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Archive for the ‘WCF’ Category



Bandwidth, Priority, and Service Contracts

Monday, August 20th, 2012

contractHere’s a small quick tip that can help you improve the performance of important use cases in your systems. It doesn’t require very many changes to your code and can improve matters when your system is under load but won’t make much of a difference when you have capacity to spare.

This is something I talk about in the first day of my course when going through the fallacies of distributed computing – specifically fallacy #3 which talks about bandwidth.

What about bandwidth?

When it comes to network bandwidth in your datacenter, there’s a pretty good chance you’re still on gigabit ethernet. When most developers hear that prefix, “giga”, there is an instantaneous translation in their brain to “so much I don’t need to worry about it”.

The thing is that it’s GigaBIT, not GigaByte, so we’re talking about 128 MBps.

Also, keep in mind that hardly anybody programs at the level of ethernet, we’re several layers up the stack. You can expect roughly 40% the bandwidth of ethernet up in TCP land due to its collision detection, exponential backoff, etc. So that’s roughly 50MBps, not counting overhead for serialization (which can be very significant if it’s text-based like XML or JSON).

In practice, you might be getting something like 25MBps – definitely not so much that you don’t even need to think about it.

Everybody’s talking scalability in terms of number of servers and memory, storage, CPU per server – but what about the network? More importantly, what happens when (not if) you run out? Well, the latency of your calls increase – and that can be quite substantial.

Business Priority

And now we get to the crux of the matter.

Consider a “Customer” web service with a bunch of methods on it, including these two: GenerateTopCustomersByRegionReport and MarkCustomerAsFraud.

Now, your system is under significant load and there’s just enough bandwidth left for one call to make it across the network without timing out. Two users invoke the functionality above – one doing the report, the other doing the fraud. Should the fact that one user clicked the button a millisecond before the other mean that the MarkCustomerAsFraud should be delayed to the point of failure?

I’m fairly sure that if we asked a business stakeholder the answer would be a clear no.

While we could try asking the network engineers to give higher priority to that webmethod, let’s face it, that’s never going to happen. Since both methods are on the same web service, clients are bound to the address where that web service is hosted, regardless of which methods they call.

The problem with “the” network

If there’s one word I loathe in the English language, it’s the word “the”.

Such a small word, tacked on in front of so many other words that, without you even noticing it, traps your mind into thinking you can have only one of that thing.

The network.
The database.

But you CAN have more than one – it’s YOUR system. Design it however you like.

Most servers (if not all) can have more than one network card these days. And even if yours couldn’t – you can ask your network engineers to set up multiple virtual networks on top of the physical network and divide up the bandwidth between them.

Putting it together

The next step is to simply put the MarkAsFraud method on a different web service. This way, you can decide at deployment time which web service should be hosted over which network.

When your system is under load, you will then be guaranteed that even if there are a large number of low priority calls being invoked, they will not use up the network bandwidth reserved for your higher priority calls. You will likely still need to take care of processing and other IO concerns on your servers, but if worst comes to worst, you can partition your server farm as well.

While this may sound a bit CQRS-ish but it would be more accurate to say that CQRS is a more specific case of this pattern – that of partitioning the API according to business priority.

One of the interesting things about messaging is that we tend to forgo the traditional “service contracts” where many methods are put together on a single “service”. Instead, each message definition stands on its own and can be routed to any destination.

In summary

If you are still using WCF and web services, be aware that these apparently little things can have an impact on how your system behaves under load. Even if you do use MSMQ under WCF, the traditional service contract made of multiple methods will still govern your routing.

If you do go all the way with this pattern, you’ll see that each of your service contracts ends up with only one method on it. This might make you wonder what’s the point of the whole service contract thing in WCF – that would be a very good issue to resolve.

Remember the first rule of remote communication – Don’t.



NServiceBus Videos Online

Sunday, June 26th, 2011

When I was at NDC a couple of weeks ago, I got together with Carl Franklin and we recorded a DNR-TV episode on NServiceBus. If you’re looking for a zero-to-sixty, code-centric explanation of NServiceBus – this is it.

NServiceBus on DNR-TV

For some more advanced stuff, I suggest looking at the Hidden NServiceBus Gems talk that I gave at Skills Matter the week after. Here we get into all sorts of things that you won’t tend to find by yourself through regular usage of NServiceBus.

Hidden NServiceBus Gems

Enjoy.



Polymorphism and Messaging

Thursday, January 13th, 2011

polymorphismOne of the questions that came up from my NServiceBus – .NET Service Bus Smackdown post was about the Polymorphic Message Dispatch and Polymorphic Message Routing features. People wanted to know what those are, why they’re important, and if other technologies (specifically WCF and BizTalk) support them.

