遇見的問題：
在啓動eureka服務的時候，正常，再啓動網關組件的時候，出現如下錯誤：
2020-04-15 11:04:07.514 WARN 26540 --- [ main] com.netflix.discovery.DiscoveryClient : Using default backup registry implementation which does not do anything.
2020-04-15 11:04:07.517 INFO 26540 --- [ main] com.netflix.discovery.DiscoveryClient : Starting heartbeat executor: renew interval is: 5
2020-04-15 11:04:07.523 INFO 26540 --- [ main] c.n.discovery.InstanceInfoReplicator : InstanceInfoReplicator onDemand update allowed rate per min is 4
2020-04-15 11:04:07.532 INFO 26540 --- [ main] com.netflix.discovery.DiscoveryClient : Discovery Client initialized at timestamp 1586919847529 with initial instances count: 0
2020-04-15 11:04:07.542 INFO 26540 --- [ main] o.s.c.n.e.s.EurekaServiceRegistry : Registering application MSS-GATEWAY with eureka with status UP
2020-04-15 11:04:07.543 INFO 26540 --- [ main] com.netflix.discovery.DiscoveryClient : Saw local status change event StatusChangeEvent [timestamp=1586919847543, current=UP, previous=STARTING]
2020-04-15 11:04:07.545 INFO 26540 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient : DiscoveryClient_MSS-GATEWAY/localhost:mss-gateway:9030: registering service...
2020-04-15 11:04:07.551 INFO 26540 --- [ main] o.s.c.support.DefaultLifecycleProcessor : Starting beans in phase 2147483647
2020-04-15 11:04:07.553 INFO 26540 --- [ main] d.s.w.p.DocumentationPluginsBootstrapper : Context refreshed
2020-04-15 11:04:07.558 ERROR 26540 --- [nfoReplicator-0] c.n.d.s.t.d.RedirectingEurekaHttpClient : Request execution error
com.sun.jersey.api.client.ClientHandlerException: java.net.UnknownHostException: eureka-server
at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:187) ~[jersey-apache-client4-1.19.1.jar:1.19.1]
at com.sun.jersey.api.client.filter.GZIPContentEncodingFilter.handle(GZIPContentEncodingFilter.java:123) ~[jersey-client-1.19.1.jar:1.19.1]
at com.netflix.discovery.EurekaIdentityHeaderFilter.handle(EurekaIdentityHeaderFilter.java:27) ~[eureka-client-1.9.3.jar:1.9.3]
at com.sun.jersey.api.client.Client.handle(Client.java:652) ~[jersey-client-1.19.1.jar:1.19.1]
at com.sun.jersey.api.client.WebResource.handle(WebResource.java:682) ~[jersey-client-1.19.1.jar:1.19.1]
at com.sun.jersey.api.client.WebResource.access$200(WebResource.java:74) ~[jersey-client-1.19.1.jar:1.19.1]
at com.sun.jersey.api.client.WebResource$Builder.post(WebResource.java:570) ~[jersey-client-1.19.1.jar:1.19.1]
at com.netflix.discovery.shared.transport.jersey.AbstractJerseyEurekaHttpClient.register(AbstractJerseyEurekaHttpClient.java:56) ~[eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.MetricsCollectingEurekaHttpClient.execute(MetricsCollectingEurekaHttpClient.java:73) ~[eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.RedirectingEurekaHttpClient.executeOnNewServer(RedirectingEurekaHttpClient.java:118) ~[eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.RedirectingEurekaHttpClient.execute(RedirectingEurekaHttpClient.java:79) ~[eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:120) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.DiscoveryClient.register(DiscoveryClient.java:829) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.InstanceInfoReplicator.run(InstanceInfoReplicator.java:121) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.InstanceInfoReplicator$1.run(InstanceInfoReplicator.java:101) [eureka-client-1.9.3.jar:1.9.3]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [na:1.8.0_121]
at java.util.concurrent.FutureTask.run(Unknown Source) [na:1.8.0_121]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(Unknown Source) [na:1.8.0_121]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source) [na:1.8.0_121]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [na:1.8.0_121]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [na:1.8.0_121]
at java.lang.Thread.run(Unknown Source) [na:1.8.0_121]
Caused by: java.net.UnknownHostException: eureka-server
