implement listener on each client

[caver456]

whether by websockets or by http polling or long polling or some combination - this will be needed in order to implement true multi-node behavior. For example, for the sign-in app, clients sync whenever the user taps any button, because there is plenty of time to do so because user interaction is normally slow enough and it's not urgent to see the synced data. By contrast, here, the latest data needs to be shown - and alerts raised - with no user interaction required to trigger the sync.

[caver456]

long polling is not a good option since each client will hog the connection, meaning you could only have one client on pythonanywhere, per https://www.pythonanywhere.com/forums/topic/27219/

will pursue websockets