介绍下Eureka的使用以及相关配置参数

高可用

服务调用

1.使用原始的Eureka DiscoveryClient 来找到服务实例的主机并且用Spring的RestTemplate来发起调用。 2.使用Ribbon，一个使用Eureka来找到服务实例的客户端负载均衡解决方案 3. 使用Feigin，它使用了一个说明性的方法来调用服务。它内部使用了Ribbo

源码

服务端

服务端启动

EurekaServerInitializerConfiguration.start()

try {
//TODO: is this class even needed now?
eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext);
log.info("Started Eureka Server");
publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));
EurekaServerInitializerConfiguration.this.running = true;
publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
}
catch (Exception ex) {
// Help!
log.error("Could not initialize Eureka servlet context", ex);
}

复制 neighboring eureka node

// Copy registry from neighboring eureka node
int registryCount = this.registry.syncUp();

计算Renews threshold (numberOfRenewsPerMinThreshold)

公式: 2 * N * 0.85 ==> 60/心跳时间(总是认为是30s)*instance num *factor Netflix code assumes that heartbeats are always received at intervals of 30 seconds for this calculation.

1.初始化 numberOfRenewsPerMinThreshold PeerAwareInstanceRegistryImpl

@Override
//count 来自 this.registry.syncUp();
public void openForTraffic(ApplicationInfoManager applicationInfoManager, int count) {
// Renewals happen every 30 seconds and for a minute it should be a factor of 2.
this.expectedNumberOfRenewsPerMin = count * 2;
// serverConfig.getRenewalPercentThreshold() 来自配置 默认0.85
this.numberOfRenewsPerMinThreshold =
(int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
logger.info("Got " + count + " instances from neighboring DS node");
logger.info("Renew threshold is: " + numberOfRenewsPerMinThreshold);
this.startupTime = System.currentTimeMillis();
if (count > 0) {
this.peerInstancesTransferEmptyOnStartup = false;
}
DataCenterInfo.Name selfName = applicationInfoManager.getInfo().getDataCenterInfo().getName();
boolean isAws = Name.Amazon == selfName;
if (isAws && serverConfig.shouldPrimeAwsReplicaConnections()) {
logger.info("Priming AWS connections for all replicas..");
primeAwsReplicas(applicationInfoManager);
}
logger.info("Changing status to UP");
applicationInfoManager.setInstanceStatus(InstanceStatus.UP);
super.postInit();
}

2.客户端注册时候刷新numberOfRenewsPerMinThreshold

AbstractInstanceRegistry
// 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");

3.renewal-threshold-update-interval-ms 时间间隔后从新计算阀值.

接收客户端的rest 请求 DiscoveryJerseyProvider

@Override
public Object readFrom(Class serializableClass, Type type,
Annotation[] annotations, MediaType mediaType,
MultivaluedMap headers, InputStream inputStream) throws IOException {
DecoderWrapper decoder;
if (MediaType.MEDIA_TYPE_WILDCARD.equals(mediaType.getSubtype())) {
decoder = xmlDecoder;
} else if ("json".equalsIgnoreCase(mediaType.getSubtype())) {
decoder = jsonDecoder;
} else {
decoder = xmlDecoder; // default
}
try {
return decoder.decode(inputStream, serializableClass);
} catch (Throwable e) {
if (e instanceof Error) { // See issue: https://github.com/Netflix/eureka/issues/72 on why we catch Error here.
closeInputOnError(inputStream);
throw new WebApplicationException(createErrorReply(500, e, mediaType));
}
LOGGER.debug("Cannot parse request body", e);
throw new WebApplicationException(createErrorReply(400, "cannot parse request body", mediaType));
}
}

EvictionTask

以eviction-interval-timer-in-ms (eureka.server.evictionIntervalTimerInMs)指定的频率执行 移除过期的instacne.在移除之前检查是否进入自我保护模式.(Renews < Renews threshold && eureka.server.enableSelfPreservation=true)

Renews (last min)

每分钟计算一次.

客户端