I recently created an Ubuntu 18.04 on Azure to run a test service I work on in my spare time and noticed that the
/etc/rc.local file doesn't exist by default anymore. There are other (probably preferred) ways to start applications when the server boots by rc.local was in my opinion, the absolute easiest.
etc/rc.local still works, you just have to create it and then give it execute permissions. Remember that it is a shell script so it will need to be setup as one.
# Always leave this line here
Permission required for /etc/rc.local
sudo chmod 755 /etc/rc.local