Zookeeper系列(5)：使用Zookeeper作为注册中心

服务注册

引入相关依赖：

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.4.5</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>zkdemo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>zkdemo</name>
	<description>Demo project for Spring Boot</description>
	<properties>
		<java.version>1.8</java.version>
		<spring-cloud.version>2020.0.2</spring-cloud.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-zookeeper-discovery</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>

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

</project>

配置文件application.yml：

spring:
  cloud:
    zookeeper:
      # Zookeeper服务器地址，集群则以逗号分隔
      connect-string: localhost:2181
  application:
    name: zkdemo

# 使用随机端口
server:
  port: 0

主程序类ZkdemoApplication：

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

由于配置了使用随机端口，这里直接启动三个ZkdemoApplication运行三个zkdemo服务示例。

启动成功后，在zookeeper中查看节点的变化，会发现在根节点下多出来一个services节点，services节点下是以服务名称命名的服务节点，服务节点下是该服务的实例节点。

[zk: localhost:2181(CONNECTED) 96] ls -R / 
/
/services
/services/zkdemo
/services/zkdemo/2030bca0-db25-411d-b1f5-84c790bd1d6f
/services/zkdemo/208834cf-e7e4-496e-a5c0-afcbb78e120f
/services/zkdemo/2c4177e1-20fd-4c66-9ee0-eaf21253039d

实例节点中存储了服务名称、ip地址、端口号、实例ID等相关信息：

[zk: localhost:2181(CONNECTED) 97] get /services/zkdemo/208834cf-e7e4-496e-a5c0-afcbb78e120f 
{"name":"zkdemo","id":"208834cf-e7e4-496e-a5c0-afcbb78e120f","address":"localhost","port":64514,"sslPort":null,"payload":{"@class":"org.springframework.cloud.zookeeper.discovery.ZookeeperInstance","id":"zkdemo","name":"zkdemo","metadata":{"instance_status":"UP"}},"registrationTimeUTC":1619424602784,"serviceType":"DYNAMIC","uriSpec":{"parts":[{"value":"scheme","variable":true},{"value":"://","variable":false},{"value":"address","variable":true},{"value":":","variable":false},{"value":"port","variable":true}]}}

[zk: localhost:2181(CONNECTED) 98] get /services/zkdemo/2030bca0-db25-411d-b1f5-84c790bd1d6f
{"name":"zkdemo","id":"2030bca0-db25-411d-b1f5-84c790bd1d6f","address":"localhost","port":64401,"sslPort":null,"payload":{"@class":"org.springframework.cloud.zookeeper.discovery.ZookeeperInstance","id":"zkdemo","name":"zkdemo","metadata":{"instance_status":"UP"}},"registrationTimeUTC":1619424361059,"serviceType":"DYNAMIC","uriSpec":{"parts":[{"value":"scheme","variable":true},{"value":"://","variable":false},{"value":"address","variable":true},{"value":":","variable":false},{"value":"port","variable":true}]}}

[zk: localhost:2181(CONNECTED) 99] get /services/zkdemo/2c4177e1-20fd-4c66-9ee0-eaf21253039d
{"name":"zkdemo","id":"2c4177e1-20fd-4c66-9ee0-eaf21253039d","address":"localhost","port":64475,"sslPort":null,"payload":{"@class":"org.springframework.cloud.zookeeper.discovery.ZookeeperInstance","id":"zkdemo","name":"zkdemo","metadata":{"instance_status":"UP"}},"registrationTimeUTC":1619424510719,"serviceType":"DYNAMIC","uriSpec":{"parts":[{"value":"scheme","variable":true},{"value":"://","variable":false},{"value":"address","variable":true},{"value":":","variable":false},{"value":"port","variable":true}]}}

通过ephemeralOwner字段可以看出，services节点和服务节点为持久节点，实例节点为临时节点：

[zk: localhost:2181(CONNECTED) 100] stat /services 
cZxid = 0x118
ctime = Mon Apr 26 16:06:02 CST 2021
mZxid = 0x118
mtime = Mon Apr 26 16:06:02 CST 2021
pZxid = 0x119
cversion = 1
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 0
numChildren = 1

[zk: localhost:2181(CONNECTED) 101] stat /services/zkdemo 
cZxid = 0x119
ctime = Mon Apr 26 16:06:02 CST 2021
mZxid = 0x119
mtime = Mon Apr 26 16:06:02 CST 2021
pZxid = 0x11e
cversion = 3
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 0
numChildren = 3

[zk: localhost:2181(CONNECTED) 102] stat /services/zkdemo/2030bca0-db25-411d-b1f5-84c790bd1d6f 
cZxid = 0x11a
ctime = Mon Apr 26 16:06:02 CST 2021
mZxid = 0x11a
mtime = Mon Apr 26 16:06:02 CST 2021
pZxid = 0x11a
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x100000122cf000d
dataLength = 514
numChildren = 0

当某个实例出现故障停止时，对应的临时节点也会被删除。当服务节点下所有实例节点被删除时，服务节点也会被删除。当services节点下的所有服务节点被删除时，services节点也会被删除。

服务发现

通过DiscoveryClient从注册中心获取对应服务的实例列表：

@SpringBootTest
class ZkdemoApplicationTests {
	@Autowired
	private DiscoveryClient discoveryClient;

	@Test
	public void serviceUrl() {
		List<ServiceInstance> list = discoveryClient.getInstances("zkdemo");
		list.stream().forEach(obj -> System.out.println(obj.getUri().toString()));
	}
}

输出结果：

http://localhost:64401
http://localhost:64475
http://localhost:64514

服务调用这里就不演示了，可以使用Feign或RestTemplate进行调用。