My nodes Digital Ocean are UNREACHABLE from docker cloud

Question

I have worked with docker cloud for a month. My nodes are created as described at https://docs.docker.com/docker-cloud/infrastructure/link-do/ for a Digital Ocean account. But I've decided to update the operating system of the node (I access through ssh):

$ sudo apt update && sudo apt upgrade 

Then increase the swap memory as described here: https://www.digitalocean.com/community/tutorials/how-to-add-swap-on-ubuntu-14-04

I finally reboot the system:

$ Sudo reboot 

But after this my system is already inaccessible from Docker cloud, status nodes is UNREACHABLE

When running

$ docker version 

I get:

    Docker version 
    Client: 
     Version: 1.11.2-cs5 
     API version: 1.23 
     Go version: go1.5.4 
     Git commit: d364ea1 
     Built: Tue Sep 13 15:26:43 2016 
     OS / Arch: linux / amd64 

Can not connect to the Docker daemon. Is the docker daemon running on this host?

How can I recover these nodes? I appreciate your help.