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]

Conradconrade

how are you registering the clients? – Truscott

put "eureka.instance.prefer-ip-address=true" in application.properties of microservices to be fetched through gateway. I hope this helps. – Teddy

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.

Baseler

Answer 2

Add this config to your microservice

eureka.instance.hostname=localhost

Matos

Not working - #67381565 – Meatball

It was not working for me either. Then I realized I have to propagate eureka.instance.hostname=localhost to all microservices I wanted to access via the api-gateway. – Dabney

This fixed my issue... but could you explain why? – Facies

It also solved my problem. But, don't know how exactly it works. – Kensell

It's working when you add to your all microservices. – Matelote

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.

Twotime

lol... exactly after 2 years i faced this issue again and found my answer. – Twotime

Answer 4

Add this property in your property file:

eureka.instance.hostname=localhost

Paradis

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>

Evaluate

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://mcmap.net/q/669636/-spring-cloud-api-gateway-routing-not-working

Trioecious

This not working for Spring Cloud 2020.0.2 + Spring Webflux + Netty. The issue still ocurring – Hildebrand

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>

Bennett

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:

1. You need to autowire DiscoveryClient discoveryClient;
2. add this method into your service layer (where you using WebClient):

    private String getGatewayBaseUrl(ServiceInstance instance) {
        return instance.getUri().toString();
      }

3. 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

Hildebrand

Answer 9

This really disturbed me but I was able to find a solution that worked for me. I am using spring boot 3, Java 17 and CentOS 8. I had to edit the file /etc/hostname. Initially, it had cantos as a host. removed everything in that file and it worked for me. Hope this helps

Guadalquivir

Answer 10

add following configuration into application.properties

eureka.instance.hostname=localhost
eureka.instance.prefer-ip-address=true

1.eureka.instance.hostname=localhost:

Effect: This setting explicitly sets the hostname to localhost for the Eureka instance registration. Resolution: By using localhost, you ensure that all service registrations point to localhost, which is always resolvable in a local development environment.

2.eureka.instance.prefer-ip-address=true:

Effect: This setting tells Eureka to use the IP address of the instance instead of the hostname for registration and communication. Resolution: Using the IP address (127.0.0.1 for localhost) avoids DNS resolution issues, ensuring that services can communicate reliably.

The issue arose because Eureka was trying to register the services using a hostnam that couldn't be resolved. This is common in local development environments where hostnames may not be properly configured or resolvable.

Slavophile