Messaging Basics

First of all, when building a system using messaging, you don’t have methods that are invoked on some remote object (a.k.a “service”) to which you pass parameters. Instead, you use some generic piece of infrastructure (in the world of Java, this is most commonly a Message Broker) to send a message where a message can be thought of as a serializable class. Here’s an example of a message:

public class UserCreated : IMessage
{
    public Guid UserId { get; set; }
    public string Name { get; set; }
}

This message would be published using NServiceBus like this:

bus.Publish<UserCreated>( m =>
{
    m.UserId = Guid.NewGuid();
    m.Name = "John Smith";
});

This can be contrasted with RPC models like WCF where you need to define a “service” that has methods on it, where those methods accepts parameters. Sometimes developers try to make this more generic by having a single “service” with one method on it named something like “Process” where the parameter it accepts is of the type “object”, or they introduce generics like this: Process<T>(T message);

This is where Polymorphic Message Dispatch comes in:

Polymorphic Message Dispatch

While you can pull of the WCF generics thing, one thing that is more difficult (without writing your own dispatch model) is to have a pipeline of classes which can be invoked based on their relationship to the type passed in. Using NServiceBus, both of the following message handlers will be invoked when UserCreated arrives:

public class Persistence : IHandleMessages<UserCreated>
{
    public void Handle(UserCreated message) { }
}

public class Audit : IHandleMessages<IMessage>
{
    public void Handle(IMessage message) { }
}

Now some might say that WCF, BizTalk, and the .NET Service Bus allow you to do auditing in their own internal pipeline, and that’s true. The place where this becomes more powerful is when you need to build V2 of your system, and the publisher now publishes a slightly different event – that a user was created as a part of a campaign, requiring the subscriber to register statistics about the campaign. Of course, this event also means that a user was created. Here’s how you’d do that with NServiceBus:

public class UserCreatedFromCampaign : UserCreated
{
    public Guid CampaignId { get; set; }
}

//publisher code
bus.Publish<UserCreatedFromCampaign>( m =>
{
    m.UserId = Guid.NewGuid();
    m.Name = "John Smith";
    m.CampaignId = theCampaignId;
}

//subscriber code
public class Statistics : IHandleMessages<UserCreatedFromCampaign>
{
    public void Handle(UserCreatedFromCampaign message) { }
}

The important part is what you don’t see – since UserCreatedFromCampaign inherits from UserCrated, the Persistence handler we had from V1 will also be invoked, and so will the Audit handler of course. You don’t have to make your new code call the old code like you would in a method based dispatch model. This makes sure that the coupling in your service layer code remains constant over time as you grow the functionality of your system.

This was one of the main benefits mentioned by Rackspace in their use of NServiceBus (here):

“The main benefit NServiceBus has brought us so far is developer scalability due to lower coupling and higher consistency in our code.”

But, when looking at the above scenario, we can obviously expect that all sorts of things can happen in relation to campaigns – it is a separate concern, and thus should be handled by a separate subscriber. And this bring us to…

Polymorphic Message Routing

The challenge that we have here is that we no longer have a hierarchy where something clearly belongs on top of something else. We have users created and activities happening related to campaigns – that may happen in any combination. By having separate subscribers, we could then introduce new handlers/subscribers to our environment without touching or taking down any of the other subscribers. Here’s what the subscribers would look like:

public class Persistence : IHandleMessages<UserCreated>
{
    public void Handle(UserCreated message) { }
}

public class Statistics : IHandleMessages<CampaignActivityOccurred>
{
    public void Handle(CampaignActivityOccurred message) { }
}

But if each of the above messages were a class, how could we define a message which inherited from both?

Before answering that, we need to understand why the publisher wouldn’t just publish both of the above messages. You see, the publisher can’t make any assumptions about its subscribers – it could be that one of them has logic that correlates across both of these messages that could end up counting the occurrence as happening twice rather than once, possibly charging the account associated with the campaign twice. Publishing two messages results in two transactions when there really should have been one.

So, here’s how to define messages so that we can have multiple inheritance:

public interface UserCreated : IMessage
{
    Guid UserId { get; set; }
    string Name { get; set; }
}

public interface CampaignActivityOccurred : IMessage
{
    Guid CampaignId { get; set; }
    Guid ActivityId { get; set; }
}

public interface UserCreatedFromCampaign 
                 : UserCreated,
                   CampaignActivityOccurred 
{
}

And when the publisher publishes UserCreatedFromCampaign, the event would be routed to both the UserCreated subscriber and the CampaignActivityOccurred subscriber. The power of this approach is felt as we handle new requirements around purchases made related to a campaign. Now we can have another event which inherits from CampaignActivityOccurred and not have to worry since the existing subscriber will be routed those messages automatically.

