Install:
sudo apt-get install erlang yaws
Edit /etc/yaws/conf.d/localhost.conf and /etc/yaws/conf.d/localhost-ssl.conf to configure the site(s).
In /etc/yaws/yaws.conf, you can specify the directory for additional beam files, by default it is:
ebin_dir = /usr/lib/yaws/custom/ebin
To start a module when yaws starts, use runmod, for example:
runmod = start_mongodb
Note that the module should have an exported function start/0.