Simple Spring Cloud Implementation

Tags:

Spring Cloud provides convenient tools for building cloud-native applications. A cloud-native system is designed for the cloud and commonly combines multiple small services into a larger system.

Architecture

This example implements service delivery with three applications:

  • DiscoveryServer: Registers application information and supports load balancing.
  • GatewayServer: Serves as the entry point for requests.
  • BackendService: Returns the actual response.

Implement DiscoveryServer

Use Netflix Eureka. Adding @EnableEurekaServer to a Spring Boot application is enough to create a Eureka server.

Create the Project

curl https://start.spring.io/starter.tgz  \
-d bootVersion=2.4.5 \
-d dependencies=spring-discovery-server \
-d baseDir=spring-eureka-server \
-d artifactId=discovery-server \
-d packageName=com.devkuma.cloud.discovery.server \
-d applicationName=DiscoveryServerApplication \
-d packaging=jar \
-d javaVersion=1.8 \
-d type=gradle-project | tar -xzvf -

Implement the Source Code

package com.devkuma.cloud.discovery.server;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

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

The server does not need to register itself or query the registry:

server:
  port: 8761
eureka:
  client:
    registerWithEureka: false
    fetchRegistry: false

Open http://localhost:8761/.

Spring cloud eureka

Create GatewayServer

GatewayServer communicates with clients and acts as a reverse proxy for BackendService.

Create the Project

curl https://start.spring.io/starter.tgz  \
-d bootVersion=2.4.5 \
-d dependencies=cloud-eureka,cloud-gateway \
-d baseDir=spring-gateway-server \
-d artifactId=gateway-server \
-d packageName=com.devkuma.cloud.gateway.server \
-d applicationName=GatewayServerApplication \
-d packaging=jar \
-d javaVersion=1.8 \
-d type=gradle-project | tar -xzvf -

Implement the Source Code

package com.devkuma.cloud.gateway.server;

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

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

server:
  port: 8001
spring:
  application:
    name: gateway-server
  cloud:
    gateway:
      routes:
        - id: backend-service
          uri: lb://backend-service
          predicates:
            - Path=/backend/**
          filters:
            - RewritePath=/backend/(?<path>.*),/$\{path}
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka
  instance:
    preferIpAddress: true

The application name is registered with Eureka. Requests to /backend/** are forwarded to BackendService.

Create BackendService

Create the Project

curl https://start.spring.io/starter.tgz  \
-d bootVersion=2.4.5 \
-d dependencies=cloud-eureka \
-d baseDir=spring-backend-service \
-d artifactId=backend-service \
-d packageName=com.devkuma.cloud.backend.service \
-d applicationName=BackendServiceApplication \
-d packaging=jar \
-d javaVersion=1.8 \
-d type=gradle-project | tar -xzvf -

Implement the Source Code

package com.devkuma.cloud.backend.service;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;

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

package com.devkuma.cloud.backend.service;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {
    @RequestMapping("/hello")
    public String hello() {
        return "Hello backend service";
    }
}

server:
  port: 8002
spring:
  application:
    name: backend-service
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka
  instance:
    preferIpAddress: true

Open http://localhost:8002/hello.

Spring cloud gateway backend

Finish

Start all applications and open http://localhost:8001/backend/hello.

Spring cloud backend

The complete project is available here.