Error occurred running Grails CLI: Unknown Host (504) - grails

Question

I got an error Unknown Host (504) when I tried to start grails 3.3.2, and the details shows below:
$ grails --stacktrace --verbose
| Error Error occurred running Grails CLI: Unknown Host (504)
org.apache.http.client.HttpResponseException: Unknown Host (504)
at org.eclipse.aether.transport.http.HttpTransporter.handleStatus(HttpTransporter.java:466)
at org.eclipse.aether.transport.http.HttpTransporter.execute(HttpTransporter.java:291)
at org.eclipse.aether.transport.http.HttpTransporter.implPeek(HttpTransporter.java:231)
at org.eclipse.aether.spi.connector.transport.AbstractTransporter.peek(AbstractTransporter.java:43)
at org.eclipse.aether.connector.basic.BasicRepositoryConnector$PeekTaskRunner.runTask(BasicRepositoryConnector.java:376)
at org.eclipse.aether.connector.basic.BasicRepositoryConnector$TaskRunner.run(BasicRepositoryConnector.java:350)
at org.eclipse.aether.util.concurrency.RunnableErrorForwarder$1.run(RunnableErrorForwarder.java:67)
at org.eclipse.aether.connector.basic.BasicRepositoryConnector$DirectExecutor.execute(BasicRepositoryConnector.java:581)
at org.eclipse.aether.connector.basic.BasicRepositoryConnector.get(BasicRepositoryConnector.java:249)
at org.eclipse.aether.internal.impl.DefaultArtifactResolver.performDownloads(DefaultArtifactResolver.java:520)
at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:421)
at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolveArtifacts(DefaultArtifactResolver.java:246)
at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolveArtifact(DefaultArtifactResolver.java:223)
at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom(DefaultArtifactDescriptorReader.java:320)
at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.readArtifactDescriptor(DefaultArtifactDescriptorReader.java:217)
at org.eclipse.aether.internal.impl.DefaultDependencyCollector.resolveCachedArtifactDescriptor(DefaultDependencyCollector.java:535)
at org.eclipse.aether.internal.impl.DefaultDependencyCollector.getArtifactDescriptorResult(DefaultDependencyCollector.java:519)
at org.eclipse.aether.internal.impl.DefaultDependencyCollector.processDependency(DefaultDependencyCollector.java:409)
at org.eclipse.aether.internal.impl.DefaultDependencyCollector.processDependency(DefaultDependencyCollector.java:363)
at org.eclipse.aether.internal.impl.DefaultDependencyCollector.process(DefaultDependencyCollector.java:351)
at org.eclipse.aether.internal.impl.DefaultDependencyCollector.collectDependencies(DefaultDependencyCollector.java:254)
at org.eclipse.aether.internal.impl.DefaultRepositorySystem.resolveDependencies(DefaultRepositorySystem.java:341)
at org.springframework.boot.cli.compiler.grape.AetherGrapeEngine.resolve(AetherGrapeEngine.java:319)
at org.springframework.boot.cli.compiler.grape.AetherGrapeEngine.resolve(AetherGrapeEngine.java:301)
at org.springframework.boot.cli.compiler.grape.AetherGrapeEngine.resolve(AetherGrapeEngine.java:293)
at org.grails.cli.boot.GrailsDependencyVersions.<init>(GrailsDependencyVersions.groovy:53)
at org.grails.cli.boot.GrailsDependencyVersions.<init>(GrailsDependencyVersions.groovy:49)
at org.grails.cli.profile.repository.MavenProfileRepository.<init>(MavenProfileRepository.groovy:53)
at org.grails.cli.GrailsCli.createMavenProfileRepository(GrailsCli.groovy:334)
at org.grails.cli.GrailsCli.execute(GrailsCli.groovy:235)
at org.grails.cli.GrailsCli.main(GrailsCli.groovy:159)
| Error Error occurred running Grails CLI: Unknown Host (504)
Here is my version info:
$ grails -v
| Grails Version: 3.3.2
| Groovy Version: 2.4.13
| JVM Version: 1.8.0_121
Extra info: I am running it on Mac behind a proxy network. I've added the following statement into my bin/grails (/Users/foouser/.sdkman/candidates/grails/current/bin/grails) script:
export GRAILS_OPTS="-Dhttp.proxyHost=myHttpProxy -Dhttp.proxyPort=8000 -Dhttps.proxyHost=myHttpsProxy -Dhttps.proxyPort=443"

Answer 1

After few trials and errors, I found this org.eclipse.aether.internal.impl.DefaultRepositorySystem is actually trying to read and parse my $HOME/.m2/settings.xml. And below it was my original settings.xml:
<settings xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.1.0 http://maven.apache.org/xsd/settings-1.1.0.xsd"
xmlns="http://maven.apache.org/SETTINGS/1.1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<proxies>
<proxy>
<id>proxy</id>
<active>true</active>
<protocol>http</protocol>
<host>myHttpProxy</host>
<port>8000</port>
</proxy>
<proxy>
<id>httpsproxy</id>
<active>true</active>
<protocol>https</protocol>
<host>myHttpProxy</host>
<port>443</port>
</proxy>
</proxies>
<servers>
<server>
<username>myname</username>
<password>mypassword</password>
<id>Artifactory</id>
</server>
</servers>
<mirrors>
<mirror>
<id>Artifactory</id>
<!-- Drive all repositories through the Artifactory mirror -->
<mirrorOf>*</mirrorOf>
<url>http://myartifactoryurl</url>
</mirror>
</mirrors>
</settings>
Unfortunately, it wasn't parsed well...
The current workaround (a bad one though) I have is to change this settings.xml to the default one from maven, which has nothing setup there.