前言
上一讲eureka client是如何注册的，一直跟到源码发送http请求为止，当时看eureka client注册时如此费尽，光是找一个regiter的地方就找了半天，那么client端发送了http请求给server端，server端是如何处理的呢？
带着这么一个疑问 就开始今天源码的解读了。
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源码解读
从何读起？
上一讲我们知道，跟进client注册 一直到 AbstractJersey2EurekaHttpClient.register方法，这里先看下其中的源码：
public EurekaHttpResponse<Void> register(InstanceInfo info) {
String urlPath = "apps/" + info.getAppName();
Response response = null;
try {
// 发送请求，类似于：http://localhost:8080/v2/apps/ServiceA
// 发送的是post请求，服务实例的对象被打成了一个json发送，包括自己的主机、ip、端口号
// eureka server 就知道了这个ServiceA这个服务，有一个服务实例，比如是在192.168.31.109、host-01、8761端口
Builder resourceBuilder = jerseyClient.target(serviceUrl).path(urlPath).request();
addExtraProperties(resourceBuilder);
addExtraHeaders(resourceBuilder);
response = resourceBuilder
.accept(MediaType.APPLICATION_JSON)
.acceptEncoding("gzip")
.post(Entity.json(info));
return anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
} finally {
if (logger.isDebugEnabled()) {
logger.debug("Jersey2 HTTP POST {}/{} with instance {}; statusCode={}", serviceUrl, urlPath, info.getId(),
response == null ? "N/A" : response.getStatus());
}
if (response != null) {
response.close();
}
}
}
那这种情况我们肯定可以猜测，server端应该有个controller来接收此http请求，然后默默的去做一些注册的逻辑。
紧接着我们从/apps/这个关键词入手，进行全局搜索：
全局搜索结果如下，这里可以看到很多test 调用，这里框起来的一个是不是类似于我们controller接口的调用呢？直接点进去查看，然后一步步跟进。
源码分析
接着上面说的，跟进ApplicationResource这个类，可以找到如下方法：
@Path("{appId}")
public ApplicationResource getApplicationResource(
@PathParam("version") String version,
@PathParam("appId") String appId) {
CurrentRequestVersion.set(Version.toEnum(version));
return new ApplicationResource(appId, serverConfig, registry);
}
这个appId可以理解为我们之前传递的appName，紧接着这里是直接构造了一个ApplicationResource实例，接着跟进代码，进入ApplicationResource中我们可以看到很多@GET、@POST 等restful接口，还记得上面我们register方法中，发送的http请求用的就是POST方法，所以我们这里直接看@POST请求
@POST
@Consumes({"application/json", "application/xml"})
public Response addInstance(InstanceInfo info,
@HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
logger.debug("Registering instance {} (replication={})", info.getId(), isReplication);
// validate that the instanceinfo contains all the necessary required fields
if (isBlank(info.getId())) {
return Response.status(400).entity("Missing instanceId").build();
} else if (isBlank(info.getHostName())) {
return Response.status(400).entity("Missing hostname").build();
} else if (isBlank(info.getIPAddr())) {
return Response.status(400).entity("Missing ip address").build();
} else if (isBlank(info.getAppName())) {
return Response.status(400).entity("Missing appName").build();
} else if (!appName.equals(info.getAppName())) {
return Response.status(400).entity("Mismatched appName, expecting " + appName + " but was " + info.getAppName()).build();
} else if (info.getDataCenterInfo() == null) {
return Response.status(400).entity("Missing dataCenterInfo").build();
} else if (info.getDataCenterInfo().getName() == null) {
return Response.status(400).entity("Missing dataCenterInfo Name").build();
}
// handle cases where clients may be registering with bad DataCenterInfo with missing data
DataCenterInfo dataCenterInfo = info.getDataCenterInfo();
if (dataCenterInfo instanceof UniqueIdentifier) {
String dataCenterInfoId = ((UniqueIdentifier) dataCenterInfo).getId();
if (isBlank(dataCenterInfoId)) {
boolean experimental = "true".equalsIgnoreCase(serverConfig.getExperimental("registration.validation.dataCenterInfoId"));
if (experimental) {
String entity = "DataCenterInfo of type " + dataCenterInfo.getClass() + " must contain a valid id";
return Response.status(400).entity(entity).build();
} else if (dataCenterInfo instanceof AmazonInfo) {
AmazonInfo amazonInfo = (AmazonInfo) dataCenterInfo;
String effectiveId = amazonInfo.get(AmazonInfo.MetaDataKey.instanceId);
if (effectiveId == null) {
amazonInfo.getMetadata().put(AmazonInfo.MetaDataKey.instanceId.getName(), info.getId());
}
} else {
