普通的spring boot注册到服务中心,变成服务提供者,做了2件事
1.加注解@EnableDiscoveryClient
2.指定注册中心地址
先看@EnableDiscoveryClient注解
/**
* Annotation to enable a DiscoveryClient implementation.
* @author Spencer Gibb
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {
}
注释说: 这个注解用来开启DiscoveryClient的实现
DiscoveryClient spring里面接口就搜到一个,其 实现类 有个EurekaDiscoveryClient
说明,DiscoveryClient是springcloud定义发现服务的接口,通过这个接口屏蔽了具体实现,默认用Eureka实现,也可以用其他实现替换,上层代码就不用改了
EurekaDiscoveryClient 依赖了netflix包下的EurekaClient接口,这个接口的实现类
com.netflix.discovery.DiscoveryClient才是实际干活的
得 服务url
它的类注释里面有
/**
* The class that is instrumental for interactions with Eureka Server.
....
* Eureka Client needs a configured list of Eureka Server
* {@link java.net.URL}s to talk to.
*
*
*/
说明它用到了我们配过的eureka. client.serviceUrl
找到有个方法getServiceUrlsFromConfig 但是已经废弃,被代替的是链到EndpointUtils
果然有个同名方法
/**
* Get the list of all eureka service urls from properties file for the eureka client to talk to.
*
* @param clientConfig the clientConfig to use
* @param instanceZone The zone in which the client resides
* @param preferSameZone true if we have to prefer the same zone as the client, false otherwise
* @return The list of all eureka service urls for the eureka client to talk to
*/
public static List getServiceUrlsFromConfig(EurekaClientConfig clientConfig, String instanceZone, boolean preferSameZone) {
List orderedUrls = new ArrayList();
//找到配置的region,没有配置就默认
String region = getRegion(clientConfig);
//找到这个region下的所有zone
String[] availZones = clientConfig.getAvailabilityZones(clientConfig.getRegion());
if (availZones == null || availZones.length == 0) {
availZones = new String[1];
//没有配的话,还是用那个默认的zone
//就是我们经常配的eureka. client.serviceUrl.defaultZone
availZones[0] = DEFAULT_ZONE;
}
logger.debug("The availability zone for the given region {} are {}", region, Arrays.toString(availZones));
//根据传入的参数(当前服务所在zone,是不是同zone优先,所有zone),
//按某算法决定先用哪个zone(先放入结果集)
int myZoneOffset = getZoneOffset(instanceZone, preferSameZone, availZones);
//clientConfig.getEurekaServerServiceUrls 如果这个zone没有配url就返回eureka. client.serviceUrl.defaultZone的url
List serviceUrls = clientConfig.getEurekaServerServiceUrls(availZones[myZoneOffset]);
if (serviceUrls != null) {
orderedUrls.addAll(serviceUrls);
}
int currentOffset = myZoneOffset == (availZones.length - 1) ? 0 : (myZoneOffset + 1);
while (currentOffset != myZoneOffset) {
serviceUrls = clientConfig.getEurekaServerServiceUrls(availZones[currentOffset]);
if (serviceUrls != null) {
orderedUrls.addAll(serviceUrls);
}
if (currentOffset == (availZones.length - 1)) {
currentOffset = 0;
} else {
currentOffset++;
}
}
if (orderedUrls.size() < 1) {
throw new IllegalArgumentException("DiscoveryClient: invalid serviceUrl specified!");
}
return orderedUrls;
}
可以看出,决定serviceUrl的优先级是,先看有没有配region(没有就用默认值),再看这个region下的多个zone(一个都没有就用我配的defaultZone),按某算法(可能是本zone优先)决定先加入结果集的zone,任何顺序一一加入
服务注册
com.netflix.discovery.DiscoveryClient的类注释里面还有
Eureka Client is responsible for
a)Registeringthe instance with Eureka Server
注册服务到注册中心也在这个类.可以看到几个构造器的重载最终会调用到initScheduledTasks();
里面读取了我们设的eureka.client.register-with-eureka要不要注册到服务中心
if (clientConfig.shouldRegisterWithEureka()) {
/.........
// InstanceInfo replicator 一个定时任务
instanceInfoReplicator = new InstanceInfoReplicator(
this,
instanceInfo,
clientConfig.getInstanceInfoReplicationIntervalSeconds(),
2); // burstSize
/......
//执行这个定时任务
instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
}
这个定时任务里面执行的是
public void run() {
try {
discoveryClient.refreshInstanceInfo();
Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
if (dirtyTimestamp != null) {
//找到触发 注册的地方了!!!
discoveryClient.register();
instanceInfo.unsetIsDirty(dirtyTimestamp);
}
} catch (Throwable t) {
logger.warn("There was a problem with the instance info replicator", t);
} finally {
Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
scheduledPeriodicRef.set(next);
}
}
discoveryClient.register();是以下这个,方法注释写 注册是REST请求方式进行的
/**
* Register with the eureka service by making the appropriate REST call.
*/
boolean register() throws Throwable {
logger.info(PREFIX + appPathIdentifier + ": registering service...");
EurekaHttpResponse httpResponse;
try {
//注册时 客户端传过来的 服务元数据
httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
} catch (Exception e) {
logger.warn("{} - registration failed {}", PREFIX + appPathIdentifier, e.getMessage(), e);
throw e;
}
if (logger.isInfoEnabled()) {
logger.info("{} - registration status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());
}
return httpResponse.getStatusCode() == 204;
}
服务续
续必定是已经注册了 在注册的if里面 有个心跳定时任务
/...
// Heartbeat timer
scheduler.schedule(
new TimedSupervisorTask(
"heartbeat",
scheduler,
heartbeatExecutor,
renewalIntervalInSecs,
TimeUnit.SECONDS,
expBackOffBound,
new HeartbeatThread()//定时执行这个的run
),
renewalIntervalInSecs, TimeUnit.SECONDS);
/......
// InstanceInfo replicator
}
/**
* The heartbeat task that renews the lease in the given intervals.
*/
private class HeartbeatThread implements Runnable {
public void run() {
if (renew()) {//都在 renew
lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
}
}
}
/**
* Renew with the eureka service by making the appropriate REST call
*/
boolean renew() {
EurekaHttpResponse httpResponse;
try {
//直接REST请求方式续约
httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
logger.debug("{} - Heartbeat status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());
//不正常
if (httpResponse.getStatusCode() == 404) {
REREGISTER_COUNTER.increment();
logger.info("{} - Re-registering apps/{}", PREFIX + appPathIdentifier, instanceInfo.getAppName());
return register();
}
//正常
return httpResponse.getStatusCode() == 200;
} catch (Throwable e) {
logger.error("{} - was unable to send heartbeat!", PREFIX + appPathIdentifier, e);
return false;
}
}
服务获取
定时任务initScheduledTasks里面 还有服务获取
private void initScheduledTasks() {
//eureka.client.fetch-registry配置 默认true
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer
//去配置里面拿 默认30s
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
scheduler.schedule(
new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
),
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
REST请求的定义
所有交换都是通过REST请求
com.netflix.eureka.resources包的ApplicationResource为例
@POST
@Consumes({"application/json", "application/xml"})
public Response addInstance(InstanceInfo info,
@HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
//.....一堆校验
registry.register(info, "true".equals(isReplication));
return Response.status(204).build(); // 204 to be backwards compatible
}
@Override
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();
}
//父类中的注册实现,把info存在一个2层map里面,第一层key是服务名.第二层key是元数据的id
super.register(info, leaseDuration, isReplication);
//向其他注册中心复制
replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
}