springcloud openfeign 偶现 Caused by: java.net.UnknownHostException

背景

最近查看日志发现某服务偶现Caused by: java.net.UnknownHostException
同时查看eureka的access.log 出现如下异常

10.xxx.xxx.xxx - - [27/May/2025:23:57:29 +0800] “PUT /eureka/apps/{appName}/{host}:xxx-job:8082?status=UP&lastDirtyTimestamp=1748351637173 HTTP/1.1” 404 -

问题关联分析

1. 问题链条

Eureka心跳续约失败(404) → 服务从注册中心下线 → 服务发现失败 → DNS解析失败 → UnknownHostException

2. 具体流程

1. xxx-job 服务向Eureka发送心跳续约请求
2. Eureka Server返回404，表示该服务实例不存在
3. 经过几次失败后，Eureka Server将该服务实例从注册表中移除
4. 其他服务调用 xxx-job 时，从Eureka获取不到该服务的实例信息
5. Spring Cloud LoadBalancer无法解析 xxx-job 服务名
6. 最终抛出 UnknownHostException: xxx-job

为什么会出现404错误

1. 服务注册不完整

# 可能的配置问题
eureka:client:initial-instance-info-replication-interval-seconds: 40  # 初始注册延迟太长instance-info-replication-interval-seconds: 30

2. Eureka Server清理策略

# Eureka Server可能过于激进地清理实例
eureka:server:eviction-interval-timer-in-ms: 60000  # 清理间隔enable-self-preservation: false       # 自我保护模式关闭

3. 网络问题导致注册失败

实例ID中的 host 可能存在DNS解析问题。

解决方案

1. 修复服务注册配置

eureka:client:service-url:defaultZone: http://eureka-server:8761/eureka/register-with-eureka: truefetch-registry: trueinitial-instance-info-replication-interval-seconds: 5instance-info-replication-interval-seconds: 10instance:prefer-ip-address: trueip-address: xxx.xxx.xxx.xxxinstance-id: ${spring.application.name}:${spring.cloud.client.ip-address}:${server.port}lease-renewal-interval-in-seconds: 10lease-expiration-duration-in-seconds: 30

2. 启用Eureka Server自我保护模式

eureka:server:enable-self-preservation: truerenewal-percent-threshold: 0.85eviction-interval-timer-in-ms: 120000

3. 添加重试机制

# 为Feign客户端添加重试
feign:client:config:default:retryer: feign.Retryer.Default

4. 监控和诊断

@Component
public class ServiceHealthMonitor {@Autowiredprivate EurekaClient eurekaClient;@Scheduled(fixedRate = 30000)public void checkServiceHealth() {Application app = eurekaClient.getApplication("xxx-job");if (app == null || app.getInstances().isEmpty()) {logger.warn("xxx-job服务不可用");}}
}

5. 应急预案

@Component
public class ServiceFallback {@Retryable(value = UnknownHostException.class, maxAttempts = 3)public String callXxxjob() {// 服务调用逻辑}@Recoverpublic String recover(UnknownHostException ex) {logger.error("服务调用失败，启用降级策略", ex);return "服务暂时不可用";}
}

验证步骤

1. 检查Eureka Dashboard：确认xxx-job服务是否持续在线
2. 监控日志：观察404错误的频率和时间模式
3. 测试网络：ping host
4. 检查服务启动顺序：确保Eureka Server先启动

这个问题的核心是服务注册中心的状态不一致，建议重点解决服务注册稳定性问题。