Patterns that appear across every Amazon system design question:
Microservices over monolith. Amazon runs thousands of independent services.
Event-driven architecture. SQS and SNS decouple services and absorb traffic spikes.
Caching layer. ElastiCache (Redis) for hot data. Cache-aside pattern.
Database selection. DynamoDB for flexible, read-heavy data. RDS for transactions. S3 for files.
Load balancing. Application Load Balancer distributes traffic across instances.
Idempotency. Every write operation should be safe to retry without side effects.
When in doubt, split your design into independent services connected by message queues.