diff-bundle generates 2,000 lines of diffs even with an exported bundle

Could we confirm this is still hitting in 2.9.38?

It may be that there is an issue with default values for config attributes. Taking a few examples:

applications:
  barbican:
    options:
      action-managed-upgrade:
        bundle: null
        model: false

That says that the bundle does not define the 'action-managed-upgrade' value, but the model does have a value for it, and that value is 'false'.

Similarly for:
      max-allowed-request-size:
        bundle: null
        model: 25000

max-allowed-request-size is 25,000 in the model, but there is no value in the bundle.

My guess is that the model values are from defaults in the charm. But it does seem like 'diff-bundle' should be taking that sort of thing into account. Either export-bundle should be including the current values, or diff-bundle should be understanding default values.

> My guess is that the model values are from defaults in the charm. But it does seem like 'diff-bundle' should be taking that sort of thing into account. Either export-bundle should be including the current values, or diff-bundle should be understanding default values.

You are right. Most of the diff can be explained by that except for some relation stuff.

`juju export-bundle` already has --include-charm-defaults option so that could be used to mitigate the lines of diff, but diff-bundle could take advantage of source=default information in the model.

[juju config barbican]
====
settings:
  action-managed-upgrade:
    default: false
    description: |
    ...
    source: default
    type: boolean
    value: false
====

$ juju export-bundle > exported.yaml
$ juju diff-bundle ./exported.yaml | wc -l
2187

$ juju export-bundle --include-charm-defaults > exported_with_defaults.yaml
$ juju diff-bundle ./exported_with_defaults.yaml | tee diff_with_defaults.txt | wc -l
659

It's better with --include-charm-defaults. But there are some like:

====
applications:
  barbican:
    options:
      hmac-key-length:
        bundle: 32
        model: 32
====
-> value is the same but maybe the types are different (int vs string?)

and unnecessary diff in relations:

  - - barbican-mysql-router:shared-db
    - barbican:shared-db

vs

  - - barbican:shared-db
    - barbican-mysql-router:shared-db

Confirmed this still happens in 3.1.1, also this may be a duplicate of Bug #1842363

We frequently want to use diff-bundle in Support and always run into this issue. It would be great if we could prioritise a fix for this.