feat: add support for degraded diff drift calculation (#209)

Author: michaelawyu

pkg/controllers/workapplier/apply.go

@@ -320,8 +320,12 @@ func (r *Reconciler) serverSideApply(
 		Resource(*gvr).Namespace(manifestObj.GetNamespace()).
 		Apply(ctx, manifestObj.GetName(), manifestObj, applyOpts)
 	if err != nil {
-		wrappedErr := controller.NewAPIServerError(false, err)
-		return nil, fmt.Errorf("failed to apply the manifest object: %w", wrappedErr)
+		// Note (chenyu1): the current implementation of NewAPIServerError flattens the passed-in error,
+		// effectively dropping the error hierarchy. This can be an issue if the caller of the function
+		// needs to identify a specific error in the hierarchy; to avoid this, this method will not return
+		// any error wrapped by NewAPIServerError.
+		_ = controller.NewAPIServerError(false, err)
+		return nil, fmt.Errorf("failed to apply the manifest object: an error is returned by the API server: %w", err)
 	}
 	return appliedObj, nil
 }

pkg/controllers/workapplier/controller.go

@@ -276,6 +276,7 @@ const (
 	ApplyOrReportDiffResTypeNotTakenOver                   ManifestProcessingApplyOrReportDiffResultType = "NotTakenOver"
 	ApplyOrReportDiffResTypeFailedToRunDriftDetection      ManifestProcessingApplyOrReportDiffResultType = "FailedToRunDriftDetection"
 	ApplyOrReportDiffResTypeFoundDrifts                    ManifestProcessingApplyOrReportDiffResultType = "FoundDrifts"
+	ApplyOrReportDiffResTypeFoundDriftsInDegradedMode      ManifestProcessingApplyOrReportDiffResultType = "FoundDriftsInDegradedMode"
 	// Note that the reason string below uses the same value as kept in the old work applier.
 	ApplyOrReportDiffResTypeFailedToApply ManifestProcessingApplyOrReportDiffResultType = "ManifestApplyFailed"
 
@@ -297,15 +298,17 @@ const (
 	ApplyOrReportDiffResTypeFailedToReportDiff ManifestProcessingApplyOrReportDiffResultType = "FailedToReportDiff"
 
 	// The result type for successful diff reportings.
-	ApplyOrReportDiffResTypeFoundDiff   ManifestProcessingApplyOrReportDiffResultType = "FoundDiff"
-	ApplyOrReportDiffResTypeNoDiffFound ManifestProcessingApplyOrReportDiffResultType = "NoDiffFound"
+	ApplyOrReportDiffResTypeFoundDiff               ManifestProcessingApplyOrReportDiffResultType = "FoundDiff"
+	ApplyOrReportDiffResTypeFoundDiffInDegradedMode ManifestProcessingApplyOrReportDiffResultType = "FoundDiffInDegradedMode"
+	ApplyOrReportDiffResTypeNoDiffFound             ManifestProcessingApplyOrReportDiffResultType = "NoDiffFound"
 )
 
 const (
 	// The descriptions for different diff reporting result types.
-	ApplyOrReportDiffResTypeFailedToReportDiffDescription = "Failed to report the diff between the hub cluster and the member cluster (error = %s)"
-	ApplyOrReportDiffResTypeNoDiffFoundDescription        = "No diff has been found between the hub cluster and the member cluster"
-	ApplyOrReportDiffResTypeFoundDiffDescription          = "Diff has been found between the hub cluster and the member cluster"
+	ApplyOrReportDiffResTypeFailedToReportDiffDescription      = "Failed to report the diff between the hub cluster and the member cluster (error = %s)"
+	ApplyOrReportDiffResTypeNoDiffFoundDescription             = "No diff has been found between the hub cluster and the member cluster"
+	ApplyOrReportDiffResTypeFoundDiffDescription               = "Diff has been found between the hub cluster and the member cluster"
+	ApplyOrReportDiffResTypeFoundDiffInDegradedModeDescription = "Diff has been found in degraded mode: cannot perform partial comparison as the member cluster API server rejected the manifest object (object is invalid)"
 )
 
 var (
@@ -319,6 +322,7 @@ var (
 		ApplyOrReportDiffResTypeNotTakenOver,
 		ApplyOrReportDiffResTypeFailedToRunDriftDetection,
 		ApplyOrReportDiffResTypeFoundDrifts,
+		ApplyOrReportDiffResTypeFoundDriftsInDegradedMode,
 		ApplyOrReportDiffResTypeFailedToApply,
 		ApplyOrReportDiffResTypeAppliedWithFailedDriftDetection,
 		ApplyOrReportDiffResTypeApplied,