Google’s PubSubHubbub (PuSH) - No that wasn't a typo
PubSubHubbub is a simple, open, server-to-server web-hook-based pubsub (publish/subscribe) protocol as an extension to Atom and RSS.
The theory is when a subscriber subscribes with the publisher’s feed, it subscribes to the publisher’s declared hub, and when the publisher has an update, it pings the hub to notify it there is something new, and then the hub can effectively pull the newly published feed and posts the update to the subscriber’s endpoint URL within a second.
This protocol makes instant updates possible for RSS, largely reduced the load of the publisher, and also avoids the subscriber repeat polling the URL. The protocol is decentralized and free. Anybody can run a hub, or anybody can ping (publish) or subscribe using open hubs like Google App Engine.
The drawback is the subscriber must have a known IP address, which means it can’t be behind the firewall or NAT. However, by using some kind of proxy, we can get an external IP address.
Currently, many CMSs have the plug-ins that support PubSubHubbub. For example, WordPress has the plugin named PuSHPress, which enables the updates to be sent directly from WordPress to you r PuSH subscribers. It is good to see that PubSubHubbub gets its popularity very soon.
