Udi Dahan   Udi Dahan – The Software Simplist
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Visual Cobol, Enterprise Processes, and SOA

Wednesday, April 23rd, 2008

There’s a fairly intense discussion going on these days amongst the SOA illuminati. In the hopes that people will see me standing beside them and conclude that I too know something, I’ve decided to chip in.

Jim brought the concept of cohesion to the regular SOA discussions around loose coupling in his post Anemic Service Model, which I think, all in all, is a very good idea.

Naïve Service Composition

image Jim first calls out a common anti-pattern that seems to have become quite rampant – I’d call it naïve service composition if only the things being composed could even be called services. And I think the tone being set is correct – a service needs to meet a stronger set of criteria than just being able to be composed. Multiple services sharing the same logical data store (in that the same actual rows/data elements are managed by multiple services) probably means there’s an encapsulation problem here. I agree with Jim sentiment here:

“On the one hand we’re inclined, and indeed encouraged by the SOA brigade, to think of this architecture as a good fit for purpose because it is very loosely coupled. Since every component or service is decoupled from every other component or service it should be possible to arrange and re-arrange them in a Lego-style in a myriad of useful ways. Building out “business services” from some more fundamental set of services is how the books tell us to do it. In fact we could even do that quite easily with point-and-[click] BPM tools, ruling out such overheads as developers and change management along the way. Right?”

MVC? There are, like, 6 of them!image

However, I disagree with some of the conclusions that Jim draws from that point. Jim states “build your services to implement business processes”, and that services are “just an instance of MVC”. I’m going to leave alone the MVC statement since there are like 6 documented kinds of MVC not including the Front Controller stuff that the web guys are now calling MVC. I’m going to focus on the business process advice. JJ also doesn’t seem to agree with this advice. As Savas has already taken issue with the tone of JJ’s response, I’ll keep my focus on the content.

Visual Cobol

First of all, in my previous conversations with Jim he had already denounced the procedural nature of composing higher-level business processes out of smaller services which implement small bits of common activities. Visual Cobol was how he described it. In JJ’s follow-up post, he called out the necessary aspect of autonomy that jives with Jim’s cohesion principle.

I’m a bit concerned about the way JJ tends to version what SOA means over time. It might make it impossible to have intelligent design discussions without tagging each sentence with “as SOA meant in 2006”. I acknowledge that the accepted meaning of SOA by various vendors has changed over the years. However, I’ve found that meanings rooted in decades of computer science tend to last and provide value that outlasts much of the industry-buzzword-bingo (SOA 2.0 anyone?).

Cohesion, Business Domains, and Business Processes

image My view of the original cohesion principles Steve discusses in his 2005 article Old Measures for New Services takes a business spin to Functional Cohesion:

A service should be responsible for one business domain.

If we jump off from this point, we’ll see that certain business processes which occur entirely in one business domain are fully encapsulated, whereas those macro-processes which cross many domains (like Order to Cash) cross multiple services – they do not become a service since that would break the “one business domain” rule. Given that services are loosely coupled, avoiding temporal coupling leads to services raising events. Thus, macro-processes are really just a series of events of various services where each service does its own internal business processes.

Enterprise Processes >> Business Processes

I think that maybe some of the difficulty in discussing concrete SOA guidance has to do with granularity. I’ve started calling those macro-processes something different from business processes, and that may just bring me full circle to Jim’s guidance.

An Enterprise Process is any process which involves multiple business domains.

Under that definition, a service may be responsible for multiple business processes in the same business domain. But still, one business process is usually not a service by itself.

Business Components & Autonomous Components to the Rescue

image Finally, by introducing the additional levels of decomposition of business components and autonomous components I’ve found that we can focus the discourse on one concern at a time. My presentation on the topic can be found here. The 30 second pitch is this:

Business domains are inherently partitionable – data and rules. A business component represents one partition. An example of this is the domain of Sales being partitioned by strategic and non-strategic customers. Although the data structure might be similar or the same, the actual rows/data elements are not shared. Rules around discounts are different.

