The What

API Gateways to extract bunch of code that would otherwise be inside your servers and extract it out to a different server.

The Why / Advantages

Authorization: User authentication can be done before sending the request to your microservices.

Transformation & Validation : Client would have the liberty to send data in a clean uniform format, API gateway would transform the data and validation then pass it to the microservice in a customized format.

Client can avoid DNS lookup: responsibility of routing to server and load balancing can be situated in API Gateway.

Rate limiting: API gateway can supervise the requests from the clients and prevent DDOS attacks.