Since WCF doesn’t have publish/subscribe capabilities, we might as well move along.

Not to throw a burning match on an ocean of oil, but REST doesn’t really support this either.

Not Content-Based Routing

This may sound like the content-based router pattern from EIP (CBR), but it’s not. The important difference is that there isn’t some part of the routing that depends on the structure of the messages. The major drawback of CBR is that it creates a central place in your system that needs to be changed any time *syntactic* changes happen to message structure *in addition to* to changes in the subscribers.

Now, this is where the BizTalk guys would say that “that’s why we can do message transformations”, and then the subscribers wouldn’t need to be changed. However, can we really know when getting a requirement that the change is syntactic and not semantic? I mean, it’s quite common that changes to message structures happen together with changes to processing logic.

You may be beginning to get the feeling that more and more logic is being sucked out of the subscribers into some monolithic black hole that is likely going to be unmaintainable and quite slow.

This is one of the main differences between using a bus and a broker – a bus supports the correct distribution of logic keeping the system loosely coupled; brokers are useful integration engines when you absolutely can’t change the applications being integrated. Enterprise Application Integration (EAI) brokers don’t usually make good Enterprise Service Bus (ESB) technology.

In Closing

NServiceBus has all sorts of features you didn’t know you needed until you saw what life could be like when you had them. Most of these features don’t have snazzy drag-and-drop demos that make people ooh-and-aah and TechEds and PDCs, but they’re really necessary to avoid finding yourself in yet another big-ball-of-mud code base telling your manager/customer (again) that it would be faster to rebuild the system from scratch than to implement that new requirement in the old one.

Take NServiceBus for a spin and see for yourself.



NServiceBus 2.5 Released

Friday, December 31st, 2010

Just before we usher in the new year, I’m happy to announce the release of NServiceBus version 2.5.

Go to the NServiceBus website

Yes, there’s a new logo, and the website’s been redesigned.
It’s been a long time coming – the previous version (2.0) was released in March.

I’m really quite excited about this version as it rolls up all the bug fixes and enhancements that customers have asked for as they ran version 2.0 under the most severe types of production environments. The next thing that is a big deal that many have been asking for is a licensed version of NServiceBus – that is, the ability to purchase a commercial license and receive support.

We all know how managers like having a throat to choke.

And now they’ll have one – NServiceBus Ltd is the company that will be providing licensing, services, and support for all customers’ NServiceBus needs. After more than 33,000 downloads and over 1000 developers in the community, the demand has really grown. Who would’ve thought all this would happen when I started NServiceBus 4 years ago (before it even had a name).

Why NServiceBus is better than WCF for your distributed systems

This question comes up repeatedly for people hearing about NServiceBus for the first time.

The answer is simple – reliability.

A system built with NServiceBus is so much more reliable to all kinds of production conditions than WCF that it’s hardly a fair comparison at all. While WCF can be configured to provide something kind of close to the same level of reliability, you need to do a fair amount of spelunking through the various options of netMsmqBinding to get it right.

The second reason to use NServiceBus instead of WCF is publish/subscribe.

The ability to make use of events and the observer pattern not just to achieve loose coupling within a single process, but across many processes, machines, and sites. Can you imagine going back to programming without events? Shudder. But that’s exactly what it’s like to use WCF in your distributed system. NServiceBus brings you the best of object-oriented programming but in a distributed and reliable infrastructure.

Don’t wait any longer

Take NServiceBus for a spin.

But things may look a bit different after you do…

RedPillBluePill

http://www.NServiceBus.com

And have a happy New Year.



Logical and Physical Architecture

Monday, November 8th, 2010

orthogonalOne architectural misunderstanding I see repeatedly in my work with clients is in the relationship between logical and physical architecture. The most common building-block of these misunderstandings is the web service (or it’s “upgraded” .net counterpart – the WCF service).

Don’t get me wrong, sometimes there is a place for a web service, just not everywhere.

So, what’s the problem?

Well, when developers and architects use web services as the building blocks of their designs, they are creating the same architecture for both the logical and physical elements of their system. Back in 1995, Philippe Kruchten documented his 4 + 1 Architectural View Model in which he outlined 4 + 1 different views that should be used to describe an architecture.

Even though since 1995 the number and types of recommended views of software architecture has evolved (with things like the Zachman Framework for enterprise architecture numbering some 30 views), there is broad agreement that (at the very least) the logical and physical artifacts should likely be designed differently.

