Routes are the rules that tell your API Gateway where to send incoming requests. When a client tries to reach a specific service, the API Gateway uses these routes to decide which backend service should handle the request.

Defining routes is important because it lets you control how requests move through your system. With clear routes, you can organize your APIs, hide internal details, and make it easier to manage multiple services in one place. This keeps your system secure, efficient, and easy to update as your application grows.

How Routes Are Defined in Spring Boot with Spring Cloud Gateway

In Spring Boot, you use Spring Cloud Gateway to manage how requests are routed to different services. A route is a rule that tells the gateway how to handle incoming HTTP requests based on their path or other details.

Basic Route Structure

A route usually has two main parts:

• A predicate: this checks if a request matches certain conditions, such as a URL path;
• A destination URI: this is where matching requests are sent.

You define routes in your application.yml file or with Java code. The most common way for beginners is using the application.yml file.

Example: Path Matching and Forwarding

Suppose you want to forward all requests from /users/** to a user service running at http://localhost:8081. Here is how you define this route:

spring:
  cloud:
    gateway:
      routes:
        - id: user-service
          uri: http://localhost:8081
          predicates:
            - Path=/users/**

• The id is a unique name for the route;
• The uri is the address where the request is forwarded;
• The Path=/users/** means any request starting with /users/ will match this route.

How Path Matching Works

The Path predicate uses patterns to match URLs. The double asterisk (**) matches any path after /users/, such as /users/123 or /users/profile/edit.

Forwarding Requests

When a request comes to the gateway at /users/123, the gateway checks the routes. If the path matches /users/**, the gateway forwards the request to http://localhost:8081/users/123.

This setup lets you control how incoming requests are routed to different backend services, making your application more organized and scalable.