PI's DNS got wedged after physical power failure / restore.

[anschweitzer]

My pi’s dns got wedged after power loss / restore in Cambridge. Restart PI fixed it. I didn’t try restarting the router. Ideally we can figure out something less drastic, but if we can’t restore comm long enough, we should probably reboot the pi.

[anschweitzer]

I think this is same issue as #155, though that one documents some other issues.

[anschweitzer]

An approach:

1. We can detect DNS not working by the specific network error, and/or we can issue a ping to some well known server. As a backstop we detect by no mqtt broker connection after a long time.
2. Do some research into what service needed to be restarted and try to just restart that service.
3. If all else fails after a long time, reboot the pi.

[anschweitzer]

Probably same issue happened in Freedom on apple: log.zip

One of the errors:

 /home/pi/gw-scada-spaceheat-python/gw_spaceheat/proactor/mqtt.py, line 89, in _client_thread

 self._client.connect(self._client_config.host, port=self._client_config.port)
    File                              
 /home/pi/.local/lib/python3.10/site-packages/paho/mqtt/client.py, line 914, in connect
      return             
 self.reconnect()
    File /home/pi/.local/lib/python3.10/site-packages/paho/mqtt/client.py, line 1044, in       
 reconnect
      sock = self._create_socket_connection()
    File                                                   
 /home/pi/.local/lib/python3.10/site-packages/paho/mqtt/client.py, line 3685, in _create_socket_connection

 return socket.create_connection(addr, timeout=self._connect_timeout, source_address=source)
    File                
 /usr/local/lib/python3.10/socket.py, line 824, in create_connection
      for res in getaddrinfo(host, port, 0, 
 SOCK_STREAM):
    File /usr/local/lib/python3.10/socket.py, line 955, in getaddrinfo
      for res in          
 _socket.getaddrinfo(host, port, family, type, proto, flags):
  socket.gaierror: [Errno -3] Temporary failure in     
 name resolution

[anschweitzer]

We might be able to reproduce this simply by disconnecting ethernet for an hour.

Various flavors of this did not succeed in getting dns to work.

[anschweitzer]

Another work around is to record the IP on each successful DNS connection and use that if DNS appears to fail.