This microservices is use AWS Lambda function for computing.

This Order Acknowledgment Microservice does 4 thing;

1- first it verifies the request and generates the order Id

2- insert item order data into dynamodb table

3- Lambda sends a confirmation message back to api gateway with order Id

And lastly, this microservices publish a message to Amazon SNS which will be send downstream to different microservices. This message will be pub/sub messaging using SNS and this Order Acknowledgment Microservice will be the publisher of message.

https://medium.com/aws-lambda-serverless-developer-guide-with-hands/publish-subscribe-fan-out-pattern-in-serverless-architectures-using-sns-sqs-and-lambda-bccaa3abac9e