Old School (2015-2020): Memorize 15 common designs (URL shortener, Twitter, Uber). Draw boxes. Calculate QPS. Done.
| Problem | Classic Solution | Modern Twist (2025) | |--------|----------------|---------------------| | | Read replicas, caching | Distributed SQL (Spanner, CockroachDB) + Varnish at edge | | High write throughput | Queue (Kafka) + batch writes | Tiered storage: hot (Redis), warm (Postgres), cold (S3) | | Global low latency | CDN for static, anycast routing | Edge computing (Cloudflare Workers, Lambda@Edge) | | Consistency vs. availability | Leader-follower replication | CRDTs (for collaborative editing) or Paxos/Raft | | Search inside data | Elasticsearch index | Zero-ETL from primary DB to search index | | Real-time updates | WebSocket servers | Server-sent events (SSE) + Redis pub/sub |
Pick your weapons from this table: