ROS over Multiple Machines

This manual explains the process for connecting ROS Nodes on multiple machines connected to the same network.

Example case for 2 Computers on same network:

Hostname	comp1	comp2
IP	192.168.77.11	192.168.77.12

Case 1: Using On-board ROS :-

• Configuring ROS master: There should be only a single master/ROS core for handling the system. In this example, let the comp1 be the master. Hence, roscore is run on this computer.

  comp1: $ roscore

• This should start the roscore displaying the master's IP address and the port number. 11311 is the default port of the master.

• Configuring Slaves:

  • The slave machines need to know the master's as well as their own IP address.

  • comp1 can act as a slave to itself along with being the master.

    Specify ROS master's IP:
    comp1: $ export ROS_MASTER_URI=http://192.168.77.11:11311

    Specify slave machine's own IP:
    comp1: $ export ROS_IP=192.168.77.11

  • comp2 will only act as a slave machine.

    Specify ROS master's IP:
    comp2 : export ROS_MASTER_URI=http://192.168.77.11:11311

    Specify slave machine's own IP:
    comp2 : $ export ROS_IP=192.168.77.12

  Note: In case of more number of machines, one of them can solely act as the master with the roscore running on it and all other nodes running on the slaves.

• Resolve master's name to IP (Optional):

  Modify the /etc/hosts file in order to resolve master's name to IP in the slave machine.

  • In the slave machine, comp2, open the file as Root user: comp2 : $ sudo nano /etc/hosts

  • Add the line to the hosts file in the format of:

    <Master's IP Address>    <Master's Name>

    For example,

    192.168.77.11             comp1

  • Save and close the file.

Note: The commands for specifying the IP address of ROS master and the slave can also be added to a bash file and sourced when required instead of typing it every time.

Case 2: Using MATLAB-ROS:

Robotics System Toolbox enables one to interface with ROS and use ROS functionality in MATLAB and Simulink. One can connect to a ROS network, collect data, send and receive one's own messages, and deploy code to a standalone system.

• Configuring ROS Master:

  • To initialize ROS master using MATLAB-ROS, run the following command in the MATLAB Command Window:

    For comp1,
    >> rosinit

  • This should start the roscore and display the IP address of ROS master and the port numbers of ROS Master and the global node on the command window.

  Note: For running a ROS node in the master, the MATLAB code just needs to be run. No separate configurations are required.

• Configuring Slaves:

  • Before running the slave nodes, MATLAB-ROS must be initialized with a master in the network. To do so, the IP address of the ROS master must be passed as an argument to the rosinit function.

    Eg: rosinit('<Master's IP Address>')

    For comp2,
    >> rosinit('192.168.77.11')

Note: In case of one of the computer with MATLAB-ROS and other with On-Board ROS, the nodes can communicate over the network using the corresponding configurations.