kubernetes: kubectl stopped working after reboot

/kind bug

What happened: I’ve installed Kubernetes 1.9.2 on the master node (Ubuntu 16.04) including the dashboard. All the pods were running fine. But after rebooting, when I try to run kubectl get nodes or kubectl get pods I get:

The connection to the server 10.50.88.230:6443 was refused - did you specify the right host or port?

If I run kubectl cluster-info I get:

Kubernetes master is running at https://10.50.88.230:6443

To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
The connection to the server 10.50.88.230:6443 was refused - did you specify the right host or port?

But if I run kubectl cluster-info dump I get the same error.

What you expected to happen: See the list of nodes and work as usual

How to reproduce it (as minimally and precisely as possible): I’ve installed Kubernetes 1.9.2 on the master node (Ubuntu 16.04) including the dashboard and using Flannel as pod network. All seemed to run fine. Then I rebooted and I got that error.

Anything else we need to know?:

Environment:

• Kubernetes version (use kubectl version): 1.9.2

• Cloud provider or hardware configuration: CPU#/GHZ: 2, 1 GHz RAM: 16 GB

• OS (e.g. from /etc/os-release): NAME=“Ubuntu” VERSION=“16.04.3 LTS (Xenial Xerus)” ID=ubuntu ID_LIKE=debian PRETTY_NAME=“Ubuntu 16.04.3 LTS” VERSION_ID=“16.04” HOME_URL=“http://www.ubuntu.com/” SUPPORT_URL=“http://help.ubuntu.com/” BUG_REPORT_URL=“http://bugs.launchpad.net/ubuntu/” VERSION_CODENAME=xenial UBUNTU_CODENAME=xenial

• Kernel (e.g. uname -a): Linux ECS-9ce3f5ca 4.4.0-64-generic #85-Ubuntu SMP Mon Feb 20 11:50:30 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

• Install tools: Followed https://kubernetes.io/docs/setup/independent/install-kubeadm/

• Others: