robotrain uses MQTT as the communication protocol between the train and connected devices like the remote-control. MQTT uses a publish/subscribe model to relay messages between clients. Clients can publish messages on topics, other clients can subscribe to those topics to receive the messages. The communication in the MQTT network is handled by the so-called MQTT broker, which manages the topics and relays the messages between clients that are publishing/subscribing to/from the same topic.
For a detailled description of this concept, please have a look into this post at hivemq.com.
This module come swith a broker you can use out of the box. At the end of this document there's notes on alternatives to this option.
Make sure that the machine your broker will be running on is available in the same network your robotrain and remote controls are connected to.
This module provides a Dockerfile that fires up a HiveMQ Community Edition instance.
Learn how to install Docker on your system.
If Docker is installed on your machine, you can build and start the container it with
$ docker build -t robotrain-mqtt-broker .
$ docker run -d -p 1883:1883 --name robotrain-mqtt-broker robotrain-mqtt-brokerThe MQTT broker will now be available at port 1883.
The container keeps running in the background until either you stop it or the system is being shut down. So for normal operation you don't need to touch it anymore. However, during development there's a couple of information you can get from the container that gives you insights into what's going on in your MQTT network.
As the container itself does not provide any output, you have to log into the running container and see what the broker is logging inside.
To log into the running container, issue this command:
$ docker exec -it robotrain-mqtt-broker /bin/shNow you're on a shell inside the container. It might not have the exact feature set you know from your computer's shell. I'll show you some commands, you cna figure out the rest.
NOTE: If you don't know how to display logfiles, have a look into this tutorial.
HiveMQ is creating a couple of different logfiles in the directory /log. You'll find a full description of the logging capabilities of HiveMQ in their documentation.
This gives you a quick overview of the most interesting logs:
/log/hivemq.log lists log messages of the broker itself. It shows you when it was started, which extensions where started and if you have issues in your configuration.
/log/events.log lists when a device was connected and disconnected and when a message was dropped. This is very useful information if you have communication issues with a device and want to find out what's going on.
Alternatively you can install the MQTT broker directly on your system, use a broker that's already running on your system or a publicly available one. I won't go in depth on that as every option has their pros and cons. Robotrain is only tested with the option described above.
In any case make sure that you configure remote-control and motor-control correctly so they can talk to this broker.