This is a higher level app on top of the core rpm-ostree tool. It
contains a variety of tools and scripts for making disk images, the
"repoweb" generator, and such.
The "postprocess" command is still useful though as a way to avoid creating multiple disk images for different variants.
The "trivial-autobuilder" code is also being reworked into new scripts in fedora-atomic.
Most likely, you want to start using rpm-ostree by running a "compose" server. We use the term "compose" instead of "build" as there's no actual source code being changed here, just a mechanical transformation of RPM -> OSTree -> disk images.
First, you need to run through the setup instructions of the current rpm-ostree README.md.
Once you've done this, see doc/autobuilder.json for a sample JSON
configuration file for the autobuilder.
$ rpm-ostree-toolbox trivial-autocompose /path/to/autobuilder.json