In this article, we will integrate spring cloud gateway with a microservice-based architecture application using spring cloud. In the process, we will use spring cloud gateway as a gateway provider, Netflix Eureka as a discovery server, with circuit breaker pattern using Netflix Hystrix.

Let's quickly get started with the implementation of it.

Discovery Server Implementation

In a microservice architecture, service discovery is one of the key tenets. Service discovery automates the process of multiple instance creations on demand and provides high availability of our microservices.

Below are the pom.xml and application.yml configuration for integrating Netflix Eureka Discovery with Spring Cloud.

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

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>

<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<repositories>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
</repository>
</repositories>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>

application.yml

spring:
  application:
    name: discovery-service

eureka:
  client:
    eureka-server-connect-timeout-seconds: 5
    enabled: true
    fetch-registry: false
    register-with-eureka: false

server:
  port: 8761

Project Setup

First, we will generate a sample spring boot project from https://start.spring.io and import into the workspace. The selected dependencies are Gateway, Hystrix, and Actuator.

We will also add spring-cloud-starter-netflix-eureka-client dependency in our pom.

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

Spring Cloud Route Configuration

The route is the basic building block of the gateway. It is defined by an ID, a destination URI, a collection of predicates and a collection of filters. A route is matched if an aggregate predicate is true.

Spring Cloud Gateway provides many built-in Route Predicate Factories such as Path, Host, Date/Time, Method, Header, etc. We can use these built-in routes with conjunction with and() or () to define our routes. Once a request reaches to the gateway, the first thing gateway does is to match the request with each of the available route based on the predicate defined and the request is routed to the matched route.

Below is our route configuration. We have 2 different routes defined for our 2 microservices — first-service and second-service.

BeanConfig.java

package com.devglan.gatewayservice;

import org.springframework.cloud.gateway.route.RouteLocator;
import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class BeanConfig {

    @Bean
    public RouteLocator gatewayRoutes(RouteLocatorBuilder builder) {
        return builder.routes()
                .route(r -> r.path("/api/v1/first/**")
                        .filters(f -> f.rewritePath("/api/v1/first/(?.*)", "/${remains}")
                                .addRequestHeader("X-first-Header", "first-service-header")
                                .hystrix(c -> c.setName("hystrix")
                                        .setFallbackUri("forward:/fallback/first")))
                        .uri("lb://FIRST-SERVICE/")
                        .id("first-service"))

                .route(r -> r.path("/api/v1/second/**")
                        .filters(f -> f.rewritePath("/api/v1/second/(?.*)", "/${remains}")
                                .hystrix(c -> c.setName("hystrix")
                                        .setFallbackUri("forward:/fallback/second")))
                        .uri("lb://SECOND-SERVICE/")
                        .id("second-service"))
                .build();
    }

}

Spring Cloud Gateway Application Config

hystrix.command.fallbackcmd.execution.isolation.thread.timeoutInMilliseconds: 2000
spring:
  application:
    name: api-gateway

server:
  port: 8088

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka
    register-with-eureka: false
  instance:
    preferIpAddress: true

management:
  endpoints:
    web:
      exposure:
        include: hystrix.stream

Microservices Implementation

First Service

These services are a very simple implementation with only one controller defined for demo purpose.

FirstController.java

package com.devglan.gatewayservice.controller;

import org.springframework.web.bind.annotation.*;

@RestController
public class FirstController {

    @GetMapping("/test")
    public String test(@RequestHeader("X-first-Header") String headerValue){
        return headerValue;
    }

}

application.yaml

spring:
  application:
    name: first-service
server:
  port: 8086

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka

Second Service Implementation

@RestController
public class SecondController {

    @GetMapping("/second")
    public String test(@RequestHeader("X-second-Header") String headerValue){
        return headerValue;
    }

}

application.yaml

spring:
  application:
    name: second-service
server:
  port: 8087

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka

Now, as per the route configuration, the request matching the regex /api/v1/first/** will be forwarded to first-service whereas the request matching the regex /api/v1/second/** will be forwarded to second-service.

Conclusion

This concludes an example of using Spring Cloud Gateway to route requests to multiple services running downstream. Next, we can extend this example to integrate security at the gateway level.