It would be nice if there were a binary sensor indicating the connection state to the UniFi controller. Some times I need to reset my controller 
Curious about why your controller need reset.
Try SNMP component as sensor. Unifi has snmp. I haven’t used this.
Ever since I moved my controller to a docker container on my NAS box it sometimes drops out. I’d just like to see if the component’s connection is active. I haven’t been able to get much info on the SNMP support for UniFi but, not sure if this will completely cover my issue.
What docker image are you using.
Been running in docker 1yr without issue (5sites)
I created and use my own image since no official existed.
Let me know if you want dockerfile to try
I’ve been having issues with unifi device tracker component (HA server issue) and looking to use SNMP instead. In will find SNMP OID for status and post after I test.
I’ve been using this one
https://hub.docker.com/r/jacobalberty/unifi/
haven’t really been able to troubleshoot enough to call it a bug.