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下面主要分为Client端和Server端两大类进行简述，Eureka的几个核心参数

客户端参数

Client端的核心参数

参数	默认值	说明
eureka.client.availability-zones		告知Client有哪些region以及availability-zones，支持配置修改运行时生效
eureka.client.filter-only-up-instances	true	是否过滤出InstanceStatus为UP的实例
eureka.client.region	us-east-1	指定该应用实例所在的region，AWS datacenters适用
eureka.client.register-with-eureka	true	是否将该应用实例注册到Eureka Server
eureka.client.prefer-szme-zone-eureka	true	是否优先使用与该实例处于相同zone的Eureka Server
eureka.client.on-demand-update-status-change	true	是够将本地实例状态更新通过ApplicationInfoManager实时触发同步到Eureka Server
eureka.instance.metadata-map		指定应用实例的元数据信息
eureka.instance.prefer-ip-address	false	指定优先使用ip地址替代host name作为实例的hostName字段值
eureka.instance.lease-expiration-duration-in-seconds	90	指定Eureka Client间隔多久需要向Eureka Server发送心跳来告知Eureka Server该实例还存活

定时任务参数

参数	默认值	说明
eureka.client.cache-refresh-executor-thread-pool-size	2	刷新缓存的CacheRefreshThread的线程池大小
eureka.client.cache-refresh-executor-exponential-back-off-bound	10	(刷新缓存)调度任务执行超时时下次的调度的延迟时间
reka.client.heartbeat-executor-thread-pool-size	2	心跳线程HeartBeatThread的线程池大小
eureka.client.heartbeat-executor-exponential-back-off-bound	10	(心跳执行)调度任务超时时下次的调度的延时时间
eureka.client.registry-fetch-interval-seconds	30	CacheRefreshThread线程调度频率
eureka.client.eureka-service-url-poll-interval-seconds	5*60	AsyncResolver.updateTask刷新Eureka Server地址的时间间隔
eureka.client.initial-instance-info-replication-interval-seconds	40	InstanceInfoReplicator将实例信息变更同步到Eureka Server的初始延时时间
eureka.client.instance-info-replication-interval-seconds	30	InstanceInfoReplicator将实例信息变更同步到Eureka Server的时间间隔
ureka.instance.lease-renewal-interval-in-seconds	30	Eureka Client向Eureka Server发送心跳的时间间隔

http参数

Eureka Client底层httpClient与Eureka Server通信，提供的先关参数

参数	默认值	说明
eureka.client.eureka-server-connect-timeout-seconds	5	连接超时时间
eureka.client.eureka-server-read-timeout-seconds	8	读超时时间
eureka.client.eureka-server-total-connections	200	连接池最大活动连接数
eureka.client.eureka-server-total-connections-per-host	50	每个host能使用的最大链接数
eureka.client.eureka-connection-idle-timeout-seconds	30	连接池中链接的空闲时间

服务端端参数

主要包含这几类：基本参数、response cache参数、peer相参数、http参数

基本参数

参数	默认值	说明
eureka.server.enable-self-perservation	true	是否开启自我保护模式
eureka.server.renewal-percent-threshold	0.85	指定每分钟需要收到续约次数的阈值
eureka.instance.registry.expected-number-of-renews-per-min	1	指定每分钟需要接收到的续约次数值，实际该值在其中被写死为count*2，另外也会被更新
eureka.server.renewal-threshold-update-interval-ms	15分钟	指定updateRenewalThreshold定时任务的调度频率，来动态更新expectedNumberOfRenewsPerMin及numberOfRenewsPerminThreshold值
eureka.server.eviction-interval-timer-in-ms	60*1000	指定EvictionTask定时任务的调度频率，用于剔除过期的实例

response cache参数

Eureka Server为了提升自身REST API接口的性能，提供了两个缓存：一个是基于ConcurrentMap的readOnlyCacheMap，一个是基于Guava Cache的readWriteCacheMap。其相关参数如下：

参数	默认值	说明
eureka.server.use-read-only-response-cache	true	是否使用只读的response-cache
eureka.server.response-cache-update-interval-ms	30*1000	设置CacheUpdateTask的调度时间间隔，用于从readWriteCacheMap更新数据到readOnlyCacheMap。仅仅在eureka.server.use-read-only-response-cache为true的时候生效
eureka.server.response-cache-auto-expiration-in-seconds	180	设置readWriteCacheMap的expireAfterWrite参数，指定写入多长时间过过期

peer相关参数

参数	默认值	说明
eureka.server.peer-eureka-nodes-update-interval-ms	10分钟	指定peersUpdateTask调度的时间间隔，用于从配置文件刷新peerEurekaNodes节点的配置信息(‘eureka.client.serviceUrl相关zone的配置’)
eureka.server.peer-eureka-status-refresh-time-interval-ms	30*1000	指定更新peer node状态信息的时间间隔

http参数

Eureka Server需要与其他peer节点进行通信，复制实例信息，其底层使用httpClient，提供相关的参数

参数	默认值	说明
eureka.server.peer-node-connect-timeout-ms	200	连接超时时间
eureka.server.peer-node-read-timeout-ms	200	读超时时间
eureka.server.peer-node-total-connections	1000	连接池最大活动连接数
eureka.server.peer-node-total-connections-per-host	500	每个host能使用的最大连接数
eureka.server.peer-node-connection-idle-timeout-seconds	30	连接池中连接的空闲时间

