VPN-based instance with LCM
In this tutorial, you are shown how to instantiate a workspace that is accessed over VPN and for which LCM provides messaging.
The instantiation process for this tutorial is entirely similar to that of the tutorial VPN-based instance with ROS and Brunel Hand through the end of the subsection Your first log-in in that tutorial. Note that the instructions here for passing LCM messages to and from your instance can be applied to any workspace type.
Building and installing LCM
This subsection provides instructions to install LCM in your fresh workspace instance. To get the latest official release, in the terminal that has an active SSH session, enter
curl -L -O https://github.com/lcm-proj/lcm/archive/v1.3.1.tar.gz shasum -a 256 v1.3.1.tar.gz
The last line of output should be
Checking the SHA-256 hash of the downloaded file provides confidence that the file has not been maliciously modified.
Assuming the base image used in the tutorial with ROS and Brunel Hand, two more packages must be installed:
apt-get -y install autoconf libglib2.0-dev
Now, build LCM from the source release as follows
tar -xzf v1.3.1.tar.gz cd lcm-1.3.1/ ./configure && make && make install
As a superficial check of the installation, try
which should print its version number. Now, finish configuring the instance host:
export LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH export LCM_DEFAULT_URL=udpm://22.214.171.124:7667?ttl=1 sudo route add -net 126.96.36.199 netmask 240.0.0.0 dev tap0
The last two lines are critical because they
- configure LCM to use
TTL=1, which causes multicast messages to be sent from the host into the network (up to one hop); and
- add a route that sends LCM multicast messages to the
tap0device, which corresponds to the VPN of the instance.
Example: listener and sender
For the example Python LCM listener,
cd /root/lcm-1.3.1/examples/python ./gen-types.sh
which will generate the message types that are used in this example. Now
Open a new terminal on your computer, i.e., the computer from which you are following this tutorial, not the one in the instance. Build LCM locally if you do not have it already. Then, configure routing for the LCM multicast subnet:
sudo route add -net 188.8.131.52 netmask 240.0.0.0 dev tap0
Finally, start to send LCM messages
export LCM_DEFAULT_URL=udpm://184.108.40.206:7667?ttl=1 python send-message.py
and a message should be printed from the listener.py program that is running within the instance.