Improve NewPodControllerForExistingPod to set podReady to true (#…

…2623)

* Improve `NewPodControllerForExistingPod` to set `podReady` to true

`NewPodControllerForExistingPod` function was supposed to return the
podController for an existing pod. If this function is caleld, it would mean
that the pod is already runnign and we are creating `podController` for that
pod.
But this function didn't set `podReady` field of podController to true that
was beign checked in some other methods to make sure that the pod is running.
And because of that those methods would see the pod to be not running and
complain.
This commit fixes that by making sure that the pod is running and sets
`podReady` to true.

* Improve comment to function

pkg/kube/pod_controller.go

@@ -99,11 +99,20 @@ func NewPodController(cli kubernetes.Interface, options *PodOptions, opts ...Pod
 	return r
 }
 
-// NewPodControllerForExistingPod returns a new PodController given Kubernetes
-// Client and existing pod details.
-// Invocation of StartPod of returned PodController instance will fail, since the pod is already known.
-func NewPodControllerForExistingPod(cli kubernetes.Interface, pod *corev1.Pod) PodController {
-	r := &podController{
+// NewPodControllerForExistingPod returns a new PodController for the given
+// running pod.
+// Invocation of StartPod of returned PodController instance will fail, since
+// the pod is expected to be running already.
+// Note:
+// If the pod is not in the ready state, it will wait for up to
+// KANISTER_POD_READY_WAIT_TIMEOUT (15 minutes by default) until the pod becomes ready.
+func NewPodControllerForExistingPod(cli kubernetes.Interface, pod *corev1.Pod) (PodController, error) {
+	err := WaitForPodReady(context.Background(), cli, pod.Namespace, pod.Name)
+	if err != nil {
+		return nil, err
+	}
+
+	pc := &podController{
 		cli: cli,
 		pcp: &podControllerProcessor{
 			cli: cli,
@@ -117,9 +126,10 @@ func NewPodControllerForExistingPod(cli kubernetes.Interface, pod *corev1.Pod) P
 		Namespace:     pod.Namespace,
 		ContainerName: pod.Spec.Containers[0].Name,
 	}
-	r.podOptions = options
+	pc.podOptions = options
+	pc.podReady = true
 
-	return r
+	return pc, nil
 }
 
 func (p *podController) PodName() string {