Spring cloud eureka feign

1. Introduction Service discovery is a very core function
in the microservice architecture. The Netflix Service Discovery component eureka can be easily integrated in spring cloud. Eureka includes server and client. The server side can be provided in the form of a cluster, and each server can achieve high availability by synchronizing the service status registered in other servers.
When an Eureka client registers with the server, it will provide its own metadata information, including host, port, health check URI and other information. The Eureka server determines whether the current instance is normal by listening to the heartbeat information of different instances of the same service. If the heartbeat information fails, the instance will be automatically removed.

To call services registered in Eureka, instead of using EurekaClient directly, you can use declarative rest client :feign, or Spring RestTemplate to more conveniently call services registered in Eureka.

2. Examples

1. Eureka server

The core is to add the spring-cloud-starter-eureka-server dependency to the normal Spring boot program, and add the @EnableEurekaServer annotation to the startup class

Code structure:

startup class

package hello;

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

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

pom file

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.example</groupId>
	<artifactId>eureka-service</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>1.5.1.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-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>Camden.SR5</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

	<repositories>
		<repository>
			<id>spring-snapshots</id>
			<name>Spring Snapshots</name>
			<url>https://repo.spring.io/libs-snapshot</url>
			<snapshots>
				<enabled>true</enabled>
			</snapshots>
		</repository>
	</repositories>

</project>

Application configuration information

server.port=8761

eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false

logging.level.com.netflix.eureka=OFF
logging.level.com.netflix.discovery=OFF

2. Eureka client (ie user server side)

The core is to add the spring-cloud-starter-eureka dependency to the normal Spring boot program, and add the @EnableDiscoveryClient annotation to the startup class

Code structure:

startup class

package demo;

import java.util.Arrays;
import java.util.List;
import java.util.Random;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author Spencer Gibb
 */
@SpringBootApplication
@EnableDiscoveryClient
@RestController
public class HelloServerApplication {

	@RequestMapping("/greeting")
	public String hello() {
		List<String> greeting = Arrays.asList("Hi there","Greetings","Salutations");
		Random rand = new Random();
		int randomNum = rand.nextInt(greeting.size());
		return greeting.get(randomNum);
	}

	public static void main(String[] args) {
		SpringApplication.run(HelloServerApplication.class, args);
	}
}

pom file

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>org.test</groupId>
	<artifactId>feign-eureka-hello-server</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>feign-eureka-hello-server</name>
	<description>Demo project for Spring Cloud</description>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>1.5.1.RELEASE</version>
		<relativePath /> <!-- lookup parent from repository -->
	</parent>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<java.version>1.8</java.version>
	</properties>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.springframework.cloud</groupId>
				<artifactId>spring-cloud-dependencies</artifactId>
				<version>Camden.SR5</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-actuator</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-feign</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-eureka</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

Application configuration information

spring:
  application:
    name: HelloServer

server:
  port: 7111

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
  instance:
    leaseRenewalIntervalInSeconds: 10
    metadataMap:
      instanceId: ${vcap.application.instance_id:${spring.application.name}:${spring.application.instance_id:${server.port}}}

3. User client (calls the Eureka client registered in the Eureka server)

The core is to add spring-cloud-starter-eureka and spring-cloud-starter-feign dependencies to the normal Spring boot program, and add the @EnableFeignClients annotation to the startup class

Code structure:

startup class

package demo;

import static org.springframework.web.bind.annotation.RequestMethod.GET;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author Spencer Gibb
 */
@SpringBootApplication
@RestController
@EnableFeignClients
public class HelloClientApplication {
	@Autowired
	HelloClient client;

	@RequestMapping("/greeting")
	public String hello() {
		return client.hello();
	}

	public static void main(String[] args) {
		SpringApplication.run(HelloClientApplication.class, args);
	}

	@FeignClient("HelloServer")
	interface HelloClient {
		@RequestMapping(value = "/greeting", method = GET)
		String hello();
	}
}

The service id in FeignClient should be consistent with the value of spring.application.name in the User server configuration information

pom file

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>org.test</groupId>
	<artifactId>feign-eureka-hello-client</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>feign-eureka-hello-client</name>
	<description>Demo project for Spring Cloud</description>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>1.5.1.RELEASE</version>
		<relativePath /> <!-- lookup parent from repository -->
	</parent>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<java.version>1.8</java.version>
	</properties>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.springframework.cloud</groupId>
				<artifactId>spring-cloud-dependencies</artifactId>
				<version>Camden.SR5</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-actuator</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-feign</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-eureka</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

