API Gateway synchrounously invokes a Lambda function, delivering an EVENT object that represents the web request.
The Lambda Function processes the event and uses the AWS SDK to connect to a DynamoDB table. The DynamoDB service responds to the Lambda function with the result of the operation.
The Lambda Function finishes processing and the result is sent back to API Gateway. API Gateway then responds back to the original client request.
The "client" can be a web browser, an application, or even another service in AWS.
Amazon API Gateway is a service that lets you route API requests. HTTP requeests are handled by API Gateway and invoke other services synchronously.
A Lambda Function receives events from the API Gateway route.
The DynamoDB service is a serverless, NoSQL database that can scale to thousands of transactions per second.