Part of https://discourse.jujucharms.com/t/read-before-contributing/47, an opinionated guide by William Reade
When you’re trying to get juju to do something new, you’ll need to write
code to cover a lot of responsibilities. Most of them are relatively
easy to discharge, but you still have to do something – not much will
happen by magic.
There’s a lengthy discussion of the layers and proto-layers that exist
in juju in the “Managing Complexity” doc in the wiki; this won’t cover
the exact same ground, so go and read that too.