See 662304. This should be in the troublshooting, or perhaps a note in the reserve workflow section. If you aren't seeing machines which you're sure should be displayed, check that the Distro name you are using is available on the lab controller where the system resides. Perhaps use a distro that is not so recent.
Patch available: http://gerrit.beaker-project.org/4500
To summarize discussion with rjoost... The patch for updating the docs doesn't seem like a good answer to me, I don't think anybody will ever find it if they are suffering this problem. Moreover the point of Reserve Workflow is to be the "easy" "one-click" solution which *shouldn't* require studying the docs in order to use it. A better solution would be to show a warning on the "reserve systems" grid (when browsing for a specific system) to tell you that the distro tree you have selected is not available in certain labs. The distro tree you have selected (RHEL-7.2 Server x86_64) is not available on the following lab controllers: * lab-02.rdu.example.com That should be enough of a hint for the user if they are confused as to why all the RDU systems are missing from the list (to take an arbitrary example).