public static boolean useJdkDnsResolver() {
        return USE_JDK_DNS_RESOLVER;
    }
Enables {@link DefaultAddressResolverGroup} that resolves domain name using JDK's built-in domain name
lookup mechanism.
Note that JDK's built-in resolver performs a blocking name lookup from the caller thread, and thus
this flag should be enabled only when the default asynchronous resolver does not work as expected,
for example by always throwing a {@link DnsNameResolverTimeoutException}.

<p>This flag is disabled by default.
Specify the {@code -Dcom.linecorp.armeria.useJdkDnsResolver=true} JVM option
to enable it.
core/src/main/java/com/linecorp/armeria/common/Flags.java