Lambda is tightly integrated with API Gateway. The ability to make synchronous calls from API Gateway to Lambda enables the creation of fully serverless applications and is described in detail in the Amazon API Gateway Developer Guide.

The following figure shows the architecture of a serverless microservice with AWS Lambda where the complete service is built out of managed services, which eliminates the architectural burden to design for scale and high availability, and eliminates the operational efforts of running and monitoring the microservice’s underlying infrastructure.

https://docs.aws.amazon.com/whitepapers/latest/microservices-on-aws/serverless-microservices.html