at java.net.InetAddress.getAllByName0(Unknown Source) ~[na:1.8.0_121]
at java.net.InetAddress.getAllByName(Unknown Source) ~[na:1.8.0_121]
at java.net.InetAddress.getAllByName(Unknown Source) ~[na:1.8.0_121]
at org.apache.http.impl.conn.SystemDefaultDnsResolver.resolve(SystemDefaultDnsResolver.java:45) ~[httpclient-4.5.6.jar:4.5.6]
at org.apache.http.impl.conn.DefaultClientConnectionOperator.resolveHostname(DefaultClientConnectionOperator.java:263) ~[httpclient-4.5.6.jar:4.5.6]
at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:162) ~[httpclient-4.5.6.jar:4.5.6]
at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:144) ~[httpclient-4.5.6.jar:4.5.6]
at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:134) ~[httpclient-4.5.6.jar:4.5.6]
at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:610) ~[httpclient-4.5.6.jar:4.5.6]
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:445) ~[httpclient-4.5.6.jar:4.5.6]
at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:835) ~[httpclient-4.5.6.jar:4.5.6]
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:118) ~[httpclient-4.5.6.jar:4.5.6]
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56) ~[httpclient-4.5.6.jar:4.5.6]
at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:173) ~[jersey-apache-client4-1.19.1.jar:1.19.1]
... 30 common frames omitted
2020-04-15 11:04:07.560 WARN 26540 --- [nfoReplicator-0] c.n.d.s.t.d.RetryableEurekaHttpClient : Request execution failed with message: java.net.UnknownHostException: eureka-server
2020-04-15 11:04:07.560 WARN 26540 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient : DiscoveryClient_MSS-GATEWAY/localhost:mss-gateway:9030 - registration failed Cannot execute request on any known server
com.netflix.discovery.shared.transport.TransportException: Cannot execute request on any known server
at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:112) ~[eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) ~[eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) ~[eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77) ~[eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) ~[eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.DiscoveryClient.register(DiscoveryClient.java:829) ~[eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.InstanceInfoReplicator.run(InstanceInfoReplicator.java:121) [eureka-client-1.9.3.jar:1.9.3]
at com.netflix.discovery.InstanceInfoReplicator$1.run(InstanceInfoReplicator.java:101) [eureka-client-1.9.3.jar:1.9.3]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) [na:1.8.0_121]
at java.util.concurrent.FutureTask.run(Unknown Source) [na:1.8.0_121]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(Unknown Source) [na:1.8.0_121]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source) [na:1.8.0_121]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [na:1.8.0_121]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [na:1.8.0_121]
at java.lang.Thread.run(Unknown Source) [na:1.8.0_121]
錯誤日誌摘要：
-
com.sun.jersey.api.client.ClientHandlerException: java.net.UnknownHostException: eureka-server
-
com.netflix.discovery.shared.transport.TransportException: Cannot execute request on any known server
在eureka服務端的配置如下（部分）：
eureka:
instance:
#hostname: 127.0.0.1
hostname: eureka-server
client:
registerWithEureka: false
fetchRegistry: false
serviceUrl:
defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/
在網關中的配置如下（部分）：
eureka:
instance:
lease-renewal-interval-in-seconds: 5
lease-expiration-duration-in-seconds: 10
client:
service-url:
#defaultZone: http://127.0.0.1:9010/eureka/
defaultZone: http://eureka-server:9010/eureka/
問題原因：
在其他配置都正常的情況，我出現了這種問題，經排查其實是eureka服務端的eureka-instance-hostname命名，沒有在C:\Windows\System32\drivers\etc\hosts文件進行配置造成的。
解決方法：
第一種： 在C:\Windows\System32\drivers\etc\hosts文件中添加實例名和IP地址的映射關係，如下圖所示：
第二種： 如果不想配置這個映射，可以選擇使用IP地址作爲eureka-instance-hostname屬性的值，這樣也可以直接使用（之前就是這樣使用的，所以一直沒有遇見該問題），即上面配置中註釋掉的代碼，需要把服務端和網關中的配置都修改了纔可以。