Spring Boot API Gateway Unable to resolve name

Question

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]

Answer 1

Add this config to your microservice

eureka.instance.hostname=localhost

Answer 2

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.

Answer 3

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.