logger.warn("Registering DataCenterInfo of type {} without an appropriate id", dataCenterInfo.getClass());
}
}
}
registry.register(info, "true".equals(isReplication));
return Response.status(204).build(); // 204 to be backwards compatible
}
由于代码不是很长，这里都给截取出来了。其实这里做的事情就很简单了。
- 做一些常规的chek，检查注册实例
InstanceInfo的一些基本信息 - DataCenter的相关操作，这里还涉及到亚马逊云，我们直接跳过
registry.register(info, "true".equals(isReplication));这里才是核心的注册，我们继续往下
public void register(final InstanceInfo info, final boolean isReplication) {
int leaseDuration = Lease.DEFAULT_DURATION_IN_SECS;
if (info.getLeaseInfo() != null && info.getLeaseInfo().getDurationInSecs() > 0) {
leaseDuration = info.getLeaseInfo().getDurationInSecs();
}
super.register(info, leaseDuration, isReplication);
replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
}
public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
try {
read.lock();
Map<String, Lease<InstanceInfo>> gMap = registry.get(registrant.getAppName());
REGISTER.increment(isReplication);
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;
}
}
Lease<InstanceInfo> existingLease = gMap.get(registrant.getId());
// Retain the last dirty timestamp without overwriting it, if there is already a lease
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
synchronized (lock) {
if (this.expectedNumberOfRenewsPerMin > 0) {
// Since the client wants to cancel it, reduce the threshold
// (1
// for 30 seconds, 2 for a minute)
this.expectedNumberOfRenewsPerMin = this.expectedNumberOfRenewsPerMin + 2;
this.numberOfRenewsPerMinThreshold =
(int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
}
}
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);
synchronized (recentRegisteredQueue) {
recentRegisteredQueue.add(new Pair<Long, String>(
System.currentTimeMillis(),
registrant.getAppName() + "(" + registrant.getId() + ")"));
}
// This is where the initial state transfer of overridden status happens
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());
}
}
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
if (InstanceStatus.UP.equals(registrant.getStatus())) {
lease.serviceUp();
}
registrant.setActionType(ActionType.ADDED);
recentlyChangedQueue.add(new RecentlyChangedItem(lease));
registrant.setLastUpdatedTimestamp();
invalidateCache(registrant.getAppName(), registrant.getVIPAddress(), registrant.getSecureVipAddress());
logger.info("Registered instance {}/{} with status {} (replication={})",
registrant.getAppName(), registrant.getId(), registrant.getStatus(), isReplication);
} finally {
read.unlock();
}
}
到了这里东西就有点多了，我们慢慢梳理。
- reda.lock() 这里使用的是读锁，方便多个服务实例同时来注册
- 这里关键信息是registry的数据结构，同时这也是保存注册实例的对象。
private final ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>> registry
= new ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>();
ConcurrentHashMap的key是appName
第二层Map的key是appId，所以数据结构格式类似于：
{
“ServiceA”: {
“001”: Lease<InstanceInfo>,
“002”: Lease<InstanceInfo>,
“003”: Lease<InstanceInfo>
},
“ServiceB”: {
“001”: Lease<InstanceInfo>
}
}
- 这里面还有两个队列
recentRegisteredQueue、recentlyChangedQueue，其中registerQueue默认保存最近1000条注册的实例信息。 - 后面就是一些状态设置之类的操作
注册表使用场景
我们注册完成之后，打开eureka 后台配置页面，可以看到自己的实例已经在页面上了，那么这个东东是如何展示的呢？
我们都知道eureka-resources模块下有很多jsp信息，点开status.jsp查看一下：
这里用到了 serverContext.getRegistry().getSortedApplications(), 然后在通过获取的Applicaiton 去执行app.getInstances()等到了所有大的服务实例信息。
这里我们还需要回头看下EurekaBootStrap中的代码，看看Application是如何来的。
从PeerAwareInstanceRegistryImpl.java的getSortedApplications()一直跟到 AbstractInstanceRegistry.java的getApplicationsFromMultipleRegions(),如下图所示：
看到这里是不是就真相大白了？
这里再总结一下：
在jsp代码中，拿到了EurekaServerContext，所以之前为什么要将这个东东放到一个Holder里面去，就是随时都要从这个里面去获取一些数据
然后会从EurekaServerContext，获取到注册表，PeerAwareInstanceRegistry，注册表，从里面获取所有的服务信息，从底层的map数据结构中，获取所有的服务注册的信息，遍历，封装到一个叫Application的东西里去，一个Application就代表了一个服务，里面包含很多个服务实例。
Eureka的服务注册流程图
申明
本文章首发自本人博客：https://www.cnblogs.com/wang-meng 和公众号：壹枝花算不算浪漫，如若转载请标明来源!
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