本文详细解析了Eureka Server的启动流程，包括配置加载、服务接口策略（如Jersey框架）、服务注册与续约接口，以及Eureka Client的注册、下架和心跳续约操作。深入剖析了实例注册、同步与复制机制。
文章目录
Eureka Server启动过程
⼊⼝：SpringCloud充分利⽤了SpringBoot的⾃动装配的特点
-
观察eureka-server的jar包，发现在META-INF下⾯有配置⽂件spring.factories
springboot应⽤启动时会加载EurekaServerAutoConfiguration⾃动配置类 -
EurekaServerAutoConfiguration类
⾸先观察类头分析
-
** 需要有⼀个marker bean**，才能装配Eureka Server，那么这个marker其实是由
@EnableEurekaServer注解决定的
也就是说只有添加了@EnableEurekaServer注解，才会有后续的动作，这是成为⼀个EurekaServer的前提 -
关注EurekaServerAutoConfiguration
⽽在 com.netflix.eureka.cluster.PeerEurekaNodes#start⽅法中
回到主配置类中
回到主配置类中
- 关注EurekaServerInitializerConfiguration
重点关注，进⼊
org.springframework.cloud.netflix.eureka.server.EurekaServerBootstrap#contextInitialized
重点关注initEurekaServerContext()
研究⼀下上图中的syncUp⽅法
com.netflix.eureka.registry.PeerAwareInstanceRegistryImpl#syncUp
继续研究com.netflix.eureka.registry.AbstractInstanceRegistry#register（提供实例注册功能）
回到 org.springframework.cloud.netflix.eureka.server.EurekaServerBootstrap#initEurekaServerContext方法中
继续研究com.netflix.eureka.registry.PeerAwareInstanceRegistryImpl#openForTraffic
进⼊postInit()⽅法查看
Eureka Server服务接口暴露策略
在Eureka Server启动过程中主配置类注册了Jersey框架（是⼀个发布restful⻛格接⼝的框架，类似于我们的springmvc）
注⼊的Jersey细节
扫描classpath下的那些packages呢？已经定义好了
对外提供的接⼝服务，在Jersey中叫做资源
这些就是使⽤Jersey发布的供Eureka Client调⽤的Restful⻛格服务接⼝（完成服务注册、⼼跳续约等接⼝）
Eureka Server服务注册接⼝（接受客户端注册服务）
ApplicationResource类的addInstance()⽅法中代码：registry.register(info,“true”.equals(isReplication));
com.netflix.eureka.registry.PeerAwareInstanceRegistryImpl#register - 注册服务信息并同步到其它Eureka节点
AbstractInstanceRegistry#register()：注册，实例信息存储到注册表是⼀个ConcurrentHashMap
/**
* Registers a new instance with a given duration.
*
* @see com.netflix.eureka.lease.LeaseManager#register(java.lang.Object, int, boolean)
*/
public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
read.lock();//读锁
try {
// registry是保存所有应⽤实例信息的Map：ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>
// 从registry中获取当前appName的所有实例信息
Map<String, Lease<InstanceInfo>> gMap = registry.get(registrant.getAppName());
REGISTER.increment(isReplication);//注册统计+1
// 如果当前appName实例信息为空，新建Map
if (gMap == null) {
final ConcurrentHashMap<String, Lease<InstanceInfo>> gNewMap = new ConcurrentHashMap<String, Lease<InstanceInfo>>();
gMap = registry.putIfAbsent(registrant.getAppName(), gNewMap);
if (gMap == null) {
gMap = gNewMap;
}
}
// 获取实例的Lease租约信息
Lease<InstanceInfo> existingLease = gMap.get(registrant.getId());
// Retain the last dirty timestamp without overwriting it, if there is already a lease
// 如果已经有租约，则保留最后⼀个脏时间戳⽽不覆盖它
// （⽐较当前请求实例租约 和 已有租约 的LastDirtyTimestamp，选择靠后的）
if (existingLease != null && (existingLease.getHolder() != null)) {
Long existingLastDirtyTimestamp = existingLease.getHolder().getLastDirtyTimestamp();
Long registrationLastDirtyTimestamp = registrant.getLastDirtyTimestamp();
logger.debug("Existing lease found (existing={}, provided={}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);
// this is a > instead of a >= because if the timestamps are equal, we still take the remote transmitted
// InstanceInfo instead of the server local copy.
