Spring Cloud - Gateway

Introduction

In a distributed environment, services need to communicate with each other. However, this is interservice communication. We also have use-cases where a client outside our domain wants to hit our services for the API. So, either we can expose the address of all our microservices which can be called by clients OR we can create a Service Gateway which routes the request to various microservices and responds to the clients.

Creating a Gateway is much better approach here. There are two major advantages −

• The security for each individual services does not need to maintained.

• And, cross-cutting concerns, for example, addition of meta-information can be handled at a single place.

Netflix Zuul and Spring Cloud Gateway are two well-known Cloud Gateways which are used to handle such situations. In this tutorial, we will use Spring Cloud Gateway.

Spring Cloud Gateway Dependency Setting

Let us use the case of Restaurant which we have been using. Let us add a new service (gateway) in front of our two services, i.e., Restaurant services and Customer Service. First, let us update the pom.xml of the service with the following dependency −

<dependencies>
   <dependency>
         <groupId>org.springframework.cloud</groupId>
         <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
   </dependency>
   <dependency>
         <groupId>org.springframework.cloud</groupId>
         <artifactId>spring-cloud-starter-gateway</artifactId>
   </dependency>
</dependencies>

And then, annotate our Spring application class with the correct annotation, i.e., @EnableDiscoveryClient.

package com.tutorialspoint;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

@SpringBootApplication
@EnableDiscoveryClient
public class RestaurantGatewayService{
   public static void main(String[] args) {
      SpringApplication.run(RestaurantGatewayService.class, args);
   }
}

We are annotating with @EnableDiscoveryClient because we want to use Eureka service discovery to get the list of hosts which are serving a particular use-case

Dynamic Routing with Gateway

The Spring Cloud Gateway has three important parts to it. Those are −

• Route − These are the building blocks of the gateway which contain URL to which request is to be forwarded to and the predicates and filters that are applied on the incoming requests.

• Predicate − These are the set of criteria which should match for the incoming requests to be forwarded to internal microservices. For example, a path predicate will forward the request only if the incoming URL contains that path.

• Filters − These act as the place where you can modify the incoming requests before sending the requests to the internal microservices or before responding back to the client.