An API Gateway acts as a single entry point for all client requests to your application's backend services. Instead of sending requests directly to each service, clients send their requests to the API Gateway. The gateway then routes each request to the correct service, collects the results, and returns a single response to the client. This approach simplifies client interactions, improves security, and allows you to manage tasks like authentication, logging, and rate limiting in one place.

How an API Gateway Handles Requests

An API Gateway acts as a front door for all your application's services. When a client, such as a web browser or mobile app, wants to access your system, it sends requests to the API Gateway instead of directly contacting each service.

Request Flow Through the API Gateway

1. Receives client requests;
   When you make a request, like GET /orders/123, the API Gateway receives it first.
2. Routes requests to the correct service;
   The gateway examines the request path and decides which service should handle it. For example, requests starting with /orders go to the Order Service, while /users go to the User Service.
3. Applies security checks;
   Before forwarding your request, the gateway checks if you are allowed to access the resource. This might include verifying your login token or checking your permissions.
4. Forwards the request and collects the response;
   If you pass the security checks, the gateway sends your request to the correct service. The service processes the request and sends a response back to the gateway.
5. Returns the response to the client.
   The gateway takes the response from the service and sends it back to you, the client.

Example Scenario

Suppose you use a shopping app to view your order history. Your app sends a request to the API Gateway at GET /orders/history:

• The API Gateway receives the request and checks your login token.
• It sees the request is for order history, so it routes the request to the Order Service.
• The Order Service returns the list of orders.
• The API Gateway sends this list back to your app.

This process keeps your services secure and organized, while making it easy for clients to interact with your application through a single entry point.