if (existingLastDirtyTimestamp > registrationLastDirtyTimestamp) {
logger.warn("There is an existing lease and the existing lease's dirty timestamp {} is greater" +
" than the one that is being registered {}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);
logger.warn("Using the existing instanceInfo instead of the new instanceInfo as the registrant");
registrant = existingLease.getHolder();
}
} else {
// The lease does not exist and hence it is a new registration
// 如果之前不存在实例的租约，说明是新实例注册
// expectedNumberOfRenewsPerMin期待的每分钟续约数+2（因为30s⼀个）
// 并更新numberOfRenewsPerMinThreshold每分钟续约阀值（85%）
synchronized (lock) {
if (this.expectedNumberOfClientsSendingRenews > 0) {
// Since the client wants to register it, increase the number of clients sending renews
this.expectedNumberOfClientsSendingRenews = this.expectedNumberOfClientsSendingRenews + 1;
updateRenewsPerMinThreshold();
}
}
logger.debug("No previous lease information found; it is new registration");
}
Lease<InstanceInfo> lease = new Lease<InstanceInfo>(registrant, leaseDuration);
if (existingLease != null) {
lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
}
gMap.put(registrant.getId(), lease);
//当前实例信息放到维护注册信息的Map
// 同步维护最近注册队列
recentRegisteredQueue.add(new Pair<Long, String>(
System.currentTimeMillis(),
registrant.getAppName() + "(" + registrant.getId() + ")"));
// This is where the initial state transfer of overridden status happens
// 如果当前实例已经维护了OverriddenStatus，将其也放到此EurekaServer的overriddenInstanceStatusMap中
if (!InstanceStatus.UNKNOWN.equals(registrant.getOverriddenStatus())) {
logger.debug("Found overridden status {} for instance {}. Checking to see if needs to be add to the "
+ "overrides", registrant.getOverriddenStatus(), registrant.getId());
if (!overriddenInstanceStatusMap.containsKey(registrant.getId())) {
logger.info("Not found overridden id {} and hence adding it", registrant.getId());
overriddenInstanceStatusMap.put(registrant.getId(), registrant.getOverriddenStatus());
}
}
// 根据overridden status规则，设置状态
InstanceStatus overriddenStatusFromMap = overriddenInstanceStatusMap.get(registrant.getId());
if (overriddenStatusFromMap != null) {
logger.info("Storing overridden status {} from map", overriddenStatusFromMap);
registrant.setOverriddenStatus(overriddenStatusFromMap);
}
// Set the status based on the overridden status rules
InstanceStatus overriddenInstanceStatus = getOverriddenInstanceStatus(registrant, existingLease, isReplication);
registrant.setStatusWithoutDirty(overriddenInstanceStatus);
// If the lease is registered with UP status, set lease service up timestamp
// 如果租约以UP状态注册，设置租赁服务时间戳
if (InstanceStatus.UP.equals(registrant.getStatus())) {
lease.serviceUp();
}
registrant.setActionType(ActionType.ADDED);//ActionType为ADD
recentlyChangedQueue.add(new RecentlyChangedItem(lease));//维护recentlyChangedQueue
registrant.setLastUpdatedTimestamp();//更新最后更新时间
// 使当前应⽤的ResponseCache失效
invalidateCache(registrant.getAppName(), registrant.getVIPAddress(), registrant.getSecureVipAddress());
logger.info("Registered instance {}/{} with status {} (replication={})",
registrant.getAppName(), registrant.getId(), registrant.getStatus(), isReplication);
} finally {
read.unlock();//释放锁
}
}
PeerAwareInstanceRegistryImpl#replicateToPeers() ：复制到Eureka对等节点
/**
* Replicates all eureka actions to peer eureka nodes except for replication
* traffic to this node.
*
*/
private void replicateToPeers(Action action, String appName, String id,
InstanceInfo info /* optional */,
InstanceStatus newStatus /* optional */, boolean isReplication) {
Stopwatch tracer = action.getTimer().start();
try {
// 如果是复制操作（针对当前节点，false）
if (isReplication) {
numberOfReplicationsLastMin.increment();
}
// If it is a replication already, do not replicate again as this will create a poison replication
// 如果它已经是复制，请不要再次复制，直接return
if (peerEurekaNodes == Collections.EMPTY_LIST || isReplication) {
return;
}
// 遍历集群所有节点（除当前节点外）
for (final PeerEurekaNode node : peerEurekaNodes.getPeerEurekaNodes()) {
// If the url represents this host, do not replicate to yourself.
if (peerEurekaNodes.isThisMyUrl(node.getServiceUrl())) {
continue;
}
// 复制Instance实例操作到某个node节点
replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node);
}
} finally {
tracer.stop();
}
}
PeerAwareInstanceRegistryImpl#replicateInstanceActionsToPeers
Eureka Server服务续约接⼝（接受客户端续约）
InstanceResource的renewLease⽅法中完成客户端的⼼跳（续约）处理，关键代码：registry.renew(app.getName(), id, isFromReplicaNode);
com.netflix.eureka.registry.PeerAwareInstanceRegistryImpl#renew
replicateInstanceActionsToPeers() 复制Instance实例操作到其它节点, 就是调用到上面的
enew()⽅法中—>leaseToRenew.renew()—>对最后更新时间戳进⾏更新
Eureka Client注册服务
启动过程：Eureka客户端在启动时也会装载很多配置类，我们通过spring-cloudnetflix-eureka-client-2.7.7.RELEASE.jar下的spring.factories⽂件可以看到加载的配置类
引⼊jar就会被⾃动装配，分析EurekaClientAutoConfiguration类头
回到主配置类EurekaClientAutoConfiguration
思考：EurekaClient启动过程要做什么事情？？？？？？
-
读取配置⽂件
-
启动时从EurekaServer获取服务实例信息
观察⽗类DiscoveryClient()，最终来到com.netflix.discovery.DiscoveryClient#DiscoveryClient(com.netflix.appinfo.ApplicationInfoManager, com.netflix.discovery.EurekaClientConfig, com.netflix.discovery.AbstractDiscoveryClientOptionalArgs, javax.inject.Provider<com.netflix.discovery.BackupRegistry>, com.netflix.discovery.shared.resolver.EndpointRandomizer)
再到com.netflix.discovery.DiscoveryClient#fetchRegistry
-
注册⾃⼰到EurekaServer（addInstance）
回到DiscoveryClient构造器
DiscoveryClient#register
底层使⽤Jersey客户端进⾏远程请求。 -
开启⼀些定时任务（⼼跳续约，刷新本地服务缓存列表）
⼼跳续约定时任务
来到com.netflix.eureka.transport.JerseyReplicationClient#sendHeartBeat
Eureka Client下架服务
我们看om.netflix.discovery.DiscoveryClient#shutdown
Eureka Client心跳续约
⼼跳续约定时任务
来到com.netflix.eureka.transport.JerseyReplicationClient#sendHeartBeat
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