This is copied from the Flexhub site. I do not know if this is actually implemented by anyone.
Based on it’s ADC counterpart, the FO extension, I suggest implementing failover addresses for NMDC too.
This will provide the client with one or more alternative addresses (another hub, or a network array) to connect to in case the hub becomes unavailable for whatever reason (server crash, ISP trouble, DDOS etc).
The client could keep polling the original hubaddress to see if it’s back online again and take action based on client settings.
Example of a part of the client-hub login:
Client: $Supports … FailOver|
Hub: $Supports … FailOver|
Hub: $FailOver someaddress.no-ip.org,adc://someotheraddress.com:5432|
The $FailOver command can be sent by the hub at any time, after the $Supports reply from the hub, overwriting/replacing addresses of any previous $FailOver commands. An empty $FailOver command will clear the addresses and simply keep waiting for the hub to get back online: $FailOver|