Spring Cloud Gateway

Spring Cloud Gateway aims to provide a simple, yet effective way to route to APIs and provide cross-cutting concerns to them such as security, monitoring/metrics, and resiliency.
https://spring.io/projects/spring-cloud-gateway

First, configure the project as a Eureka client as was explained here. Then, add this dependency:

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-gateway</artifactId>
</dependency>

If you add the next properties you can access other services registered in Eureka:

spring.cloud.gateway.discovery.locator.enabled=true
spring.cloud.gateway.discovery.locator.lowerCaseServiceId=true

The second property is optional and allows us to use lowercase to access the service. For instance, if you have a eureka client service named ACCOUNTS-MICROSERVICE, and the API Gateway project is running on port 8765 you can use this url: http://localhost:8765/accounts-microservice/accounts-microservice/accountDetails/1. Now, you are accessing the accounts-microservice service through the API gateway.

You can create a custom router for adding headers, parameters, and routing:

@Bean
public RouteLocator gatewayRouter(RouteLocatorBuilder builder) {
  return builder.routes()
      .route(p -> p.path("/accounts-microservice/**")
          .filters(f -> f
              .addRequestHeader("MyHeader", "MyURI")
              .addRequestParameter("Param", "MyValue"))
          .uri("lb://accounts-microservice"))
      .build();
}

Now, you can remove the two previous properties and use this simpler URL: http://localhost:8765/accounts-microservice/accountDetails/1. You can see the new header and parameter in the request. Besides, you can chain as many routes as you want in the same builder, add path rewrites, etc.

Additionally, Spring Cloud Gateway provides a GlobalFilter to handle cross-cutting concerns such as logging, lets see an example:

@Component
public class LoggingFilter implements GlobalFilter {

  private final Logger logger = LoggerFactory.getLogger(LoggingFilter.class);

  @Override
  public Mono<Void> filter(ServerWebExchange exchange,
      GatewayFilterChain chain) {
    logger.info("Path of the request received -> {}",
        exchange.getRequest().getPath());
    return chain.filter(exchange);
  }

}

For more information see: https://www.baeldung.com/spring-cloud-gateway