Within a business component, different activities should not interfere with each other. An autonomous component represents one activity. In our example, reporting on orders from strategic customers should not interfere with accepting their orders. As such, those activities should have different messages coming in on different endpoints. Each endpoint could have different characteristics, like durability. Losing a request for a report when a server restarts isn’t a big deal, however not a good idea for orders.

For more information you could check out these episodes from my podcast:

Business and Autonomous Components in SOA

Using Autonomous Components for SLAs in SOA

Questions and comments are always welcome.

Scalability Article up on InfoQ

Thursday, April 10th, 2008

I’ve published a new article on performance and scalability on InfoQ:

Spectacular Scalability with Smart Service Contracts

In this article, I attempt to debunk some of the myths around stateless-ness as the key to scalability.

Here’s how it starts:

It was a sunny day in June 2005 and our spirits were high as we watched the new ordering system we’d worked on for the past 2 years go live in our production environment. Our partners began sending us orders and our monitoring system showed us that everything looked good. After an hour or so, our COO sent out an email to our strategic partners letting them know that they should send their orders to the new system. 5 minutes later, one server went down. A minute after that, 2 more went down. Partners started calling in. We knew that we wouldn’t be seeing any of that sun for a while.

The system that was supposed to increase the profitability of orders from strategic partners crumbled. The then seething COO emailed the strategic partners again, this time to ask them to return to the old system. The weird thing was that although we had servers to spare, just a few orders from a strategic customer could bring a server to its knees. The system could scale to large numbers of regular partners, but couldn’t handle even a few strategic partners.

This is the story of what we did wrong, what we did to fix it, and how it all worked out.

Continue reading…


Friday, March 28th, 2008

Ted says it really well, and let me add a big +1.

Note to those who didn’t attend the session: you didn’t hear me say it, so I’ll repeat it: I hate WSDL almost as much as I hate Las Vegas. Ask me why sometime, or if I get enough of a critical mass of questions, I’ll blog it. If you’ve seen me do talks on Web Services, though, you’ve probably heard the rant: WSDL creates tightly-coupled endpoints precisely where loose coupling is necessary, WSDL encourages schema definitions that are inflexible and unevolvable, and WSDL intrinsically assumes a synchronous client-server invocation model that doesn’t really meet the scalability or feature needs of the modern enterprise. And that’s just for starters.

I hate WSDL.

I still hate Vegas more, though.

image Web Services, and WSDL by connection have taken hold of the industry like cancer – inhibiting the minds of otherwise intelligent developers and architects. Whenever I get the “Web Services Question” (Does X support Web Services – where X is some design pattern, tool, and sometimes nServiceBus), I have to suppress an urge to groan – I’ve got the question that many times. The other day I was at a client and Sam, their head architect asked me that question. I gave my stock response:

“When you say ‘Web Services’, are you referring to SOAP or WSDL, and is HTTP a necessary component too?”

See how good I got at the suppressing thing?

Sam conceded that Web Services over TCP is OK too, so I pressed on with:

“What about UDP? FTP? MSMQ? Is it still ‘Web Services’ then? Is the rule then that ‘Web Services’ == SOAP?”

At that point, Sam was beginning to get a little flustered.

“And what’s so great about SOAP? Is it the interoperability? Because that’s just because it’s based on XSD.”

He didn’t know how to reply. Instead, he walked away from the whiteboard and sat down. I didn’t let up:

“And what if we want to do something other than Request/Response? How about one request with many responses? How about many requests and one response? And why does this decision need to be rigid? Shouldn’t we just be able to decide programmatically how many responses we want to return? Wouldn’t that flexibility be better than creating huge response structures for web methods to return?”

image Sam made his last stand:

“Look, we can’t go and do something different from the rest of the industry. Everybody else is doing Web Services. It’s not like the technology doesn’t work.”

I gave way, a little:

“If you want, we can offer two interfaces. One, the flexible, robust, scalable XSD over messaging based solution. The second, an icky, synchronous Web Services facade which calls into our first interface.

I’m not saying that the technology doesn’t work – but both of us know that every problem has multiple solutions, some are fragile and error prone like WS, others are more elegant and have decades of knowledge behind them like messaging.

