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Api calls via gateway throws java.net.UnknownHostException even though I am able to hit the application directly with the given hostname
Spring Boot version : 2.4.2
Spring-cloud.version: 2020.0.1
Java version: 11
Note: Samething works with spring boot 2.3.8.RELEASE and cloud version: Hoxton.SR9 with Java 8
Logs:
2021-02-10 14:25:05.398 ERROR 12632 --- [ctor-http-nio-4] a.w.r.e.AbstractErrorWebExceptionHandler : [efcc81fd-3] 500 Server Error for HTTP GET "/sample-order-service/sample-order"
java.net.UnknownHostException: failed to resolve 'MY-COMPUTER-NAME' after 2 queries
at io.netty.resolver.dns.DnsResolveContext.finishResolve(DnsResolveContext.java:1013) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException:
Error has been observed at the following site(s):
|_ checkpoint ⇢ org.springframework.cloud.gateway.filter.WeightCalculatorWebFilter [DefaultWebFilterChain]
|_ checkpoint ⇢ HTTP GET "/sample-order-service/sample-order" [ExceptionHandlingWebHandler]
Stack trace:
at io.netty.resolver.dns.DnsResolveContext.finishResolve(DnsResolveContext.java:1013) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
at io.netty.resolver.dns.DnsResolveContext.tryToFinishResolve(DnsResolveContext.java:966) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
at io.netty.resolver.dns.DnsResolveContext.query(DnsResolveContext.java:414) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
at io.netty.resolver.dns.DnsResolveContext.onResponse(DnsResolveContext.java:625) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
at io.netty.resolver.dns.DnsResolveContext.access$400(DnsResolveContext.java:63) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
at io.netty.resolver.dns.DnsResolveContext$2.operationComplete(DnsResolveContext.java:458) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
at io.netty.util.concurrent.DefaultPromise.notifyListener0(DefaultPromise.java:578) ~[netty-common-4.1.58.Final.jar:4.1.58.Final]
at io.netty.util.concurrent.DefaultPromise.notifyListeners0(DefaultPromise.java:571) ~[netty-common-4.1.58.Final.jar:4.1.58.Final]
at io.netty.util.concurrent.DefaultPromise.notifyListenersNow(DefaultPromise.java:550) ~[netty-common-4.1.58.Final.jar:4.1.58.Final]
at io.netty.util.concurrent.DefaultPromise.notifyListeners(DefaultPromise.java:491) ~[netty-common-4.1.58.Final.jar:4.1.58.Final]
at io.netty.util.concurrent.DefaultPromise.setValue0(DefaultPromise.java:616) ~[netty-common-4.1.58.Final.jar:4.1.58.Final]
at io.netty.util.concurrent.DefaultPromise.setSuccess0(DefaultPromise.java:605) ~[netty-common-4.1.58.Final.jar:4.1.58.Final]
at io.netty.util.concurrent.DefaultPromise.trySuccess(DefaultPromise.java:104) ~[netty-common-4.1.58.Final.jar:4.1.58.Final]
at io.netty.resolver.dns.DnsQueryContext.trySuccess(DnsQueryContext.java:201) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
at io.netty.resolver.dns.DnsQueryContext.finish(DnsQueryContext.java:193) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
at io.netty.resolver.dns.DnsNameResolver$DnsResponseHandler.channelRead(DnsNameResolver.java:1230) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103) ~[netty-codec-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.nio.AbstractNioMessageChannel$NioMessageUnsafe.read(AbstractNioMessageChannel.java:93) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:719) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493) ~[netty-transport-4.1.58.Final.jar:4.1.58.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989) ~[netty-common-4.1.58.Final.jar:4.1.58.Final]
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.58.Final.jar:4.1.58.Final]
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-common-4.1.58.Final.jar:4.1.58.Final]
at java.base/java.lang.Thread.run(Thread.java:834) ~[na:an]
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By SFG Contributor November 27, 2020 Spring, Spring Boot, Spring Cloud Using API Gateways is a common design pattern with microservice architectures. API Gateways allow you to abstract the underlying implementation of the microservices. Microservices based systems typically have a large number of independent services.
The API Gateway Service is a Spring Boot application that routes client requests to the Message service. file. The code to add the Netflix Zuul dependency is: main class to enable Zuul. annotation enables all the features of the Zull API Gateway.
This project provides a library for building an API Gateway on top of Spring WebFlux. Spring Cloud Gateway aims to provide a simple, yet effective way to route to APIs and provide cross cutting concerns to them such as: security, monitoring/metrics, and resiliency.
The API Gateway Service. The API Gateway Service is a Spring Boot application that routes client requests to the Message service. As we will use Netflix Zuul as the API Gateway implementation, we first need to add the dependency of Netflix Zuul in the pom.xml file. The code to add the Netflix Zuul dependency is:
Add this config to your microservice
eureka.instance.hostname=localhost
This bugged me a lot and seemed to be a problem with the Netty and Spring Boot 2.4.x.
But I managed to fix this problem by using the reactor.netty.http.client.HttpClient with DefaultAddressResolverGroup.INSTANCE resolver.
So, when you create your WebClient bean, you can do the following
@Bean
@Primary
public WebClient webClient() {
HttpClient httpClient = HttpClient.create().resolver(DefaultAddressResolverGroup.INSTANCE);
return WebClient.builder()
.clientConnector(new ReactorClientHttpConnector(httpClient))
.build();
}
Explanation from the Netty documentation on why this works:
By default, the HttpClient uses Netty’s domain name lookup mechanism that resolves a domain name asynchronously. This is as an alternative of the JVM’s built-in blocking resolver.
Sometimes, you may want to switch to the JVM built-in resolver.
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Use can use " eureka.instance.prefer-ip-address=true " in application.properties file of all the microservices you are calling from api-gateway. Root cause is that your api-gateway is calling the microservices using username of the system which you need to call using ip address of the system.
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