New Version of my Simple Kanban Board Application

Over the weekend I’ve worked on my Simple-Kanban application. Simple Kanban is a small Kanban board application in one Html file. New features are a data mode that displays the data in raw format for easier cut & paste and drag & drop support for moving stories around.

Simple Kanban Screenshot

There is a website now! I’ve added a small website at http://www.simple-kanban.com, where you can find new versions. I’ve also created a GitHub repository for Simple Kanban, where I’m planning to post the code (funny, the code is already open source as part of the Html file :-)

Much fun with using Simple-Kanban in your company, think lean!

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.


smokin
Creative Commons License photo credit: mudpig

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.

David Pollak (from Lift): “There’s no way to convert from XML to JSON because XML contains sequences not expressible in JSON”

Hmm[*]. Not sure if this is true (with CDATA, #Text and @attributes handled in some converters). For me the problem is more that there are too many ways to convert XML to JSON. For exampe the Badgerfish convention. Or the the Google and Yahoo versions. Or the XML.com way. And the Parker convention.

But the ways in Javascript to convert XML to JSON are either slow, very basic, use XSLT, use nasty Regex or cannot create simple JSON which feels JSON like.

* Note to self: Should start using Twitter for this [**].
** Did start Twitter

Update: Any ideas for a good XML to JSON conversion which feels JSON like (no need to be bidirectional)?

Update 2: I currently use XSLT with nice results, Safari doesn’t work yet and neither does Chrome. More to come.