But we can do both if you like. How’s that?”

image And it was agreed. The entire system would be built on one-way messaging patterns using XSD in cases where interoperability was required. And WS would be layered on, like a tiny little pig on top of a gigantic lipstick … thing – hmm, that metaphor isn’t really working – well, you get the idea.

I hate WSDL. Never been to Vegas, though.

Sundblad Mistaken on Services

Sunday, March 16th, 2008

The brilliant guys at 2xSundbland have launched their architect academy and it looks quite promising. I haven’t yet taken the trial lesson, but its in the queue. I have taken a look at the articles they have on the site as well, and they’re quite good. I especially like the Software Architecture vs. Software Engineering one. There is one topic in that article where I beg to differ, and it’s around services. The article (on page 7) describes the following scenario:

Typically, in such an environment [SOA], services tend to be parts of multiple systems. For example, consider a Products service! It might start its life as part of a sales system. Later it might be involved in a purchasing system, a product development system, a marketing system, a warehousing system, and perhaps in several other systems too. This process may take years, and it really never ends. The service is the same, but its responsibilities and its external exposure are increased with each system it’s enrolled in.

One of the core tenets of SOA that all vendors and analysts agree upon is that there should be loose coupling between services. If you were to design such a product service, it’s clear that changing part of its interface could break almost every system in the enterprise. That doesn’t sound like loose coupling to me.

If there’s one place that is the source of loose coupling – it’s the business. Warehousing is viewed by the business as being fairly independent of Marketing. While Sales might make use of data created in Product Development, business wouldn’t want any problems in IT related to Product Development to inhibit Sales ability to accept orders. That is another kind of loose coupling – the ability of one service to make use of “not-accurate-up-to-the-millisecond” data created by another service. That’s known as loose “temporal” coupling, as in loose coupling in the dimension of time.

Loosely-Coupled Services

So, in the example described we’d see the following services:

  • Sales
  • Purchasing
  • Product Development
  • Marketing
  • Warehousing / Inventory

Product data would flow between the services but each would have a very different internal view of it.

  • Product Development would be more interested in managing the schedule and risk around a product’s development.
  • Marketing would probably be more focused on its relation to competing products and pricing.
  • Purchasing would be maintaining data as to which suppliers are being used to supply raw materials for the production of the product.
  • Sales would be looking at actually accepting orders and giving discounts.
  • Warehousing would be focused on the storage and transportation aspects of the product.

As you can see, there is very little overlap in the data between these services even on something similar like product data. The logic of each service around the management of its data would be even more different. This leads to services with a high level of autonomy.

There Be Dragons…

Without starting at this business-level loose coupling, I doubt that any technical effort will succeed. That is to say every time I’ve seen this style implemented it has failed, but that’s no proof. Conversely, every time that we did start our SOA efforts by identifying the clear business fracture lines, we were able to maintain loose coupling all the way down. That is not to say that it always will succeed, but the logic is sound.

I suppose that the difference between my view on SOA and Sundblad’s stems from the fact that they put systems at a higher level of abstraction than services, and I put services on top. Regardless, I do agree with their views about architecture and engineering and consider them quite valuable.

[Podcast] REST + Messaging = Enterprise Solutions

Sunday, March 16th, 2008

In this podcast we revisit the topic of REST and how to make it work for process-centric enterprise systems. After describing the basic advantages and pitfalls of plain resource thinking, we’ll look at how mapping messaging concepts to resources provides solutions for transactional, multi-resource processing.



Download via the Dr. Dobb’s site

Or download directly here.

Additional References

Want more?

Check out the “Ask Udi” archives.

Got a question?

Send Udi your question to answer on the show.

Interested in SOA Training Videos?

Friday, February 8th, 2008

This past 2 weeks I was in Australia doing some in-depth training on Service Oriented Architecture, Enterprise Development, and nServiceBus implementation. We managed to record one full week of sessions and are in the process of compressing, editing, and other video whatever stuff.

I was wondering if any of my loyal subscribers would be interested in getting a set of DVDs containing Udi talking for hours and hours about how to identify services, map out cross-service business processes, zero in on business fracture points to further decompose services into business components, and decompose those into autonomous components by analyzing non-functional message properties,  summing up with using all that information for choosing cost-effective technologies for each autonomous component.

