Earlier this month at TechEd North America I gave a fairly new presentation that was only delivered once before (at the Connected Systems User Group in London) and I’m happy to say is now online for your viewing pleasure.

High Availability – A Contrarian View

Comments? Thoughts? Let me know.

After I had finished speaking at QCon London last March, I sat down for a short interview with the guys from InfoQ chatting about topics from CQRS, to DDD, to NServiceBus. I’m happy to say that the interview is now online with a full (and mostly accurate) transcript as well as with an MP3 download link.

Get it here: Udi Dahan on CQRS, DDD and NServiceBus

Update

The recording of the talk is now online and can be found here.

You can find the slides for my talk here.

Currently, the video is being graciously hosted by Jon Torresdal on his blog, so let’s hope that the bandwidth holds up.

Get it here.

The recording of the talk is online here.

There is one important thing that I didn’t have enough time to cover, but I want you to keep in mind as you’re watching this. It is that CQRS is applicable only *within* the context of a single service/BC – NOT across or between them.

Let me know what you think.

I’ll be discussing business service boundaries, publish/subscribe eventing, and business activity monitoring – with some time for questions at end.

Update: Recording is now online – here.

Hope to virtually see you there.

Here’s the details of the live meeting:

Start Time: Monday, June 01, 2009 07:00 PM GMT
End Time: Monday, June 01, 2009 08:30 PM GMT

Attendee URL: http://snipr.com/virtualaltnet (Live Meeting)

The quantity of deep, insightful questions was impressive and I hope that everybody got their most pressing issues addressed. I know that by the time you got home you probably had a whole bunch more – that happens all the time. This SOA/EDA style often gives a whole new perspective on system design.

You can find the slides online here.

Anyway, please feel free to send me your questions and I’ll do my best to answer them here.

When Ohad gets the recording online, I’ll make sure to link to it for those of you who couldn’t make it.

Feedback from attendees

From Ohad’s blog: “The talk was awesome … Udi really made our second usergroup meeting a huge success !”

Rotem Bloom: “היה פשוט הרצאה פצצה מי שלא מגיע מפסיד”, translated, “The presentation was ‘da bomb’, if you weren’t there, you missed out”

Adlai Maschiach: “הרצאה נ-ה-ד-ר-ת !”, translated, “A W-O-N-D-E-R-F-U-L presentation!”

Yitzhak Gootvilig: “הרצאה מעולה. מומלץ למצוא את הדרך להאזין להקלטה “, translated, “Excellent presentation. I strongly suggest finding a way to listen to the recording”

You can download the presentation as a PDF here.

You can find it here.
The slides can be found here.

I also gave this talk at TechEd Barcelona and wanted to thank the attendee who posted this comment:

“You’ve done it again. Everytime I attend a session of yours I leave the room with new insights and inspiration on how to improve my software…”

You made my day.

Here’s the link to the sample code I showed:

Download here.

Reliability, Availability, and Scalability
How to have your cake, and eat it too

Here’s the description:

Architects love the word “scalability”. We talk about transactions per second and page views per day and on and on. Of course, none of that scalability means anything if the system is down or if data gets lost or corrupted. Finding the right balance between reliability, availability, and scalability for the various parts of a system is critical to avoid unnecessarily costly solutions. This presentation will show a set of patterns that strikes this balance, their connection to supporting technologies, and their applicability across many enterprise domains. You can have it all.

SOA & DDD Early Bird

Jeffery already announced the early bird discount for the course I’m giving in October. You get 10% off for the next week or so. Sounds good.

Grid Presentation

I’m going to be giving my Avoid a Failed SOA talk to the Israeli Association of Grid Technologies on September 2nd. Full details here.

97 Nuggets

I’m really honoured to have taken part in the 97 Things Every Software Architect Should Know project. I don’t think there’s ever been such a concentration of world-class architects on any one project (I really don’t know how I got past the bouncer). Take a look.

IASA Webinar

I’ve mentioned before that I’m working on a course on Reliability, Availability, and Scalability for the International Association of Software Architects (IASA). That’s going to take a bit longer to get out, so in the mean time I’m going to be giving a webinar September 25th on the back of the IT Architect Regional Conference in Philadelphia. I’ll post the registration link when it comes online.

SD Best Practices

Finally, the guys from Dr. Dobb’s are going to be working me to the bone at the end of October for SD Best Practices in Boston . On top of the full-day nServiceBus tutorial, I’m going to be speaking every day. You can find my full list of sessions here. Apparently today’s the last day for the $700 early bird discount too.

Come up and say hi if you’re at one of these events. It’s always great meeting my readers.

Enjoy.

Here’s the powerpoint

And here’s the code

I’ll be giving my Avoid a Failed SOA talk (again). Apparently, I’m not the only one who’s been seeing one SOA project fail after another. Luckily, I’ve lived through enough of them to figure out what sort of things empirically have lead to failure, and now I’m telling the tale. One of the big reasons, by the way, is calling everything in the system a service (and no, adding a prefix doesn’t change anything – entity services, process services, etc).

I’m also going to be speaking about core design principles in my Intentions & Interfaces talk (which was quite a hit at QCon London). The interesting thing I’ve discovered over the years about design is that generics and dependency injection, when used together, can be used to create extensible systems with very little complexity. Not only that, but that this pattern is useful for all parts of a system, from communication, through data access, all the way to custom validation. As such, it can keep the complexity of the various technology stacks out of your core business logic, giving it a longer lease on life.

Finally, there’s also going to be a half-day tutorial on nServiceBus. I don’t want to go on-and-on about it here, but I can say that people who have attended this tutorial have come to me later telling me how they feel that they’ve had their eyes opened. I try to give just enough theory so that attendees can understand why nServiceBus exists, because after that using nServiceBus is pretty straight forward. This will be the first time I’m doing this in half-day format, so you’ll be getting the bottom-line, distilled version of this regularly full-day tutorial.

You can find the list of all my talks here, and for being the loyal reader you are, you get $100 bucks off the VIP price when you register using the code 8ASPK.

Hope to see you there.

You can find the slides here:

• Designing High Performance Persistent Domain Models
• Avoid a Failed SOA

It was a bit unfortunate that video wasn’t recorded for these talks, however since I previously gave the DomainModel talk at TechEd Barcelona you can watch the video (in English) but you have to log in to the TechEd site first, otherwise the DRM will block the video. I’m not sure if this is set up for TechEd Israel attendees, but I hope so.

Enjoy.

Watch in Media Player

NServiceBus Tutorial

I gave a full day tutorial on nServiceBus and we had a full house! The tutorial was about 90% how to think about distributed systems, and 10% mapping those concepts onto nServiceBus. I made an effort to cram about 3 days of a 5 day training course I give clients into one day, but I think I was only about 85% successful. People didn’t have the time needed to let things really sink in and ask questions, but the lively forums and skype conversations available will probably do the trick.

Jim Webber after looking at the unit testing features of nServiceBus had this to say:

“Oh my God – you’ve created testable middleware! It’ll never catch on. The vendors won’t have it.”

To which I replied that several vendors were already coming on board with their own implementations of transports and saga persistence. I have absolutely no intention, desire, or (quite frankly) the ability to write an enterprise-class middleware runtime. All I hope to do with nServiceBus is to make it so that developers use what’s out there in one, middleware-product-agnostic way that will make their code more robust and flexible.

MEST & Mark – REST & Stefan

It was also great finally meeting the head MESTian, Mark Little, who also happens to work for Redhat as SOA Technical Development Manager and Director of Standards in the JBoss division. It was interesting to see the difference between how I went about messaging in nServiceBus (full peer-to-peer including pub/sub) whereas most of the Java world has the messaging infrastructure handled by something database-like in a deployment/networking kind of perspective. If that’s the way things are done, then I can definitely appreciate the advantages of Space-Based Architectures.

And I even got to steal Stefan Tilkov’s RESTful ear for an hour or so before I had to jet back home. It looks like we MESTians and RESTians can be one big happy family. I’m guessing that our despise of WS connects us all at a deeper level

Core Design Principles

I also gave a talk about core design principles, “Intentions & Interfaces – making patterns concrete”, and it went over very well especially considering that that was the first time that I gave that talk. You can find the slides here. From the feedback I heard after the talk, I think many people were surprised how many different parts of a system can be designed this way, and how flexible it is without making the code any more complex. The message was this:

Make Roles Explicit

Despite its simplicity, that leads to IEntity, IValidator<T> where T : IEntity, (which I wrote about a year ago – generic validation) and with a bit of Service Locator capabilities, you can add a line of code to your infrastructure that will validate all entities before they’re sent from the client to the server.

It leads to IFetchingStrategy<T> for improved database loading performance (also a year old – better DDD implementation and the NHibernate implementation).

It’s also how nServiceBus does message handling – IMessage, IMessageHandler<T> where T: IMessage, ISaga<T> where T : IMessage.

San Francisco?

Just a quick shout to my readers in the San Francisco area, if you’d be interested in hearing these talks/tutorials, give the organizers of QCon a shout and they’ll bring me out. That’s actually what got me to London – one of the attendees of a talk I gave at Oredev in Sweden last November missed my tutorial there so he put in a request and that did it. (Thanks Jan, I appreciate it!)

If you’re in a different part of the world and you’d like to have me give one of these talks, or other ones (I have a fair amount of material on Domain Models/DDD and Occasionally Connected Smart Clients), I’d be happy to make the trip and see you there as well.

When I was at TechEd Barcelona last November (07), the morning after I flew in I experienced “the fish bowl” and Virtual TechEd for the first time. Anyway, after a short chat – and quite to my surprise, my interviewer, Paul Foster, decided that we should talk about nServiceBus.

So here it is. The Microsoft/Marketing friendly description of what nServiceBus is and how nicely it plays with things like WCF and WF. Always be a gracious guest. Don’t bite the hand that feeds you. But a nibble here and there – well, that you can get away with

Download:

Here’s the info:

Despite the recent flood of technologies and releases, distributed enterprise .net solution development remains as hard as ever. WCF and WF provide valuable runtime components, yet still leave open the risk of developers using the wrong combination of options and ending up with an unscalable solution.

