Same with this topic - Device is offline all the time
I even tried to restart resin-supervisor service with this command:
balena-engine restart <ID of resin-supervisor>
Any idea?
It’s online right now.
Maybe balena cloud server issue? 
Thanks for confirming that the device is back online. If the issue was indeed “Cannot resolve host address”, it’s usually an issue with “internet infrastructure”, i.e. name servers provided by the Internet Service Providers, which could be on the device’s local network, or indeed could also be in the cloud: Amazon Web Services. I am not aware of other users reporting name resolution issues in the past day or so, so I’d risk saying the issue was closer to the device’s local network. In any case, thanks for reporting it, let us know if it reoccurs or if we could be of further help.