I'm trying to upgrade a Kubernetes multi-master cluster from v1.8.5 to v1.9.1 on Ubuntu 1604 LTS.
When I run
sudo kubeadm upgrade apply v1.9.1 it gets as far as backing up the old manifest for
kube-apiserver.yaml and then displays this:
[upgrade/staticpods] Waiting for the kubelet to restart the component
It then waits for 60 seconds (apparently a hard-coded time-out in kubeadm) before restoring the original state.
There's nothing obvious in the logs. What could be the issue?