In this session we’ll be looking at nServiceBus, an open-source communications framework, that guides developers into a style of development that is scalable by design. Including publish/subscribe facilities and long-running process state management, nServiceBus solves many of the challenges found in the enterprise. Finally, we’ll see the dynamic load-balancing features that enables endpoints to automatically adjust resource allocation in a grid-style deployment.

Date Jan 17, 2008 14:00 16:00

Location IGT Offices, Maskit 4, 5th Floor, Hertzelia

As usual, I’ll be putting up the slides and example code after the presentation.

The (pdf) presentation is here: Asynchronous Systems Architecture for the Web

The code sample is here: Asynchronous User Management Code Sample

In the sample, you can see the use of sagas to manage the user registration process; store user email and hashed password, send a confirmation “email”, when the user clicks the “link”, the web server will take the saga id found in the url, and send a message with that id. This will cause the saga to complete and the user to be written to the “database”.

Since I didn’t have an email component on my laptop, and I’m guessing you don’t either, the saga just writes the url to the console. Copy and paste it from there into the browser, and you’re good to go.

A Word on TimeoutExceptions

One other thing that I want to call to your attention. When stepping-through the code in the debugger, you’re liable to spend more time than the Transaction Coordinator likes, which will cause it to rollback and try the message again. This is supposed to happen and occurs by design.

When you’re actually working with a database in a high performance environment, there will be cases where one transaction locks a page of a table and may cause other transactions to either timeout or be chosen as victims and just tossed. The behavior that best handles this scenario is just to retry the transaction.

However, you don’t have to write ugly code that checks for the specific error codes of each specific database for your code to work properly. The infrastructure will automatically do that for you – just let the exception happen. No need to write any try-catch code.

The sample is built on the newly released version of nServiceBus (1.6.1) but already contains all the binaries so you don’t have to set anything up yourself.

What’s coming for nServiceBus

We’re working towards a 2.0 release in the June-July timeframe which, beyond having the necessary documentation, web site, samples and everything any self-respecting open-source project has, is going to have some amazing grid-style features that will make all the message-priority & dynamic-routing stuff look “so last year”. Stay tuned.

Looking forward to seeing you there.

Title:

Asynchronous Systems Architecture for the Web

Abstract:

The main lesson learned from the big sites – EBay, Amazon, etc over the past year has been to step away from the database and do more work in memory. The scalability benefits of asynchronous communication have become better known but many developers are still struggling with taking traditionally synchronous processes like user authentication and making them asynchronous. In this presentation, developers will be shown, step-by-step the patterns, frameworks, and code needed to implement all user management processes for a web site. We’ll be dealing with scalability, web farms, long-running workflows, as well as the security implications of our decisions.

If you’re interested in getting a kick-start with nServiceBus, I’ll be presenting a full day tutorial on it at QCon in London on March 11th. Here are the full details :

Title:

Build Scalable, Maintainable, Distributed Enterprise .NET Solutions with nServiceBus

Description:

Despite the recent flood of technologies and releases, distributed enterprise .net solution development remains as hard as ever.

WCF and WF provide valuable runtime components, yet still leave open the risk of developers using the wrong combination of options and ending up with an unscalable solution.

In this tutorial, developers will learn the specific patterns necessary to achieve scalability, as well as use supporting open-source frameworks to enable parallel development (and debugging!) of service interfaces, layers, and domain models.

After delving in to asynchronous message design, long-running workflow state management, and transaction-boundary placement developers will be able to design, debug, and deploy their specific distributed systems.

—

Hope to see you there.

Enjoy.

Watch in Media Player

I’ll be speaking about:

What to Test, and When

Now that unit testing and test-driven development have hit the mainstream, more and more companies are beginning to embrace these agile practices. What isn’t always clear is which practice is most useful in which scenario, and how alternatives like state-based testing and non-automated human-tester activities can be used most cost-effectively. Join Udi for a swoop through the development lifecycle and find out which questions you should be asking and when.

Adding Value to Message-Based SOAs with Workflow

In large-scale, loosely-coupled distributed systems, services communicate with each other using asynchronous messaging patterns. However, this event-based publish/subscribe communication is often incapable of expressing high-value, cross service, business processes. In this session, we will see exactly how a service is structured and examine the various layers that support the top-level SOA concepts as well as those needed for long-running workflows. Don’t write off SOA just yet; now that the hype’s dying down, we can finally get back to work.

And a full day seminar on NServiceBus

Using the open-source .NET ESB project “NServiceBus" we will do the design and implementation of long-running business processes and services according to the principles presented in the “Adding Value to Message-based SOAs with Workflow" session. We will go into the specifics of message design using publish/subscribe semantics, show how to set up message processing pipelines for separation of concerns between validation and business logic, as well as discuss the various failure scenarios that occur including poorly-formed messages, message loss, and business-level workflow timeouts. You will leave this tutorial with the tools, libraries, and example code to implement long-running, scalable, robust business processes between SOA style services in your company.

If you’re one of my regular readers, drop by and say hello, or, as I understand it in Swedish: hay