Whereas 3-base-server installs critical packages needed by all, this 4th `stage <https://github.com/iiab/iiab/wiki/IIAB-Contributors-Guide#ansible>`_ installs a broad array of *options* — depending on which server apps will be installed in later stages — as specified in `/etc/iiab/local_vars.yml <http://FAQ.IIAB.IO#What_is_local_vars.yml_and_how_do_I_customize_it%3F>`_