fix(applicationset): ApplicationSets with rolling sync stuck in Pending

[Fsero]

In issue #19535 we have discovered a bug where ApplicationSet Progressive Sync feature gets stuck and it never recovers and get stuck forever unless you manually delete the existing applicationsStatus of the ApplicationSet affected or trigger a manual sync.

When the ApplicationSet is performing a progressive sync, the apps in the step being synced get the status Pending in the ApplicationSet applicationStatus . This means that the apps are gonna be synced and is waiting for the sync to start progressing.

Let's set an example, applicationset generates 3 applications. In the initial moment applicationset points to commit A

applicationset will generate those 3 applications and start the progressive sync, then application 2 is in Pending status, the applicationset status for application 2 is marked to targetrevision for app2 to A

At this moment in time applicationset gets updated to point to commit B, since app2 is in pending state the progressive sync allows it to the app to be synced and hence the app2 is synced to commit B

since applicationset targetrevision for app2 expects to be A but it's B will never move app2 from 'Pending' to 'Progressing' state.

Here is the logic that performs this check.

This new check was introduced in ArgoCD 2.12 causing this bug when a progressive sync is already being performed.

• Because first it will get the applicationStatus from the existing applicationStatus which is the one that has the old revision
• And since the app inside the ApplicationSet applicationStatus is in "Pending" the revision is never updated when it enters the if statement (see how currentAppStatus.TargetRevision never will be updated)

This means that the ApplicationSet will always think that the app is not being synced to the latest version and never progress, but in reality the app is actually in a later version but tha ApplicationSet never updated it in the apps that are in "Pending".

• This PR fixes this bug changing the logic that checks when an applications needs to be moved from Pending to Progressing, instead of rely on the targetrevision we actually rely just in the application being synced to move it. This also don't introduce a prior bug where it was cheched that the application was synced in a certain moment in time to ensure it was triggered by the applicationset controller.

• Note that if someone manually sync one application of the applicationset while it's being progresively synced after merging this PR the applciationset controller will continue the rollout

• Ensure that a certain revision is applied orderly in all applications generated from the applicationset it's certainly possible that a given application can be synced in a different revision than the one explicitly set in the appset

Fixes: #19535

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[crenshaw-dev]

@wmgroot thoughts on this?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.12%. Comparing base (e2bc96b) to head (3b62869).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #20230      +/-   ##
==========================================
- Coverage   55.17%   55.12%   -0.05%     
==========================================
  Files         324      324              
  Lines       55257    55249       -8     
==========================================
- Hits        30489    30457      -32     
- Misses      22142    22173      +31     
+ Partials     2626     2619       -7     

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[Fsero]

Came here to report that we are running this in production since 2 weeks ago and it fixed our issues syncing applicationsets when the conditions explained happened

[Fsero]

anyone else than @wmgroot can take a look?

[crenshaw-dev]

I've chatted w/ some folks at Red Hat. They're interested in moving Progressive Syncs from alpha to beta, so there's a chance they'll be able to put some time into reviews of progressive syncs bugs soon.