Kubelet should keep the original PodStatus.Host when posting the status

[yujuhong]

I am seeing pod status update failures due to empty Host field. This prevents the pod status from being updated in some cases. Kubelet should always keep the original host.

[yujuhong]

In the case I saw, all containers of that pod has exited with 1, and the restart policy was never. There seems to be two issues.

1. kubelet queried docker and couldn't find the containers: "No pod infra container exists for this pod"
2. kubelet decided to return a pending status with no host set

(2) triggered a status update which attempted to clear the host field. This should not be allowed.

[yujuhong]

#6127 is a quick fix for 2. There is a broader question about whether "pending" is the best status to return in this case.

Whey kubelet won't report failed (1) still needs more investigation.

[bgrant0607]

I'd be happy if PodStatus.Host were eliminated from v1beta3 and just populated from PodSpec in v1beta1/2.

[yujuhong]

@bgrant0607, yes, I thought someone was working on that. Filed a issue just in case #6165.