nw-sd-case-studies

# 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) ### URL S...