fix(canary): skip steps when in rollback window and rs is still active

Resolve argoproj#2939

rollout/canary.go

@@ -359,13 +359,18 @@ func (c *rolloutContext) syncRolloutStatusCanary() error {
 
 	if replicasetutil.PodTemplateOrStepsChanged(c.rollout, c.newRS) {
 		c.resetRolloutStatus(&newStatus)
-		if c.newRS != nil && c.rollout.Status.StableRS == replicasetutil.GetPodTemplateHash(c.newRS) {
-			if stepCount > 0 {
+		if c.newRS != nil && stepCount > 0 {
+			if c.rollout.Status.StableRS == replicasetutil.GetPodTemplateHash(c.newRS) {
 				// If we get here, we detected that we've moved back to the stable ReplicaSet
-				c.recorder.Eventf(c.rollout, record.EventOptions{EventReason: "SkipSteps"}, "Rollback to stable")
+				c.recorder.Eventf(c.rollout, record.EventOptions{EventReason: "SkipSteps"}, "Rollback to stable ReplicaSets")
+				newStatus.CurrentStepIndex = &stepCount
+			} else if c.isRollbackWithinWindow() && replicasetutil.IsActive(c.newRS) {
+				// Else if we get here we detected that we've moved back within the allowed window
+				c.recorder.Eventf(c.rollout, record.EventOptions{EventReason: "SkipSteps"}, "Rollback within window to active ReplicaSets")
 				newStatus.CurrentStepIndex = &stepCount
 			}
 		}
+
 		newStatus = c.calculateRolloutConditions(newStatus)
 		return c.persistRolloutStatus(&newStatus)
 	}

utils/replicaset/replicaset.go

@@ -341,6 +341,15 @@ func FindActiveOrLatest(newRS *appsv1.ReplicaSet, oldRSs []*appsv1.ReplicaSet) *
 	}
 }
 
+// IsActive returns if replica set is active (has, or at least ought to have pods).
+func IsActive(rs *appsv1.ReplicaSet) bool {
+	if rs == nil {
+		return false
+	}
+
+	return len(controller.FilterActiveReplicaSets([]*appsv1.ReplicaSet{rs})) > 0
+}
+
 // GetReplicaCountForReplicaSets returns the sum of Replicas of the given replica sets.
 func GetReplicaCountForReplicaSets(replicaSets []*appsv1.ReplicaSet) int32 {
 	totalReplicas := int32(0)