UnknowhHostException using spring-cloud-starter-gateway with spring boot 2.4.0 and above - spring

Question

Related to https://github.com/reactor/reactor-netty/issues/1431.
Spring cloud gateway server starts correctly but requests via the gateway fail with the below exception:
java.net.UnknownHostException: failed to resolve 'myserver' after 4 queries
at io.netty.resolver.dns.DnsResolveContext.finishResolve(DnsResolveContext.java:1013)
Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException:
Error has been observed at the following site(s):
|_ checkpoint ? org.springframework.cloud.gateway.filter.WeightCalculatorWebFilter [DefaultWebFilterChain]
|_ checkpoint ? org.springframework.cloud.sleuth.instrument.web.TraceWebFilter [DefaultWebFilterChain]
|_ checkpoint ? org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter [DefaultWebFilterChain]
|_ checkpoint ? HTTP GET "/service/api/applications/123" [ExceptionHandlingWebHandler]
Stack trace:
at io.netty.resolver.dns.DnsResolveContext.finishResolve(DnsResolveContext.java:1013)
at io.netty.resolver.dns.DnsResolveContext.tryToFinishResolve(DnsResolveContext.java:966)
at io.netty.resolver.dns.DnsResolveContext.query(DnsResolveContext.java:414)
at io.netty.resolver.dns.DnsResolveContext.onResponse(DnsResolveContext.java:601)
at io.netty.resolver.dns.DnsResolveContext.access$400(DnsResolveContext.java:63)
at io.netty.resolver.dns.DnsResolveContext$2.operationComplete(DnsResolveContext.java:458)
.....
Works correctly when downgrading spring boot.

Answer 1

Fixed by adding the below bean definition:
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import io.netty.resolver.DefaultAddressResolverGroup;
import reactor.netty.http.client.HttpClient;
#Configuration
public class TempFixConfig {
#Bean
public HttpClient webClient() {
return HttpClient.create().resolver(DefaultAddressResolverGroup.INSTANCE);
}
}

Answer 2

If you don't want to change the logic of how the HttpClient bean is created, you can add a HttpClientCustomizer:
import org.springframework.cloud.gateway.config.HttpClientCustomizer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import io.netty.resolver.DefaultAddressResolverGroup;
import reactor.netty.http.client.HttpClient;
#Configuration
public class HttpClientResolverFixConfig {
#Bean
public HttpClientCustomizer httpClientResolverCustomizer() {
return new HttpClientCustomizer() {
#Override
public HttpClient customize(HttpClient httpClient) {
return httpClient.resolver(DefaultAddressResolverGroup.INSTANCE);
}
};
}
}