System Design Case Studies

Reference catalog of 25 real-world designs. Use when designing a similar system or needing precedent for architectural decisions.

Volume 1 Case Studies

Rate Limiter

Scale: API gateway middleware | Core: Token Bucket (industry standard) or Sliding Window Counter | Storage: Redis counters with TTL | Distributed: Lua scripts for atomic increment | Key insight: cross-cutting concern, belongs in middleware/gateway | Headers: 429 + Retry-After + X-RateLimit-Remaining

Consistent Hashing

Core: hash ring 0 to 2^32-1, servers at positions, keys walk clockwise | Virtual nodes: 100-200 per server, reduces load deviation from ~40% to ~5% | Used in: DynamoDB, Cassandra, Akamai, Discord | Key insight: never deploy without virtual nodes

Key-Value Store (Dynamo-style)

Core: consistent hashing for partitioning, N replicas on clockwise nodes, quorum W+R>N | Conflict: vector clocks, LWW, app-level merge | Failures: sloppy quorum + hinted handoff (temp), Merkle trees + anti-entropy (permanent), gossip for detection | Write path: WAL -> memtable -> SSTable (LSM-tree) | Read path: memtable -> Bloom filter -> SSTable(s)

Unique ID Generator

Winner: Snowflake -- 64-bit, sortable, minimal coordination | [1 unused | 41 timestamp | 5 DC | 5 machine | 12 sequence] ~4M IDs/sec/DC | Weakness: clock sync (NTP) | Alt: UUID (128-bit, not sortable), ticket server (SPOF)