Wait for at least 1 replica for Deployments and Daemonsets

The wait logic for Deployments and Daemonsets subtracts their
maxUnavailable value from the amount of replicas they should
have ready. This can lead to waiting for 0 pods to be ready.
This change ensures at least 1 replica is ready, unless there
are 0 desired replicas.

Fixes #8660.

This is based on https://github.com/helm/helm/pull/8671 by
Sean Eagan which was never merged.

Co-authored-by: Sean Eagan <seaneagan1@gmail.com>
Signed-off-by: Sean Eagan <seaneagan1@gmail.com>
Signed-off-by: Chris Friesen <chris.friesen@windriver.com>

pkg/kube/ready.go

@@ -272,7 +272,17 @@ func (c *ReadyChecker) volumeReady(v *corev1.PersistentVolumeClaim) bool {
 }
 
 func (c *ReadyChecker) deploymentReady(rs *appsv1.ReplicaSet, dep *appsv1.Deployment) bool {
+	// If there are no desired replicas, there will be nothing to wait for.
+	if *dep.Spec.Replicas == 0 {
+		return true
+	}
+
+	// Ensure the expected available replicas are ready.
 	expectedReady := *dep.Spec.Replicas - deploymentutil.MaxUnavailable(*dep)
+	// Also ensure at least 1 replica is ready.
+	if expectedReady < 1 {
+		expectedReady = 1
+	}
 	if !(rs.Status.ReadyReplicas >= expectedReady) {
 		c.log("Deployment is not ready: %s/%s. %d out of %d expected pods are ready", dep.Namespace, dep.Name, rs.Status.ReadyReplicas, expectedReady)
 		return false
@@ -286,11 +296,18 @@ func (c *ReadyChecker) daemonSetReady(ds *appsv1.DaemonSet) bool {
 		return true
 	}
 
+	// If there are no desired replicas, there will be nothing to wait for.
+	if ds.Status.DesiredNumberScheduled == 0 {
+		return true
+	}
+
 	// Make sure all the updated pods have been scheduled
 	if ds.Status.UpdatedNumberScheduled != ds.Status.DesiredNumberScheduled {
 		c.log("DaemonSet is not ready: %s/%s. %d out of %d expected pods have been scheduled", ds.Namespace, ds.Name, ds.Status.UpdatedNumberScheduled, ds.Status.DesiredNumberScheduled)
 		return false
 	}
+
+	// Ensure the expected available replicas are ready.
 	maxUnavailable, err := intstr.GetValueFromIntOrPercent(ds.Spec.UpdateStrategy.RollingUpdate.MaxUnavailable, int(ds.Status.DesiredNumberScheduled), true)
 	if err != nil {
 		// If for some reason the value is invalid, set max unavailable to the
@@ -298,8 +315,11 @@ func (c *ReadyChecker) daemonSetReady(ds *appsv1.DaemonSet) bool {
 		// `MaxUnavailable` function in deploymentutil
 		maxUnavailable = int(ds.Status.DesiredNumberScheduled)
 	}
-
 	expectedReady := int(ds.Status.DesiredNumberScheduled) - maxUnavailable
+	// Also ensure at least 1 replica is ready.
+	if expectedReady < 1 {
+		expectedReady = 1
+	}
 	if !(int(ds.Status.NumberReady) >= expectedReady) {
 		c.log("DaemonSet is not ready: %s/%s. %d out of %d expected pods are ready", ds.Namespace, ds.Name, ds.Status.NumberReady, expectedReady)
 		return false