Just because two distinct logical components have been identified in the architecture, that doesn’t necessarily mean they should be hosted separately (for example by making each one a web/wcf service). In fact, there are significant disadvantages to doing so (as described in the Fallacies of Distributed Computing).

In some cases, this mistake is exacerbated by a mistaking these components with SOA-type services, resulting in an attempt by developers to have each component have its own contract, which can then be independently versioned. This often results in the need for transformation between the structure of these so-called contracts, but not within the components themselves (oh-no, they’re “autonomous”), but rather in between them using some kind of “ESB” technology.

This architectural style is known as the Broker, Hub and Spoke, Mediator, and most importantly – not SOA. If you find a technology that fits this style perfectly (like BizTalk), that technology is not a Bus, not a Service Bus, and definitely not an Enterprise Service Bus.

One of the problems of this approach is that when any “service” contract changes, you have to change all the transformations in your broker that involve it. Unfortunately, most brokers have no unit-testing facility so it’s very much trial and error, and error, and error. The matter is even more serious since most brokers don’t enable you to have your transformations or orchestrations in source control, so you can’t diff to see what changed from the previous version.

It’s really amazing how much pain can be traced back to that one original misunderstanding.



NServiceBus – .NET Service Bus Smackdown

Wednesday, August 4th, 2010

I get this question quite often: “what is the difference between NServiceBus and the .NET Service Bus from Microsoft?” And I’m afraid the answer is that the two technologies were designed to handle a very different set of problems.

The .NET Service Bus was designed to bridge internet communications using the cloud to enable a variety of devices to communicate using a WCF-remote-procedure-call type of API. NServicebus was designed to simplify the design of on-premise distributed systems using reliable messaging.

Still, people seem to want a kind of comparison, so here’s a quick one off-the-top-of-my-head:

Feature .NET Service Bus NServiceBus
Cloud-based messaging Yes No
Internet-spanning communication Yes Yes – via additional gateway process
Lightweight client support Yes Yes – via exposed WCF endpoint
Full duplex communication Yes Yes – not including lightweight clients
Publish / Subscribe support Yes Yes
Interop with non-.Net platforms Yes Yes
Maximum message size 64 KB 4012 KB
Long-running stateful processes Using WF on top Yes
On-premise messaging No Yes
Client can send messages if server is offline No Yes
Poison message detection and dispatching No Yes
Poison messages re-processing No Yes
Subscriptions persist after restart No Yes
Polymorphic message dispatch No Yes
Polymorphic message routing No Yes
Message-driven unit testing No Yes

This is not meant to be an exhaustive list, or even an accurate representation of the relative strengths and weaknesses of the technologies because, as I said, they’re designed for different purposes.

One could even plug the .NET Service Bus into NServiceBus instead of its MSMQ transport to get broad reach where required, and then switching back to the on-premise strengths of MSMQ. The pluggability of NServiceBus makes it easy to swap out almost all implementation components like the subscription storage, transport, authorization mechanisms, containers, etc.

For more information on the .NET Service Bus see the Azure AppFabric page. Juval Lowey also has a nice article on it up on MSDN magazine here.

For more information on NServiceBus see the new Particular.net site. Also take a look at the pages giving you comparisons to WCF and BizTalk.



Hanselminutes on NServiceBus

Friday, August 21st, 2009


Yesterday me and Scott virtually sat down to have a chat about NServiceBus and service buses in general. While we didn’t get in to many of the more advanced parts, you may find it an interesting introduction to the topic as well as saving yourself the costly mistake of implementing a broker instead of a bus (yes – they’re actually two different things).

Take a listen.



A Queue Isn’t An Implementation Detail

Monday, May 25th, 2009

It’s hard to believe that this continues to pop up even as WCF is reaching its fourth version (emphasis mine):

“A common complaint is that the first call on a client object takes some disproportionately large amount of time, usually ten seconds or more, while successive calls are instantaneous. There are many reasons why this might happen so there’s no generic resolution for this problem.” — Nicholas Allen

The thing is that there IS a generic solution to this problem.

It’s queued messaging.

The only thing is that you have to give up talking to your services as if they were regular objects – calling methods on them and expecting a response. In other words, designing a distributed systems isn’t like designing a regular OO system just with some WCF sprinkled on top.

Even when trying to do fire and forget messaging on top of WCF (void method calls with the OneWay attribute), the underlying channel can still block your thread, as Nick mentioned.

A queue isn’t an implementation detail.
It’s the primary architectural abstraction of a distributed system.



MSDN Magazine Smart Client Article

Saturday, March 28th, 2009

image

My article on “optimizing a large-scale Software+Services application” has been published in the April edition of MSDN Magazine.

