How to append an overlay bundle to a base bundle

Instead of providing overlays as external files, you may alternatively leverage Juju’s support for multi-document YAML files and provide both the base overlay and any required overlays as a single file.

To do so, the contents of each overlay can be appended after the base bundle contents using the special YAML document separator token --- as the delimiter. For example:

applications:
  mysql:
    charm: "cs:mysql-57"
    num_units: 1
    to: ["lxd:wordpress/0"]
--- # This is part of overlay 1
applications:
  mysql:
    num_units: 1
--- # This is part of overlay 2
applications:
  mysql:
    trust: true

When processing multi-document bundles, Juju will treat the first document as the base bundle and any subsequent document as an overlay.