

Push Notifications & Offline Messages: If recipient node is offline, message is pushed to Kafka offline-notifications topic, processed by background workers dispatching to FCM (Android) and APNs (iOS).

2. High-Concurrency Ticket Booking Engine (BookMyShow / Ticketmaster)

Zero Overbooking Guarantee

Redis Atomic Lua Script Inventory Reservation: Decrements available seats atomically in Redis memory before touching PostgreSQL:

local count = redis.call('GET', KEYS[1])
if tonumber(count) > 0 then
    redis.call('DECR', KEYS[1])
    return 1
else
    return 0
end

Optimistic Seat Locking in PostgreSQL:

UPDATE seats SET status = 'HELD', user_id = $1, lock_time = NOW()
WHERE id = $2 AND status = 'AVAILABLE';

3. Distributed Video Processing & Adaptive Streaming (YouTube / Netflix)

Ingestion & Chunking Raw video uploaded to S3 bucket triggers event to Kafka. Chunking worker splits video into 5-second GOP (Group of Pictures) chunks.

Transcoding Pipeline FFmpeg workers encode chunks into multiple resolutions (1080p, 720p, 480p) and codecs (H.264, AV1, VP9) in parallel.

HLS / DASH Delivery Generates master.m3u8 manifest playlist. Edge CDN caches video chunks close to users.

4. Real-time Location Tracking & Ride Matching (Uber / Lyft)

Geospatial Indexing (Google S2 / QuadTree / Geohash): Divides earth map into hierarchical 2D cell grids. Driver location updates (lat, long) emitted every 4 seconds over WebSocket are mapped to cell IDs stored in Redis.

Driver Match Radius Search: Querying nearby available drivers scans surrounding ring cells (\(O(1)\) lookup) within 2km radius without scanning global table rows.