Here’s a short excerpt:

“We had to juggle occasional connectivity, data synchronization, and publish/subscribe all at the same time. We learned that we couldn’t solve all problems either client-side or server-side, but rather that an integrated approach was needed since any changes on one side needed corresponding changes on the other side.”

Continue reading…



Make WCF and WF as Scalable and Robust as NServiceBus

Monday, June 30th, 2008

This topic is getting more play as more people are using WCF and WF in real-world scenarios, so I thought I’d pull the things that I’ve been watching in this space together:

Reliabilitydoctor

Locking in SqlWorkflowPersistenceService (via Ron Jacobs) where, if you want predictable persistence (MS: ‘none of our customers asked for this to be easy’), you need to use a custom activity (which Ron was kind enough to supply).

“Given what I learned today I’d have to say that I’d be very careful about using workflows with an optimistic locking.  Detecting these types of situations is not that simple.”

Let’s think about that. If we’re doing pessimistic locking, we get into the problem of, if a host restarts (as the result of a critical windows patch or some other unexpected occurrence), that the workflow won’t be able to be handled by any other host in the meantime (you didn’t care so much about your SLA, did you?).

Luckily, someone’s come up with a hack that works around this robustness problem in Scalable Workflow Persistence and Ownership.

“So this code will attempt to load workflow instances with expired locks every second. Is it a hack? Yes. But without one of two things in the SqlWorkflowPersistenceService its the sort of code you have to write to pick up unlocked workflow instances robustly.”

This will seriously churn the table used to store your workflows, decreasing performance of workflows that haven’t timed out. Oh well.

Testability

Implementing WCF Services without Referencing WCF (via Mark Seemann):

“More than a year ago, I wrote my first post on unit testing WCF services. One of my points back then was that you have to be careful that the service implementation doesn’t use any of the services provided by the WCF runtime environment (if you want to keep the service testable). As soon as you invoke something like OperationContext.Current, your code is not going to work in a unit testing scenario, but only when hosted by WCF.”

After pointing out some of the more basic difficulties in testability a straightforward WCF implementation brings, Mark turns the heat up in his follow-up post, Modifying Behavior of WCF-Free Service Implementations:

“Perhaps you need to control the service’s ConcurrencyMode, or perhaps you need to set UseSynchronizationContext. These options are typically controlled by the ServiceBehaviorAttribute. You may also want to provide an IInstanceProvider via a custom attribute that implements IContractBehavior. However, you can’t set these attributes on the service implementation itself, since it mustn’t have a reference to System.ServiceModel.”

Wow – all the things required to make a WCF service scalable and thread-safe make it difficult to test. In the end, we’re beginning to see how many hoops we have to go through in order to get separation of concerns, but until we can take all this and get it out of our application code, it’s an untenable solution. I hope Mark will continue with this series, if only so I can take the framework that might grow out of it and use it as a generic WCF transport for NServiceBus.

Comparisonapples and oranges

After the Neuron-NServiceBus comparison that Sam and I had, we talked some more. After going through some of the rational and thinking, Sam even put nServiceBus into his WCF-Neuron comparison talk. Sam had this to say about nServiceBus:

“The bottom line is: I like what I see. Although it’s a framework, not an ESB product like Neuron, it’s a powerful framework that takes the right approach on SOA and enforces a paradigm of reliable one-way, *non-blocking* calls. That is the point of the talk tonight overall; we need to get away from the stack world of synchronous RPC calls to true asynchronous non-blocking message based SOA systems.”

The main concern I have with a WCF+WF based solution is that developers need to know a lot in order to make it testable, scalable, and robust. In nServiceBus, that’s baked into the design. It would be extremely difficult for a developer writing application logic to interfere with when persistence needs to happen, or the concurrency strategy of long-running workflows. The fact that message handlers in the service layer don’t need concurrency modes, instance providers, or any of that junk make them testable by default.



   


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Vadim Mesonzhnik, Development Project Lead at Polycom
“When we were faced with a task of creating a high performance server for a video-tele conferencing domain we decided to opt for a stateless cluster with SQL server approach. In order to confirm our decision we invited Udi.

After carefully listening for 2 hours he said: "With your kind of high availability and performance requirements you don’t want to go with stateless architecture."

One simple sentence saved us from implementing a wrong product and finding that out after years of development. No matter whether our former decisions were confirmed or altered, it gave us great confidence to move forward relying on the experience, industry best-practices and time-proven techniques that Udi shared with us.
It was a distinct pleasure and a unique opportunity to learn from someone who is among the best at what he does.”

