ActiveMQ vs. Jabber
If you have or plan an application with synchronous communications over an external API, it will sooner or later break. Why do we need asynchronous communications? Matt Tucker is clear about that:
Take, for example, Twitter. High Scalability recently covered the load stats on Twitter reporting that they average 200-300 connections per second with spikes that climb to 800 connections per second. Their MySQL server handles 2,400 requests per second! Recently, the [2008] Macworld keynote became the most recent culprit for causing Twitter to cut off its API, which has 10x the load of their website.
When one of my web pet projects needed a messaging backbone which extends to the browser. Whenever a resource did change on the server, all users watching the resource should get a notification without need to reload their browser. Two candidates are Javascript for ActiveMQ, which uses Comet
ActiveMQ supports Ajax which is an Asychronous Javascript And Xml mechanism for real time web applications. This means you can create highly real time web applications taking full advantage of the publish/subscribe nature of ActiveMQ.
ActiveMQ is a messaging bus, often used as an Enterprise Service bus as mentioned in my recent concurrency rant. Components can send messages to the bus and subscribe to topics.
The other unsuspected contender is Javascript for Jabber. Jabber with the XMPP protocol is usally used for sending chat messages. Comparing these two and my thoughts:
ActiveMQ
- Standard solution, JMS based
- Routing solutions like Camel available
- Easy access for different languages via Stomp
- Attach Jabber as a service
- Notification easily over topics
Jabber
- Free OpenFire server
- Messaging with only one user with UUID for resource which did change
- Messaging with many users, who join one chat room
- Chat rooms as topics
- Server side filtering? How to make it secure, that people only get their own messages?
In the end I decided to go with Jabber/XMPP. The main points for me have been:
- Server does scale to connections
- Chat client can be used for debugging
- Very easy to use with different programming languages
- Presence protocol to detect services
- Easy to implement additional chat solution
This worked quite well as a spike. I followed a similar mode as Adrian Sutton, who had good experiences with Jabber/XMPP too when spiking a cache solution:
We grabbed the Smack API and started playing with it and quickly discovered that sending and receiving messages was ridiculously easy. It turns out that the absolute simplest way you can minimize stale data in your caches is to simply have all the servers join a preconfigured chat room. Whenever they save a change to a resource they send a message to the room with the unique ID of that resource and whenever they receive a message from the room they assume it’s a unique ID and remove any cached versions of that resource.
Though I had some major problems accessing Jabber consistently from Javascript. With more on messaging in the backend, I would have went with ActiveMQ as a message bus. And perhaps I might move to ActiveMQ in the backend and then I’m still free to attach Jabber on top of that and keep the frontend code. Best from two worlds.
Think innovative, use technologies in a way to help you. Jabber/XMPP is more than a chat protocol.
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I played around with the Smack API a few months ago and was very surprised about the ease of use. Not that I have an actual use case for it, but it’s a nice thought to use this protocols for real code that is *not* a messenger.