参数调优

常见问题

1.为什么服务下线了，Eureka Server接口返回的信息还会存在？

2.为什么服务上线了，Eureka Client不能及时获取到？

3.为什么会有一下提示：

EMERGENCY!EUREKA MAY BE INCORRECTLY CLAIMING INSTANCES ARE UP WHEN THEY’RE NOT. RENEWALS ARE LESSER THAN THRESHOLD AND HENCE THE INSTANCES ARE NOT BEING EXPIRED JUST TO BE SAFE

解决方法：

1.Eureka Server并不是强一致的，因此registry中会议保留过期的实例信息。原因如下：

• 应用实例异常挂掉，没能在挂掉之前告知Eureka Server要下线掉该服务实例信息。这个就需要依赖Eureka Server的EvictionTask去剔除。
• 应用实例下线是有告知Eureka Server下线，但是由于Eureka Server的REST API有response cache，因此需要等待缓存过期才能更新。
• 由于Eureka Server开启并以入了SELF PRESERVATION(自我保护)模式，导致registry的信息不会因为过期而被剔除掉，直到退出SELF PRESERVATION(自我保护)模式。

针对Client下线而没有通知Eureka Server的问题，可以调整EvictionTask的调度频率，比如把默认的时间间隔60s，调整为5s：

eureka:server:eviction-interval-timer-in-ms: 5000

针对response cache的问题，可以根据情况考虑关闭readOnlyCacheMap：

eureka:server:use-read-only-response-cache: false

或者调整readWriteCacheMap的过期时间：

eureka:server:response-cache-auto-expiration-in-seconds: 60

针对SELF PRESERVATION(自我保护)的问题，在测试环境可以将enable-self-preservation设置为false：

eureka:server:enable-self-preservation: false

关闭之后会提示：

THE SELF PRESER VAT ION MODE IS TURNED OFF.  THIS MAY NOT PRO TECT INSTANCE EXPIRY IN CASE OF NETWORK/OTHER PROBLEMS.

或者：

RENEWALS ARE LESSER THAN THE THRESHOLD.THE SELF PRESERVATION MODE IS TURNED OFF.THIS MAY  NOT PROTECT INSTANCE EXPIRY IN CASE OF NETWORK/OTHER PROBLEMS.

2.针对新服务上线，Eureka Client获取不及时的问题，在测试环境，可以适当提高client端拉取Server注册信息的频率，例如下面将默认的30s改为5s：

eureka:client:registry-fetch-interval-seconds: 5

3.在实际生产过程中，经常会有网络抖动等问题造成服务实例与Eureka Server的心跳未能如期保持，但是服务实例本身是健康的，这个时候如果按照租约剔除机制剔除的话，会造成误判无果大范围误判的话，可能导致整个服务注册列表的大部分注册信息被删除，从而没有可用服务。Eureka为了解决这个问题引入了SELF PRESERVATION机制，当最近一分钟接收到的租约次数小于等于指定阈值的话，则关闭租约失效剔除，禁止定时任务失效的实例，从而保护注册信息。

在生产环境下，可以吧renewwalPercentThreshold及leaseRenewalIntervalInSeconds参数调小一点，从而提高触发SELF PRESERVATION机制的阈值。

eureka:instance:lease-renewal-interval-in-seconds: 10 #默认是30renewal-percent-threshold: 0.49       #默认是0.85

监控指标

Eureka内置了基于servo的指标统计，具体在com.netflix.eureka.util.EurekaMonitors。Spring Boot 2.x版本改为使用Micrometer，不再支持Neflix Servo，转而支持Neflix Servo的替代品Neflix Spectator。不过对于Servo，可以通过DefaultMonitorRegistry.getInstance().getRegisteredMonitors来获取所有注册了的Monitor，进而获取其指标值。