Jack Van Hoof Jack Van Hoof, Enterprise Integration Architect at Dutch Railways
“Udi is a respected visionary on SOA and EDA, whose opinion I most of the time (if not always) highly agree with. The nice thing about Udi is that he is able to explain architectural concepts in terms of practical code-level examples.”

Neil Robbins Neil Robbins, Applications Architect at Brit Insurance
“Having followed Udi's blog and other writings for a number of years I attended Udi's two day course on 'Loosely Coupled Messaging with NServiceBus' at SkillsMatter, London.

I would strongly recommend this course to anyone with an interest in how to develop IT systems which provide immediate and future fitness for purpose. An influential and innovative thought leader and practitioner in his field, Udi demonstrates and shares a phenomenally in depth knowledge that proves his position as one of the premier experts in his field globally.

The course has enhanced my knowledge and skills in ways that I am able to immediately apply to provide benefits to my employer. Additionally though I will be able to build upon what I learned in my 2 days with Udi and have no doubt that it will only enhance my future career.

I cannot recommend Udi, and his courses, highly enough.”

Nick Malik Nick Malik, Enterprise Architect at Microsoft Corporation
You are an excellent speaker and trainer, Udi, and I've had the fortunate experience of having attended one of your presentations. I believe that you are a knowledgable and intelligent man.”

Sean Farmar Sean Farmar, Chief Technical Architect at Candidate Manager Ltd
“Udi has provided us with guidance in system architecture and supports our implementation of NServiceBus in our core business application.

He accompanied us in all stages of our development cycle and helped us put vision into real life distributed scalable software. He brought fresh thinking, great in depth of understanding software, and ongoing support that proved as valuable and cost effective.

Udi has the unique ability to analyze the business problem and come up with a simple and elegant solution for the code and the business alike.
With Udi's attention to details, and knowledge we avoided pit falls that would cost us dearly.”

Børge Hansen Børge Hansen, Architect Advisor at Microsoft
“Udi delivered a 5 hour long workshop on SOA for aspiring architects in Norway. While keeping everyone awake and excited Udi gave us some great insights and really delivered on making complex software challenges simple. Truly the software simplist.”

Motty Cohen, SW Manager at KorenTec Technologies
“I know Udi very well from our mutual work at KorenTec. During the analysis and design of a complex, distributed C4I system - where the basic concepts of NServiceBus start to emerge - I gained a lot of "Udi's hours" so I can surely say that he is a professional, skilled architect with fresh ideas and unique perspective for solving complex architecture challenges. His ideas, concepts and parts of the artifacts are the basis of several state-of-the-art C4I systems that I was involved in their architecture design.”

Aaron Jensen Aaron Jensen, VP of Engineering at Eleutian Technology
Awesome. Just awesome.

We’d been meaning to delve into messaging at Eleutian after multiple discussions with and blog posts from Greg Young and Udi Dahan in the past. We weren’t entirely sure where to start, how to start, what tools to use, how to use them, etc. Being able to sit in a room with Udi for an entire week while he described exactly how, why and what he does to tackle a massive enterprise system was invaluable to say the least.

We now have a much better direction and, more importantly, have the confidence we need to start introducing these powerful concepts into production at Eleutian.”

Gad Rosenthal Gad Rosenthal, Department Manager at Retalix
“A thinking person. Brought fresh and valuable ideas that helped us in architecting our product. When recommending a solution he supports it with evidence and detail so you can successfully act based on it. Udi's support "comes on all levels" - As the solution architect through to the detailed class design. Trustworthy!”

Chris Bilson Chris Bilson, Developer at Russell Investment Group
“I had the pleasure of attending a workshop Udi led at the Seattle ALT.NET conference in February 2009. I have been reading Udi's articles and listening to his podcasts for a long time and have always looked to him as a source of advice on software architecture.
When I actually met him and talked to him I was even more impressed. Not only is Udi an extremely likable person, he's got that rare gift of being able to explain complex concepts and ideas in a way that is easy to understand.
All the attendees of the workshop greatly appreciate the time he spent with us and the amazing insights into service oriented architecture he shared with us.”

Alexey Shestialtynov Alexey Shestialtynov, Senior .Net Developer at Candidate Manager
“I met Udi at Candidate Manager where he was brought in part-time as a consultant to help the company make its flagship product more scalable. For me, even after 30 years in software development, working with Udi was a great learning experience. I simply love his fresh ideas and architecture insights.
As we all know it is not enough to be armed with best tools and technologies to be successful in software - there is still human factor involved. When, as it happens, the project got in trouble, management asked Udi to step into a leadership role and bring it back on track. This he did in the span of a month. I can only wish that things had been done this way from the very beginning.
I look forward to working with Udi again in the future.”

