Remotely Launch Nodes in ROS2

edit

As far as I can tell, this is still a work in progress, but has been on the backlog to get merged into the documentation. Lots of discussion here, and it seems the change to the documentation is awaiting approval to get merged in.

The tentative document can be found here, but it doesn't look like the proposed changes have made their way into code yet.

I'd imagine it is pretty low priority because ssh is possible on all the tier 1 platforms (ever since Windows joined the club).

My answer to this is to use the existing linux system to do this: systemd. Basically do the following:

On the target machine, the machine you want to run remote nodes on, do the following:

1. Make sure the nodes you want to run are on the remote machine already and it's already built on that machine.
2. Make a bash script that executes ros2 launch and sources the right install directory. We'll call this remote_ros.sh. This is a script because you might want to do other things with this.
3. Make a remote_ros.service file that runs the remote_ros.sh script. This can be setup to start on boot or not.

On the local machine, the machine you want to launch remote nodes on, do the following:

1. Make a launch script that SSHes into the remote machine and executes systemctl stop remote_ros and/or systemctl start remote_ros. This can be done with the ExecuteProcess launch action.

Stop will kill the nodes and start will bring them up. If you don't want to stop the nodes, I believe start is a NOOP if they are already running.

I think this solution is more straight forward than the others presented and ideally the service just runs all the time, but you can always kill it with the systemctl stop command.

I have found a solution that works for me be using rosbridge to remotely publish service messages to start or stop processes.

1. First I made rosbridge and a ros2 node start on boot of the device by:

sudo vim /etc/systemd/system/ros2node.service

[Unit]
Description=Start ROS2 Node
After=network.target

[Service]
ExecStart=/bin/bash -c 'source /opt/ros/humble/setup.bash; source 
/home/ketill/Documents/ros2_script/ros2_ws/install/setup.bash; ros2 launch rosbridge_server 
rosbridge_websocket_launch.xml; ros2 run node_starter talker'
User=ketill
Environment="DISPLAY=:0"
Environment="XAUTHORITY=/run/user/1000/gdm/Xauthority"
Restart=always

[Install]
WantedBy=multi-user.target

sudo systemctl enable ros2node.service sudo systemctl start ros2node.service

and similar for the node. 2. The a node for handling the processes depending on the service message for the gui

class NavigationService(Node):

def __init__(self):
    super().__init__('navigation_service')
    self.srv = self.create_service(SetBool, 'start_navigation', self.handle_service)
    self.process = None
    self.hasStartedOnce = False

def handle_service(self, request, response):
    response.success = self.run_navigation_launch_file(request.data)
    response.message = 'Navigation launch started.' if response.success else 'Failed to start navigation launch.'
    return response

def run_navigation_launch_file(self, start):
    if start and not self.hasStartedOnce:
        command = "source /opt/ros/humble/setup.bash; source /home/ggeo/auto_gpr/install/setup.bash; ros2 launch auto_gpr bringup.launch.py"
        self.process = subprocess.Popen(command, shell=True, executable="/bin/bash", preexec_fn=os.setsid)
        self.hasStartedOnce = True
        return self.process.poll() is None  # return True if process is running
    else:
        # Implement logic to stop the process here
        if self.process is not None:
            os.killpg(os.getpgid(self.process.pid), signal.SIGINT)  # Send the signal to all the process in the group
            self.process = None
            self.hasStartedOnce = False
        return False


def main(args=None):
    rclpy.init(args=args)

navigation_service = NavigationService()

rclpy.spin(navigation_service)

navigation_service.destroy_node()
rclpy.shutdown()


if __name__ == '__main__':
main()

This solution make it possible to start remotely as long as the devices are on the same network.