What is the difference between AWS RDS and DynamoDB?

**RDS (Relational Database Service):**
- Managed SQL databases: MySQL, PostgreSQL, Oracle, SQL Server
- Structured data with fixed schema
- Supports complex joins and transactions
- Scales vertically (bigger instance)
- Best for: e-commerce orders, banking, traditional apps

**DynamoDB:**
- Managed NoSQL (key-value + document)
- Flexible schema — each row can have different attributes
- Scales horizontally — millions of requests per second
- Single-digit millisecond latency
- Best for: gaming leaderboards, user sessions, IoT data, real-time apps

**Choose RDS** when you need complex queries and relationships.
**Choose DynamoDB** when you need massive scale and simple lookups.