Christopher Bennage Christopher Bennage, President at Blue Spire Consulting, Inc.
“My company was hired to be the primary development team for a large scale and highly distributed application. Since these are not necessarily everyday requirements, we wanted to bring in some additional expertise. We chose Udi because of his blogging, podcasting, and speaking. We asked him to to review our architectural strategy as well as the overall viability of project.
I was very impressed, as Udi demonstrated a broad understanding of the sorts of problems we would face. His advice was honest and unbiased and very pragmatic. Whenever I questioned him on particular points, he was able to backup his opinion with real life examples. I was also impressed with his clarity and precision. He was very careful to untangle the meaning of words that might be overloaded or otherwise confusing. While Udi's hourly rate may not be the cheapest, the ROI is undoubtedly a deal. I would highly recommend consulting with Udi.”

Robert Lewkovich, Product / Development Manager at Eggs Overnight
“Udi's advice and consulting were a huge time saver for the project I'm responsible for. The $ spent were well worth it and provided me with a more complete understanding of nServiceBus and most importantly in helping make the correct architectural decisions earlier thereby reducing later, and more expensive, rework.”

Ray Houston Ray Houston, Director of Development at TOPAZ Technologies
“Udi's SOA class made me smart - it was awesome.

The class was very well put together. The materials were clear and concise and Udi did a fantastic job presenting it. It was a good mixture of lecture, coding, and question and answer. I fully expected that I would be taking notes like crazy, but it was so well laid out that the only thing I wrote down the entire course was what I wanted for lunch. Udi provided us with all the lecture materials and everyone has access to all of the samples which are in the nServiceBus trunk.

Now I know why Udi is the "Software Simplist." I was amazed to find that all the code and solutions were indeed very simple. The patterns that Udi presented keep things simple by isolating complexity so that it doesn't creep into your day to day code. The domain code looks the same if it's running in a single process or if it's running in 100 processes.”

Ian Cooper Ian Cooper, Team Lead at Beazley
“Udi is one of the leaders in the .Net development community, one of the truly smart guys who do not just get best architectural practice well enough to educate others but drives innovation. Udi consistently challenges my thinking in ways that make me better at what I do.”

Liron Levy, Team Leader at Rafael
“I've met Udi when I worked as a team leader in Rafael. One of the most senior managers there knew Udi because he was doing superb architecture job in another Rafael project and he recommended bringing him on board to help the project I was leading.
Udi brought with him fresh solutions and invaluable deep architecture insights. He is an authority on SOA (service oriented architecture) and this was a tremendous help in our project.
On the personal level - Udi is a great communicator and can persuade even the most difficult audiences (I was part of such an audience myself..) by bringing sound explanations that draw on his extensive knowledge in the software business. Working with Udi was a great learning experience for me, and I'll be happy to work with him again in the future.”

Adam Dymitruk Adam Dymitruk, Director of IT at Apara Systems
“I met Udi for the first time at DevTeach in Montreal back in early 2007. While Udi is usually involved in SOA subjects, his knowledge spans all of a software development company's concerns. I would not hesitate to recommend Udi for any company that needs excellent leadership, mentoring, problem solving, application of patterns, implementation of methodologies and straight out solution development.
There are very few people in the world that are as dedicated to their craft as Udi is to his. At ALT.NET Seattle, Udi explained many core ideas about SOA. The team that I brought with me found his workshop and other talks the highlight of the event and provided the most value to us and our organization. I am thrilled to have the opportunity to recommend him.”

Eytan Michaeli Eytan Michaeli, CTO Korentec
“Udi was responsible for a major project in the company, and as a chief architect designed a complex multi server C4I system with many innovations and excellent performance.”


Carl Kenne Carl Kenne, .Net Consultant at Dotway AB
“Udi's session "DDD in Enterprise apps" was truly an eye opener. Udi has a great ability to explain complex enterprise designs in a very comprehensive and inspiring way. I've seen several sessions on both DDD and SOA in the past, but Udi puts it in a completly new perspective and makes us understand what it's all really about. If you ever have a chance to see any of Udi's sessions in the future, take it!”

Avi Nehama, R&D Project Manager at Retalix
“Not only that Udi is a briliant software architecture consultant, he also has remarkable abilities to present complex ideas in a simple and concise manner, and...
always with a smile. Udi is indeed a top-league professional!”

Ben Scheirman Ben Scheirman, Lead Developer at CenterPoint Energy
“Udi is one of those rare people who not only deeply understands SOA and domain driven design, but also eloquently conveys that in an easy to grasp way. He is patient, polite, and easy to talk to. I'm extremely glad I came to his workshop on SOA.”

