wallaby inventory is a useful command for quickly checking up on the health of your pool and answering certain kinds of questions: Which nodes have checked in recently? Which nodes have checked in without being explicitly configured? Which nodes have never checked in?
Recently, I added constraint support to wallaby inventory. That is, instead of listing all nodes, you can choose to list only nodes for which a given Ruby expression is true. These constraints can be simple, like last_checkin < 1.hour_ago (which will find all nodes that have checked in more than one hour ago), or more complex. They are only limited by Ruby's