PubSubHubbub/WebSub (the latter is effectively the slightly modernized W3C standardization of the former) is the standard solution for that. (Feed declares wher

PubSubHubbub/WebSub (the latter is effectively the slightly modernized W3C standardization of the former) is the standard solution for that. (Feed declares where to register for updates (hubs), readers register their callback URLs with hubs, publishers tell hubs when something changed, hubs run through the registered callbacks and ping them with the update. Thus needs a server-component for the reader side.)