Scott C. Reynolds Scott C. Reynolds, Director of Software Engineering at CBLPath
“Udi is consistently advancing the state of thought in software architecture, service orientation, and domain modeling.
His mastery of the technologies and techniques is second to none, but he pairs that with a singular ability to listen and communicate effectively with all parties, technical and non, to help people arrive at context-appropriate solutions. Every time I have worked with Udi, or attended a talk of his, or just had a conversation with him I have come away from it enriched with new understanding about the ideas discussed.”

Evgeny-Hen Osipow, Head of R&D at PCLine
“Udi has helped PCLine on projects by implementing architectural blueprints demonstrating the value of simple design and code.”

Rhys Campbell Rhys Campbell, Owner at Artemis West
“For many years I have been following the works of Udi. His explanation of often complex design and architectural concepts are so cleanly broken down that even the most junior of architects can begin to understand these concepts. These concepts however tend to typify the "real world" problems we face daily so even the most experienced software expert will find himself in an "Aha!" moment when following Udi teachings.
It was a pleasure to finally meet Udi in Seattle Alt.Net OpenSpaces 2008, where I was pleasantly surprised at how down-to-earth and approachable he was. His depth and breadth of software knowledge also became apparent when discussion with his peers quickly dove deep in to the problems we current face. If given the opportunity to work with or recommend Udi I would quickly take that chance. When I think .Net Architecture, I think Udi.”

Sverre Hundeide Sverre Hundeide, Senior Consultant at Objectware
“Udi had been hired to present the third LEAP master class in Oslo. He is an well known international expert on enterprise software architecture and design, and is the author of the open source messaging framework nServiceBus. The entire class was based on discussion and interaction with the audience, and the only Power Point slide used was the one showing the agenda.
He started out with sketching a naive traditional n-tier application (big ball of mud), and based on suggestions from the audience we explored different solutions which might improve the solution. Whatever suggestions we threw at him, he always had a thoroughly considered answer describing pros and cons with the suggested solution. He obviously has a lot of experience with real world enterprise SOA applications.”

Raphaël Wouters Raphaël Wouters, Owner/Managing Partner at Medinternals
“I attended Udi's excellent course 'Advanced Distributed System Design with SOA and DDD' at Skillsmatter. Few people can truly claim such a high skill and expertise level, present it using a pragmatic, concrete no-nonsense approach and still stay reachable.”

Nimrod Peleg Nimrod Peleg, Lab Engineer at Technion IIT
“One of the best programmers and software engineer I've ever met, creative, knows how to design and implemet, very collaborative and finally - the applications he designed implemeted work for many years without any problems!

Jose Manuel Beas
“When I attended Udi's SOA Workshop, then it suddenly changed my view of what Service Oriented Architectures were all about. Udi explained complex concepts very clearly and created a very productive discussion environment where all the attendees could learn a lot. I strongly recommend hiring Udi.”

Daniel Jin Daniel Jin, Senior Lead Developer at PJM Interconnection
“Udi is one of the top SOA guru in the .NET space. He is always eager to help others by sharing his knowledge and experiences. His blog articles often offer deep insights and is a invaluable resource. I highly recommend him.”

Pasi Taive Pasi Taive, Chief Architect at Tieto
“I attended both of Udi's "UI Composition Key to SOA Success" and "DDD in Enterprise Apps" sessions and they were exceptionally good. I will definitely participate in his sessions again. Udi is a great presenter and has the ability to explain complex issues in a manner that everyone understands.”

Eran Sagi, Software Architect at HP
“So far, I heard about Service Oriented architecture all over. Everyone mentions it – the big buzz word. But, when I actually asked someone for what does it really mean, no one managed to give me a complete satisfied answer. Finally in his excellent course “Advanced Distributed Systems”, I got the answers I was looking for. Udi went over the different motivations (principles) of Services Oriented, explained them well one by one, and showed how each one could be technically addressed using NService bus. In his course, Udi also explain the way of thinking when coming to design a Service Oriented system. What are the questions you need to ask yourself in order to shape your system, place the logic in the right places for best Service Oriented system.

I would recommend this course for any architect or developer who deals with distributed system, but not only. In my work we do not have a real distributed system, but one PC which host both the UI application and the different services inside, all communicating via WCF. I found that many of the architecture principles and motivations of SOA apply for our system as well. Enough that you have SW partitioned into components and most of the principles becomes relevant to you as well. Bottom line – an excellent course recommended to any SW Architect, or any developer dealing with distributed system.”

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