RSSCloud is a new format specification for feeds that solves polling and notification issues. It works by adding a
cloud element to a feed which describes the path to a cloud server that should be notified when a feed is updated. The cloud server, in-turn, will send the updated feed content to all subscribers and aggregators. There is a description of this process on the RSSCloud website.
The protocol was designed by Dave Winer, who also drafted the original RSS specification and pioneered the use of feeds as a way to aggregate content. RSSCloud allows feeds to be more responsive and real-time. Rather than a polling model (‘are we there yet, are we there yet’), it pushes updates and update notifications down to subscribers via a cloud server and API.
The new protocol took a big step forward today as WordPress .com enabled the cloud tag on all post feeds (comment feeds will be enabled at some later point). Winer tweeted about it today, and Automattic’s Matt Mullenweg has since confirmed in an email that all WordPress.com blog feeds now support the tag. If you view the source of a feed on WordPress, such as this one, you can see the new tag:
<cloud domain='rsscloud.wordpress.com' port='80' path='/?rsscloud=notify' registerProcedure='' protocol='http-post' />
A cloud notification server is defined for each
channel in the feed. This now means that client tools that support the new protocol will be pushed updates whenever there is a new post on a WordPress.com blog that the user has subscribed to.
This could also mean the beginning of a new format war for the real-time web, reminiscent of the old RSS vs Atom battles. Another groups of developers, lead by Brad Fitzpatrick, published a format and cloud hub known as pubsubhubbub, which is now being supported by Google Reader. There is sure to be much discussion of WordPress.com falling into the RSSCloud camp, and which protocol/format/method etc. is better than the other (a debate we will engage in on this blog, no doubt).
Services such as Twitter and Friendfeed centralize real-time data and updates. RSSCloud and broader support of such a protocol is a step in the direction of decentralizing such services.
Update: The WordPress.com blog now has a post about the update