Eureka Server的心跳续约就是客户端每隔一段时间向注册中心发送一次心跳，以证明自己没有发生故障。
    下面看下server端的代码

    1. @PUT
    2.     public Response renewLease(
    3.             @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication,
    4.             @QueryParam("overriddenstatus") String overriddenStatus,
    5.             @QueryParam("status") String status,
    6.             @QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) {
    7.         // 是否是服务端的同步请求
    8.         boolean isFromReplicaNode = "true".equals(isReplication);
    9.         // 心跳续约
    10.         boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);
    12.         // Not found in the registry, immediately ask for a register
    13.         if (!isSuccess) {
    14.             logger.warn("Not Found (Renew): {} - {}", app.getName(), id);
    15.             // 没有续约成功则发回一个NOT_FOUND状态码给客户端
    16.             return Response.status(Status.NOT_FOUND).build();
    17.         }
    18.         // Check if we need to sync based on dirty time stamp, the client
    19.         // instance might have changed some value
    20.         Response response = null;
    21.         if (lastDirtyTimestamp != null && serverConfig.shouldSyncWhenTimestampDiffers()) {
    22.             response = this.validateDirtyTimestamp(Long.valueOf(lastDirtyTimestamp), isFromReplicaNode);
    23.             // Store the overridden status since the validation found out the node that replicates wins
    24.             if (response.getStatus() == Response.Status.NOT_FOUND.getStatusCode()
    25.                     && (overriddenStatus != null)
    26.                     && !(InstanceStatus.UNKNOWN.name().equals(overriddenStatus))
    27.                     && isFromReplicaNode) {
    28.                 registry.storeOverriddenStatusIfRequired(app.getAppName(), id, InstanceStatus.valueOf(overriddenStatus));
    29.             }
    30.         } else {
    31.             response = Response.ok().build();
    32.         }
    33.         logger.debug("Found (Renew): {} - {}; reply status={}", app.getName(), id, response.getStatus());
    34.         return response;
    35.     }

    当客户端发送心跳连接时将会调用InstanceResource类的renewLease方法

    1. public boolean renew(final String appName, final String id, final boolean isReplication) {
    2.      if (super.renew(appName, id, isReplication)) {
    3.          // 续约成功，则同步集群
    4.          replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);
    5.          return true;
    6.      }
    7.      return false;
    8. }
    1. public boolean renew(String appName, String id, boolean isReplication) {
    2.         RENEW.increment(isReplication);
    3.         // 通过微服务名称拿到服务组
    4.         Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
    5.         Lease<InstanceInfo> leaseToRenew = null;
    6.         if (gMap != null) {
    7.             // 根据服务实例id拿到对应的服务实例
    8.             leaseToRenew = gMap.get(id);
    9.         }
    10.         if (leaseToRenew == null) {
    11.             RENEW_NOT_FOUND.increment(isReplication);
    12.             logger.warn("DS: Registry: lease doesn't exist, registering resource: {} - {}", appName, id);
    13.             return false;
    14.         } else {
    15.             InstanceInfo instanceInfo = leaseToRenew.getHolder();
    16.             if (instanceInfo != null) {
    17.                 // touchASGCache(instanceInfo.getASGName());
    18.                 InstanceStatus overriddenInstanceStatus = this.getOverriddenInstanceStatus(
    19.                         instanceInfo, leaseToRenew, isReplication);
    20.                 if (overriddenInstanceStatus == InstanceStatus.UNKNOWN) {
    21.                     logger.info("Instance status UNKNOWN possibly due to deleted override for instance {}"
    22.                             + "; re-register required", instanceInfo.getId());
    23.                     RENEW_NOT_FOUND.increment(isReplication);
    24.                     return false;
    25.                 }
    26.                 if (!instanceInfo.getStatus().equals(overriddenInstanceStatus)) {
    27.                     logger.info(
    28.                             "The instance status {} is different from overridden instance status {} for instance {}. "
    29.                                     + "Hence setting the status to overridden status", instanceInfo.getStatus().name(),
    30.                                     instanceInfo.getOverriddenStatus().name(),
    31.                                     instanceInfo.getId());
    32.                     instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus);
    34.                 }
    35.             }
    36.             renewsLastMin.increment();
    37.             // 心跳续约
    38.             leaseToRenew.renew();
    39.             return true;
    40.         }
    41.     }
    1. public void renew() {
    2.         // duration 默认为90秒，这个可以在配置文件中配置
    3.         // 将最后操作时间更新为当前时间+心跳续约时长
    4.         lastUpdateTimestamp = System.currentTimeMillis() + duration;
    5.     }

    主要步骤：

    • 客户端发送一个心跳续约请求，通过客户端传来的微服务名称和实例id拿到相应的实例对象，
    • 将这个服务的最后操作时间赋值为当前系统时间加上心跳续约时长
    • 同步各个注册集群中的续约时间