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 $SAFE execution: among other things, they cannot modify running classes, perform file I/O, fork new processes, or, because of how QMF is implemented, invoke QMF methods on the node object. However, every QMF property of the node object is available to wallaby inventory constraints. The transcript below provides some examples running against a wallaby agent loaded up with test data.

(Cross-posted from Chapeau.)