Apr 22 2008

NServiceBus Tutorial

Tag: Open Source,SOASymon Rottem @ 10:28 pm

Staying on the SOA theme, there was a post today on the NServiceBus mailing list from Mohamed Ahmed Meligy about the NServiceBus Tutorial he’s put together.

Mohammed is working for a company that’s been evaluating NServiceBus for an internal project and they’ve been kind enough to share the document with the rest of the community using a Creative Commons license.

The document will probably be evolving rapidly, but right now it’s an excellent starting point for anyone who’s trying to get their head around using NServiceBus as their messaging middleware, so go and take a look to get you off and running.


Apr 16 2008

The SOA Question

Tag: SOASymon Rottem @ 8:37 pm

For quite some time now I’ve been dabbling away at the edges of SOA trying to properly wrap my head around it so I can become a comfortable practitioner, but there’s a lot of guff out there from vendors which has been distracting.

I’ve been keeping up with Udi’s blog for a while now, where he often has good information about the SOA world which in turn led me to tinkering with NServiceBus.

More recently, however, I started reading Bill Pool’s Creative Abrasion blog.  He’s been talking about what SOA is, and what it isn’t and how to spot the difference, to cite a few recent examples.  These have proven an interesting read and I recommend Bill’s blog if you want to get your head around the concepts of SOA and how they work in your world.


Feb 23 2008

NServiceBus is Growing Up!

Tag: Open Source,SOASymon Rottem @ 4:52 am

NServiceBus is an Open Source Enterprise Service Bus framework released not so long ago by Udi Dahan and this week it got to it’s feet and wandered over to it’s new home at http://www.nservicebus.com. The site is still under construction, but it’s great to see a .NET OSS solution so recently released moving ahead so rapidly.

Over the last few months I’ve been evaluating it for use in an application and it’s certainly got a lot going for it. Configuration is not difficult and is planned to become even easier and using it is child’s play. There’s support for long running multi-message sagas, publish-subscribe semantics, pluggable transport layers, a vastly simplified and transport agnostic programming model and more – it’s definitely worth a look if you’re planning on building a scalable solution.

The only thing it’s been lacking so far has been documentation – a few months ago I submitted a patch with some code docs that might be used for generating API docs, but they’re a drop in the ocean and I really did them because I needed to read the code to really understand what was going on under the hood and marking up the methods with some code docs just seemed like a good idea to help me grok the whole thing.

What’s really needed is some guidance and tutorial style documentation and it looks like that’s beginning to get underway with the new site. Regardless, the source package comes with some great sample applications that demonstrate solutions to various common problems and since reading well written code is about the most basic method of revealing intentions the samples can work well to get you off the ground pending those additional docs.

I recently wrote a post called Do I Need Message Prioritisation? in which I discussed NServiceBus and some of the difficulties I was experiencing – I don’t think I gave it enough credit since it may not be the perfect fit for my specific problem, but I can certainly see it’s value and have plans to make heavy use of it in the future.

It’s really nice to have OSS alternatives available that don’t tie you to one specific vendor and I highly recommend NServiceBus as a software project to make friends with if you’re looking at writing scalable applications in an SOA context.


Feb 16 2008

Do I Need Message Prioritisation?

Tag: SOASymon Rottem @ 11:56 am

For a while now I’ve been working on modelling a service based application that accepts messages and sends them to a set of processing services that are spread across several hosts. One of the requirements is that the application should be able to provide different service level agreements for some message originators.

Since this looked like an Service Oriented Architecture (SOA) I started looking at an Enterprise Service Bus (ESB) to standardize the model for communicating between the applications, provide publish-subscribe semantics and allow me to abstract away the underlying message transport system.

At just the right moment Udi Dahan announced that he was releasing NServiceBus, his ESB implementation for .NET, so I started playing around with it. It’s OSS and written in C# but it was pretty new at the time I started looking at it so there wasn’t much documentation available. Regardless, it looked like a good fit so I rolled up my sleeves and started rummaging around in the source and playing with it…and it still looks like a good fit.

Everything seemed to be going well with the solution design until I looked at the SLA requirement and discovered that NServiceBus doesn’t have any notion of message priority. Since my initial approach had taken me toward using MSMQ as the underlying transport and MSMQ has some basic message priority support I thought I’d be able to use it from NServiceBus, but apparently not. A possible workaround was to implement separate queues for separate priorities but since MSMQ for the versions of Windows I’m targeting doesn’t provide remote transactional read it would be necessary to implement dispatchers and the proliferation of queues was starting to look pretty daunting.

So, next stop was to ask Udi so I dropped him an email. After a reasonably lengthy thread where he essentially suggested that trying to use priority in a queuing environment is probably not a great idea for several reasons he said he’d like to think further about the problem. Imagine my surprise and pleasure when he responded with a podcast entitled “Message Priority – You Aren’t Gonna Need It” in which he dedicated 20 minutes to provide further guidance.

His response was well worth listening to and answered a lot of the questions that had been banging around in my head but, as with most of Udi’s podcasts, it raised a whole new set of questions. The net result is that NServiceBus may still work for me but I think I need to start examining other message transports to find an easier path to my solution.

Now I find myself trying to wrap my head around space-based architectures and am looking for a .NET based implementation – if anyone knows of one please post me a comment.