Why does my Java client fail to connect to ActiveMQ Artemis JMX when Artemis runs in a Docker container?

Below is some guidance on troubleshooting JMX connectivity when running ActiveMQ Artemis inside a Docker container:

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Key Points to Consider

• RMI Stub Advertisement
  The RMI mechanism used in JMX exports a stub that contains the server’s hostname (and sometimes an additional random port). When running inside a container, setting -Djava.rmi.server.hostname=localhost causes the stub to advertise “localhost” (which is local to the container) rather than an address reachable from outside. You need to set this property to the host’s accessible IP address or use a network configuration that makes the container’s networking visible externally.

• Port Mapping and Ephemeral Ports
  Even if you expose port 1099 for the registry, RMI often uses an additional dynamically assigned port for the actual connection. Ensure that the Docker run configuration maps all necessary ports. Alternatively, configure Artemis to use fixed ports for JMX communications so you can explicitly expose these ports.

• Using Docker’s Network Modes
  On Linux you might try using the host network (via --network=host) to reduce the network translation issues. On other platforms (e.g., macOS or Windows), you’ll need to use published ports and configure the advertised hostname correctly.

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What to Try Next

1. Set the Correct Hostname
   Instead of using localhost, set the java.rmi.server.hostname property (in your artemis.profile or other configuration) to the Docker host’s IP address. For example, if your host’s IP (reachable by the client) is 192.168.1.100, start Artemis with:

   SHELLCopied
   -Djava.rmi.server.hostname=192.168.1.100

2. Configure Fixed RMI Ports
   If possible, configure the JMX/RMI connector to use fixed ports for both the registry and the connection. This allows you to open and map those ports explicitly in your Docker configuration. Check Artemis documentation on how to force fixed ports for JMX connections.

3. Verify Port Mapping
   Make sure that in your Docker run command (or Docker Compose file) you expose not only port 1099 but also any additional port used by the RMI server stub. For example, in Docker Compose you might have:

   YAMLCopied
   ports:
     - "1099:1099"
     - "some_fixed_port:some_fixed_port"

   Replace some_fixed_port with the actual port used by the RMI connection if you can fix it.

4. Consider Host Networking (if applicable)
   On systems where host networking is available (such as Linux), running the container with the host network (--network=host) will let the container share the host’s network stack, alleviating issues with address translations.

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Summary

Your connection failure is likely due to the fact that the RMI stub, when created in a container, advertises an internal address (or a wrong hostname) and possibly an additional dynamic port that isn’t mapped. Adjusting the java.rmi.server.hostname to a resolvable IP and ensuring all necessary ports (or using host networking) should help resolve the issue.

These adjustments will allow your remote Java client to retrieve the RMIServer stub and establish the connection successfully.