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//package com.netflix.eureka.util;import com.netflix.appinfo.AmazonInfo;
import com.netflix.appinfo.ApplicationInfoManager;
import com.netflix.appinfo.DataCenterInfo;
import com.netflix.appinfo.AmazonInfo.MetaDataKey;
import com.netflix.appinfo.DataCenterInfo.Name;
import com.netflix.servo.DefaultMonitorRegistry;
import com.netflix.servo.annotations.DataSourceType;
import com.netflix.servo.annotations.Monitor;
import com.netflix.servo.monitor.Monitors;
import java.util.concurrent.atomic.AtomicLong;public enum EurekaMonitors {// 自启动以来收到的总续约次数RENEW("renewCounter", "Number of total renews seen since startup"),// 自启动以来收到的总取消租约次数CANCEL("cancelCounter", "Number of total cancels seen since startup"),// 自启动以来查询registry的总次数GET_ALL_CACHE_MISS("getAllCacheMissCounter", "Number of total registery queries seen since startup"),// 自启动以来delta查询registry的总次数GET_ALL_CACHE_MISS_DELTA("getAllCacheMissDeltaCounter", "Number of total registery queries for delta seen since startup"),// 自启动以来使用remote region查询registry的总次数GET_ALL_WITH_REMOTE_REGIONS_CACHE_MISS("getAllWithRemoteRegionCacheMissCounter", "Number of total registry with remote region queries seen since startup"),// 自启动以来使用remote region及delta方式查询registry的总次数GET_ALL_WITH_REMOTE_REGIONS_CACHE_MISS_DELTA("getAllWithRemoteRegionCacheMissDeltaCounter", "Number of total registry queries for delta with remote region seen since startup"),// 自启动以来查询delta的总次数GET_ALL_DELTA("getAllDeltaCounter", "Number of total deltas since startup"),// 自启动以来传递regions查询delta的总次数GET_ALL_DELTA_WITH_REMOTE_REGIONS("getAllDeltaWithRemoteRegionCounter", "Number of total deltas with remote regions since startup"),// 自启动以来查询'/{version}/apps'的次数GET_ALL("getAllCounter", "Number of total registry queries seen since startup"),// 自启动以来传递regions参数查询'/{version}/apps'的次数GET_ALL_WITH_REMOTE_REGIONS("getAllWithRemoteRegionCounter", "Number of total registry queries with remote regions, seen since startup"),// 自启动以来请求/{version}/apps/{appId}的总次数GET_APPLICATION("getApplicationCounter", "Number of total application queries seen since startup"),// 自启动以来register的总次数REGISTER("registerCounter", "Number of total registers seen since startup"),// 自启动以来剔除过期实例的总次数EXPIRED("expiredCounter", "Number of total expired leases since startup"),// 自启动以来statusUpdate的总次数STATUS_UPDATE("statusUpdateCounter", "Number of total admin status updates since startup"),// 自启动以来deleteStatusOverride的总次数STATUS_OVERRIDE_DELETE("statusOverrideDeleteCounter", "Number of status override removals"),// 自启动以来收到cancel请求时对应实例找不到的次数CANCEL_NOT_FOUND("cancelNotFoundCounter", "Number of total cancel requests on non-existing instance since startup"),// 自启动以来收到renew请求时对应实例找不到的次数RENEW_NOT_FOUND("renewNotFoundexpiredCounter", "Number of total renew on non-existing instance since startup"),REJECTED_REPLICATIONS("numOfRejectedReplications", "Number of replications rejected because of full queue"),FAILED_REPLICATIONS("numOfFailedReplications", "Number of failed replications - likely from timeouts"),// 由于开启rate limiter被丢弃的请求数量RATE_LIMITED("numOfRateLimitedRequests", "Number of requests discarded by the rate limiter"),// 如果开启rate limiter的话，将被丢弃的请求数RATE_LIMITED_CANDIDATES("numOfRateLimitedRequestCandidates", "Number of requests that would be discarded if the rate limiter's throttling is activated"),// 开启rate limiter时请求全量registry被丢弃的请求数RATE_LIMITED_FULL_FETCH("numOfRateLimitedFullFetchRequests", "Number of full registry fetch requests discarded by the rate limiter"),// 如果开启rate limiter时请求全量registry将被丢弃的请求数RATE_LIMITED_FULL_FETCH_CANDIDATES("numOfRateLimitedFullFetchRequestCandidates", "Number of full registry fetch requests that would be discarded if the rate limiter's throttling is activated");private final String name;private final String myZoneCounterName;private final String description;@Monitor(name = "count",type = DataSourceType.COUNTER)private final AtomicLong counter = new AtomicLong();@Monitor(name = "count-minus-replication",type = DataSourceType.COUNTER)private final AtomicLong myZoneCounter = new AtomicLong();private EurekaMonitors(String name, String description) {this.name = name;this.description = description;DataCenterInfo dcInfo = ApplicationInfoManager.getInstance().getInfo().getDataCenterInfo();if (dcInfo.getName() == Name.Amazon) {this.myZoneCounterName = ((AmazonInfo)dcInfo).get(MetaDataKey.availabilityZone) + "." + name;} else {this.myZoneCounterName = "dcmaster." + name;}}public void increment() {this.increment(false);}public void increment(boolean isReplication) {this.counter.incrementAndGet();if (!isReplication) {this.myZoneCounter.incrementAndGet();}}public String getName() {return this.name;}public String getZoneSpecificName() {return this.myZoneCounterName;}public String getDescription() {return this.description;}public long getCount() {return this.counter.get();}public long getZoneSpecificCount() {return this.myZoneCounter.get();}public static void registerAllStats() {EurekaMonitors[] var0 = values();int var1 = var0.length;for(int var2 = 0; var2 < var1; ++var2) {EurekaMonitors c = var0[var2];Monitors.registerObject(c.getName(), c);}}public static void shutdown() {EurekaMonitors[] var0 = values();int var1 = var0.length;for(int var2 = 0; var2 < var1; ++var2) {EurekaMonitors c = var0[var2];DefaultMonitorRegistry.getInstance().unregister(Monitors.newObjectMonitor(c.getName(), c));}}
}