Spring Boot API Gateway Unable to resolve name - spring-boot

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

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 2

Add this config to your microservice
eureka.instance.hostname=localhost

Answer 3

You 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.

Answer 4

Add this property in your property file:
eureka.instance.hostname=localhost

Answer 5

I have had the same problem, I was able solve it changing de version of spring. Here my POM.
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.3.9.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.demo.microservices</groupId>
<artifactId>api-gateway</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>api-gateway</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>11</java.version>
<spring-cloud.version>Hoxton.SR10</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-config</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-gateway</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>

Answer 6

Adding below property in API Gateway should address this. Its seems on windows platform discovery of the API gateway is not by default.
spring.cloud.discovery.enabled=true
Refer to the link below.
"https://stackoverflow.com/questions/65333590/spring-cloud-api-gateway-routing-not-working

Answer 7

I faced the same problem and found that this is because of the Spring and spring.cloud versions.
I have changed my pom.xml like below. In the parent I have commented 2.4.4 and used 2.2.6 and then in properties I have replaced the spring.cloud.version 2020.0.2 with
Hoxton.SR3 that's it then it started working.
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<!-- <version>2.4.4</version> -->
<version>2.2.6.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<properties>
<java.version>11</java.version>
<!-- <spring-cloud.version>2020.0.2</spring-cloud.version> -->
<spring-cloud.version>Hoxton.SR3</spring-cloud.version>
</properties>

Answer 8

I have resolved this issue by the another way.
For those who encountered this issue with Spring Webflux + Spring Cloud do the following:
You need to autowire DiscoveryClient discoveryClient;
add this method into your service layer (where you using WebClient):
private String getGatewayBaseUrl(ServiceInstance instance) {
return instance.getUri().toString();
}
Get the url of gateway from the instance
getGatewayBaseUrl(discoveryClient.getInstances("YOUR_GATEWAY_SERVICE_NAME").get(0)
Maybe this is not the best way to solve the problem, or maybe not the most correct one, but working