Application configuration information

spring:
  application:
    name: HelloClient

server:
  port: 7211

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
  instance:
    leaseRenewalIntervalInSeconds: 10
    metadataMap:
      instanceId: ${vcap.application.instance_id:${spring.application.name}:${spring.application.instance_id:${server.port}}}


endpoints:
  restart:
    enabled: true
  shutdown:
    enabled: true
  health:
    sensitive: false

3.
Start Start the
Eureka server -> user server -> user client
and other applications in the following order. After all applications are started, visit http://localhost:7211/greeting through the interface, and you can access the return value of the method in the user-server normally. The process is to access the hello method in the user client project through the interface. The user client obtains the registered HelloServer instance from the Eureka server through the service id specified in @FeignClient, that is, the user server, and then calls the hello method in the user server, and returns the call result to user client, and finally return to the interface

4. Eureka cluster

1. Modify the configuration file corresponding to Eureka-server

spring:
  application:
    name: eureka-server-clustered
  profiles: primary
server:
  port: 8011
eureka:
  instance:
    hostname: eureka-primary
  client:
    registerWithEureka: false
    fetchRegistry: false
    serviceUrl:
      defaultZone: http://eureka-secondary:8012/eureka/,http://eureka-tertiary:8013/eureka/

---
spring:
  application:
    name: eureka-server-clustered
  profiles: secondary
server:
  port: 8012
eureka:
  instance:
    hostname: eureka-secondary
  client:
    registerWithEureka: false
    fetchRegistry: false
    serviceUrl:
      defaultZone: http://eureka-tertiary:8013/eureka/,http://eureka-primary:8011/eureka/

---
spring:
  application:
    name: eureka-server-clustered
  profiles: tertiary
server:
  port: 8013
eureka:
  instance:
    hostname: eureka-tertiary
  client:
    registerWithEureka: false
    fetchRegistry: false
    serviceUrl:
      defaultZone: http://eureka-primary:8011/eureka/,http://eureka-secondary:8012/eureka/

2. Modify the configuration file corresponding to the user-server

spring:
  application:
    name: UserServer

server:
  port: 7111

eureka:
  client:
    serviceUrl:
      defaultZone: http://eureka-secondary:8012/eureka/
  instance:
    leaseRenewalIntervalInSeconds: 10
    metadataMap:
      instanceId: ${vcap.application.instance_id:${spring.application.name}:${spring.application.instance_id:${server.port}}}

Note: application.name has been modified, and the serviceid corresponding to feignclient also needs to be modified

3. Modify the configuration file corresponding to user-client

spring:
  application:
    name: UserClient

server:
  port: 7211

eureka:
  client:
    serviceUrl:
      defaultZone: http://eureka-primary:8011/eureka/,http://eureka-secondary:8012/eureka/,http://eureka-tertiary:8013/eureka/
  instance:
    leaseRenewalIntervalInSeconds: 10
    metadataMap:
      instanceId: ${vcap.application.instance_id:${spring.application.name}:${spring.application.instance_id:${server.port}}}


endpoints:
  restart:
    enabled: true
  shutdown:
    enabled: true
  health:
    sensitive: false

3. If on the same machine, modify the hosts

#	127.0.0.1       localhost
#	::1	localhost
127.0.0.1       localhost
127.0.0.1       eureka-primary
127.0.0.1       eureka-secondary
127.0.0.1       eureka-tertiary

Start Eureka-server user-server user-client in turn, where Eureka-server is started with

java -jar eureka-server-clustered-0.0.1-SNAPSHOT.jar --spring.profiles.active=primary
java -jar eureka-server-clustered-0.0.1-SNAPSHOT.jar --spring.profiles.active=secondary
java -jar eureka-server-clustered-0.0.1-SNAPSHOT.jar --spring.profiles.active=tertiary

Start three times, at this time Eureka-server provides services in the form of a cluster, you can close any one or two to test the high availability of Eureka

primary

secondary

tertiary

Spring cloud eureka feign

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