System design templates

Nine reference architectures you can run, break and fix — each with a scripted fault and a lesson to look for.

One small server and an embedded database. Traffic ramps up until the single machine runs out of memory.

Nginx in front of two app servers and one PostgreSQL. The app tier scales; the database becomes the bottleneck.

ALB → three EC2 servers using ElastiCache (cache-aside) in front of RDS PostgreSQL. At 60 s Redis is flushed.

CloudFront → ALB → an auto-scaling group → Aurora with two read replicas. At 40 s the primary fails.

API Gateway → Lambda → SQS → workers → DynamoDB. A traffic spike hits at 20 s.

ALB → EKS → Kafka (MSK, 6 partitions, 60 s retention) → consumers → PostgreSQL and OpenSearch.

Vercel functions → Neon Postgres, with Upstash Redis as a cache. Every function invocation can open a database connection.

Route 53 → two zones, each with an ALB and EKS → Aurora writer in zone A with a replica in zone B. Zone A fails at 40 s.

API servers → Redis → Cassandra. A celebrity post makes one key take 60% of the traffic.