The main differences between Amazon RDS and DynamoDB are:
1. RDS provides fully managed relational databases like MySQL, PostgreSQL, and Oracle that support SQL queries, transactions, complex joins, and foreign keys. DynamoDB is a fully managed NoSQL database that supports fast lookups and scaling via key-value and document data models without complex relations.
2. RDS is best suited for applications that require ACID transactions, relational structures, and complex read-write queries. DynamoDB fits better with highly scaled apps needing fast, simple data access.
3. RDS offers more robust backup, recovery, and disaster recovery capabilities as a relational database service. DynamoDB focuses more on performance and scalability as a distributed NoSQL database.
4. RDS gives you full control over the relational schema and indexes. DynamoDB manages the underlying infrastructure and uses flexible data models with optional indexes.
RDS simplifies running relational databases in the cloud while DynamoDB provides a non-relational database optimized for speed, flexibility, and scalability of modern applications. The choice depends on the data model, transactions, and querying needs.