Reliable Server Client Communication in python

Question

Trying to create a reliable communication from server to client in python. the loss and delay of reception should be as low as possible. Here is my thought,

• client notices server(DNS) when internet is up
• server saves client IP
• broadcast data1 to saved IPs
• client ack msg idx to server
• server resend until client ack (with timeout)
• server removes IP if 3 broadcasts without ack

where data (json/df/db):

• data1: msg idx & broadcast msg
• data2: ip, last msg idx & connected timestamp

Now, just wanna make it simple but wish to be expandable. Is there any general practice of doing it? a backend(REST) may be necessary in future. I previously thought FCM notification might suit my need but seem not much python related resources to start up with. Please advise if the above idea is good enough.