Small tool for discovering the rosmaster URI on a local network using dns-sd
Make sure avahi is running on your system to broadcast services (obtained on Ubuntu with apt package avahi-daemon) and copy rosmaster.service into /etc/avahi/services/. You can verify it's running with avahi-browse -a which should have an entry like below:
+ enp3s0 IPv4 rosmaster on <hostname> _ros._tcp local
You can store it in an environment variable like so:
export ROS_MASTER_URI=$(rosmaster-discovery)