Sometimes investigating what Juju is doing when things go wrong can be some what magical. As part of that process Juju offers the ability to introspect what is running internally via an engine report.
The engine report is a great big yaml of all the manifolds and workers that are currently known about. I hesitate to say active, because some might be stopped or not required.
The following tool, which I hope to embellish on as time goes by, is a tool to parse the engine report and give you back some very vital clues to what is happening at the time of the engine report collection. It will give meaningful feedback and pointers of where to look if a problem occurs.
You can grab it here https://github.com/SimonRichardson/juju-inspect