feat: Add sync-dependencies

alexec commented 1 year ago

This PR introduces a new feature: sync dependencies.

Sync dependencies give a new way to order sync operations that is influenced by sync waves and sync hooks (all of which I wrote, so I know it extremely well).

Like sync waves, a sync operation will only progress when all the dependents have completed.

Dependencies between objects is specified by the new argocd.argoproj.io/sync-dependencies annotation.

# The dependencies are specified as a comma-separated list of objects.
# The format of each object is <group>/<kind>/<namespace>/<name>
# The group and kind are optional. If not specified, they'll match any group or kind.
# The namespace is optional. If not specified, the namespace is assumed to be the same as the namespace of the object.
# The name is required.
argocd.argoproj.io/sync-dependencies: a,b,c

Reasons to do this:

The 3rd most popular enhancement request for Argo CD
Explanation can be found in argo-cd#3517.
Implementation is contained within the GitOps engine.

Reasons not to do this:

Impacts core GitOps engine code (must be mitigated by exceptional testing).
Another gun to shoot yourself in the foot with.

Open questions:

Sync waves, hooks, and dependencies have a certain level of opacity to them. By which I mean, that it is not always clear what they're doing unless you're familiar with the app. I wonder if we should introduce a new "waiting" state for resources?
Should dependencies take precedence over waves? I think this is yes.
How should dependencies be described? I've used annotation, is that right? Is that the right structure?
Are the rules that match tasks to dependencies?

codecov[bot] commented 1 year ago

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (ed70eac) 55.75% compared to head (745fb5a) 55.61%. Report is 18 commits behind head on master.

:exclamation: Current head 745fb5a differs from pull request most recent head de3f8c9. Consider uploading reports for the commit de3f8c9 to get more accurate results

Files	Patch %	Lines
pkg/sync/sync_context.go	64.28%	4 Missing and 1 partial :warning:
pkg/sync/sync_tasks.go	94.73%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #514 +/- ## ========================================== - Coverage 55.75% 55.61% -0.15% ========================================== Files 41 42 +1 Lines 4525 4531 +6 ========================================== - Hits 2523 2520 -3 - Misses 1808 1817 +9 Partials 194 194 ```

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