Spring Cloud Kubernetes选主：为不同功能配置独立主节点

需求背景 #

已基于Spring Cloud Kubernetes实现单Pod执行定时任务的选主逻辑，现需扩展为Job1、Job2两个定时任务各自独立选主——不同Pod可分别作为两个任务的主节点，各自负责执行对应任务。

核心原理 #

Spring Cloud Kubernetes的Leader选举通过**独立的角色（Role）**区分不同选举组，每个角色对应一个Kubernetes ConfigMap作为锁资源。不同角色的选举完全隔离，只需为两个任务分配不同的选举角色，即可实现独立选主。

实现步骤 #

1. 保持Maven依赖不变 #

当前依赖已满足多角色选主需求，无需修改：

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>3.3.3</version>
    <relativePath/>
</parent>

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-kubernetes-fabric8-leader</artifactId>
</dependency>

2. 配置多角色选举规则 #

修改application.yaml，为两个任务分别配置独立的选举角色：

spring:
  cloud:
    kubernetes:
      leader:
        enabled: true
        autoStartup: true
        # 配置多个独立选举角色
        roles:
          - name: job1-leader
            namespace: ${spring.cloud.kubernetes.client.namespace:default}
          - name: job2-leader
            namespace: ${spring.cloud.kubernetes.client.namespace:default}

说明：每个角色的name需唯一，namespace可选，默认使用Pod所在的K8s命名空间。

3. 调整定时任务代码 #

每个任务仅响应自身角色的选举事件，修改ScheduledJob1和ScheduledJob2的事件监听逻辑：

ScheduledJob1（对应job1-leader角色）

import lombok.log4j.Log4j2;
import org.springframework.context.event.EventListener;
import org.springframework.integration.leader.event.OnGrantedEvent;
import org.springframework.integration.leader.event.OnRevokedEvent;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Log4j2
@Component
public class ScheduledJob1 {

    private boolean isJob1Leader = false;
    private static final String JOB1_ROLE = "job1-leader";

    @EventListener(OnGrantedEvent.class)
    public void onLeaderGranted(OnGrantedEvent event) {
        if (JOB1_ROLE.equals(event.getLeaderContext().getRole())) {
            log.info("Job1的主节点权限已授予当前实例");
            isJob1Leader = true;
        }
    }

    @EventListener(OnRevokedEvent.class)
    public void onLeaderRevoked(OnRevokedEvent event) {
        if (JOB1_ROLE.equals(event.getLeaderContext().getRole())) {
            log.info("Job1的主节点权限已从当前实例收回");
            isJob1Leader = false;
        }
    }

    @Scheduled(fixedRate = 2000)
    public void foo1() {
        if (isJob1Leader) {
            log.info("我是Job1的主节点，正在执行foo1任务");
        } else {
            log.info("当前不是Job1主节点，跳过foo1任务");
        }
    }
}

ScheduledJob2（对应job2-leader角色）

import lombok.log4j.Log4j2;
import org.springframework.context.event.EventListener;
import org.springframework.integration.leader.event.OnGrantedEvent;
import org.springframework.integration.leader.event.OnRevokedEvent;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Log4j2
@Component
public class ScheduledJob2 {

    private boolean isJob2Leader = false;
    private static final String JOB2_ROLE = "job2-leader";

    @EventListener(OnGrantedEvent.class)
    public void onLeaderGranted(OnGrantedEvent event) {
        if (JOB2_ROLE.equals(event.getLeaderContext().getRole())) {
            log.info("Job2的主节点权限已授予当前实例");
            isJob2Leader = true;
        }
    }

    @EventListener(OnRevokedEvent.class)
    public void onLeaderRevoked(OnRevokedEvent event) {
        if (JOB2_ROLE.equals(event.getLeaderContext().getRole())) {
            log.info("Job2的主节点权限已从当前实例收回");
            isJob2Leader = false;
        }
    }

    @Scheduled(fixedRate = 2000)
    public void foo2() {
        if (isJob2Leader) {
            log.info("我是Job2的主节点，正在执行foo2任务");
        } else {
            log.info("当前不是Job2主节点，跳过foo2任务");
        }
    }
}

4. 可选：Java代码自定义LeaderCandidate（更灵活） #

若需更精细控制选举逻辑，可通过Java配置类手动创建两个LeaderCandidate实例（与yaml配置二选一即可）：

import org.springframework.cloud.kubernetes.fabric8.leader.Fabric8LeaderCandidate;
import org.springframework.cloud.kubernetes.fabric8.leader.Fabric8LeaderProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class LeaderConfig {

    private static final String JOB1_ROLE = "job1-leader";
    private static final String JOB2_ROLE = "job2-leader";

    @Bean
    public Fabric8LeaderCandidate job1LeaderCandidate(Fabric8LeaderProperties properties) {
        return new Fabric8LeaderCandidate(properties, JOB1_ROLE);
    }

    @Bean
    public Fabric8LeaderCandidate job2LeaderCandidate(Fabric8LeaderProperties properties) {
        return new Fabric8LeaderCandidate(properties, JOB2_ROLE);
    }
}

验证要点 #

1. 部署至少2个Pod到K8s集群
2. 查看Pod日志，确认：
   • 其中一个Pod成为Job1的主节点，执行foo1任务
   • 另一个Pod成为Job2的主节点，执行foo2任务
   • 当某个Pod下线时，对应任务的主节点会自动切换到其他可用Pod

K8s权限说明 #

确保Pod拥有ConfigMap的读写权限，可通过RBAC配置：

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: default
  name: leader-role
rules:
  - apiGroups: [""]
    resources: ["configmaps"]
    verbs: ["get", "watch", "list", "create", "update", "delete"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  namespace: default
  name: leader-role-binding
subjects:
  - kind: ServiceAccount
    name: default
roleRef:
  kind: Role
  name: leader-role
  apiGroup: rbac.authorization.k8s.io

内容的提问来源于stack exchange，提问作者Georgii Lvov