Requests for comment/Publishing the RecentChanges feed

RCStream

MediaWiki supports (as of v1.22; 52922) multiple types of recentchanges feeds (see Manual:$wgRCFeeds), including a machine readable JSON feed (JSONRCFeedFormatter). Right now the only feed exposed for Wikimedia sites is the "IRCColourfulRCFeed" via irc.wikimedia.org. There are multiple options on how to broadcast the new feed format, which are discussed below.

xmpp pub/sub
See http://xmpp.org/protocols/pubsub/
 * well known protocol, plenty of client libraries already available
 * w:ejabberd is scalable and well tested (was used by facebook, powers jabber.ru, etc) XMPP application server, plus already packaged in debian
 * leave it to third-parties to rebroadcast the data in whatever format they want (websockets)
 * XMPP packets can embed arbitrary XML subdocuments, which could carry structured data directly instead of embedding a JSON blob in XML or something --brion (105430)
 * See also: Recentchanges via XMPP, 17450 - Make Recent Changes available via XMPP

WebSockets

 * Useful for browser based tools.
 * node.js + nginx
 * Need to figure out how to make it scale and hardened
 * http://pusher.com/

IRC

 * Re-use irc.wikimedia.org, and create new channels like #en.wikipedia-json
 * Much easier for people who are already consuming the feed and just want to switch to machine readable data

Proposals for internal traffic
How MediaWiki should send the data to the proposed endpoint.

UDP
Implemented via the UDPRCFeedEngine class
 * Currently what is used via the udpmxircecho.py script (IRCD)
 * UDP may drop packets

ZeroMQ
Code is in 105117
 * "ZeroMQ is a high-performance asynchronous messaging library aimed at use in scalable distributed or concurrent applications." (w:ZeroMQ)
 * "Speaking as the person who introduced the current UDP solution: I don't know why you would want to continue using UDP. There's no reason to do that now that TCP queue daemons like zeromq exist. -- Tim Starling (talk) 06:17, 17 July 2013 (UTC)"

Redis
Pub/sub.

Implementation
RCStream was developed in response to this RFC. It uses WebSocket servers as backends behind an nginx endpoint. MediaWiki application servers are configured to publish a JSON-formatted RCFeed to Redis. The RCStream servers subscribe to Redis.