In other words, get 5 days of training you can pause, think about, and replay as many times as you need. There’s something for almost every phase of an enterprise project, from top level architecture, through coding, testing, to deployment tips and monitoring tactics, so you can pick up what you need – right when you need it.

Please bear with me as I get the processes in place for getting this out.

I’m wondering – how valuable do you think it would be to have weekly live online Q&A sessions as opposed to the more asynchronous (and scalable) simple forum thing?

Just so I can see what I need to be preparing myself for, please leave a comment below expressing your interest. If you also know someone else who might benefit from this, drop them a link. The last thing I want to have happen is for this to take months and months to get out because I didn’t prepare things in advance that I could have.

And a big thanks to Simon and the gang in Australia for helping make this happen. It was a great two weeks and I thank you for that.

Sagas and Unit Testing – Business Process Verification Made Easy

Monday, February 4th, 2008

Sagas have always been designed with unit testing in mind. By keeping them disconnected from any communications or persistence technology, it was my belief that it should be fairly easy to use mock objects to test them. I’ve heard back from projects using nServiceBus this way that they were pleased with their ability to test them, and thought all was well.

Not so.

The other day I sat down to implement and test a non-trivial business process, and the testing was far from easy. Now as developers go, I’m not great, or an expert on unit testing or TDD, but I’m above average. It should not have been this hard. And I tried doing it with Rhino.Mocks, TypeMock, and finally Moq. It seemed like I was in a no-mans-land, between trying to do state-based testing, and setting expectations on the messages being sent (as well as correct values in those messages), nothing flowed.

Until I finally stopped trying to figure out how to test, and focused on what needed to be tested. I mean, it’s not like I was trying to build a generic mocking framework like Daniel.

Here’s an example business process, or actually, part of one, and then we’ll see how that can be tested. By the way, there will be a post coming soon which describes how we go about analysing a system, coming up with these message types, and how these sagas come into being, so stay tuned. Either that, or just come to my tutorial at QCon.

On with the process:

1. When we receive a CreateOrderMessage, whose “Completed” flag is true, we’ll send 2 AuthorizationRequestMessages to internal systems (for managers to authorize the order), one OrderStatusUpdatedMessage to the caller with a status “Received”, and a TimeoutMessage to the TimeoutManager requesting to be notified – so that the process doesn’t get stuck if one or both messages don’t get a response.

2. When we receive the first AuthorizationResponseMessage, we notify the initiator of the Order by sending them a OrderStatusUpdatedMessage with a status “Authorized1”.

3. When we get “timed out” from the TimeoutManager, we check if at least one AuthorizationResponseMessage has arrived, and if so, publish an OrderAcceptedMessage, and notify the initator (again via the OrderStatusUpdatedMessage) this time with a status of “Accepted”.

And here’s the test:

    public class OrderSagaTests 
        private OrderSaga orderSaga = null; 
        private string timeoutAddress; 
        private Saga Saga;     

        public void Setup() 
            timeoutAddress = "timeout"; 
            Saga = Saga.Test(out orderSaga, timeoutAddress); 

        public void OrderProcessingShouldCompleteAfterOneAuthorizationAndOneTimeout() 
            Guid externalOrderId = Guid.NewGuid(); 
            Guid customerId = Guid.NewGuid(); 
            string clientAddress = "client";     

            CreateOrderMessage createOrderMsg = new CreateOrderMessage(); 
            createOrderMsg.OrderId = externalOrderId; 
            createOrderMsg.CustomerId = customerId; 
            createOrderMsg.Products = new List<Guid>(new Guid[] { Guid.NewGuid() }); 
            createOrderMsg.Amounts = new List<float>(new float[] { 10.0F }); 
            createOrderMsg.Completed = true;     

            TimeoutMessage timeoutMessage = null;     

                    delegate(AuthorizeOrderRequestMessage m) 
                        return m.SagaId == orderSaga.Id; 
                    delegate(AuthorizeOrderRequestMessage m) 
                        return m.SagaId == orderSaga.Id; 
                    delegate(string destination, OrderStatusUpdatedMessage m) 
                        return m.OrderId == externalOrderId && destination == clientAddress; 
                    delegate(string destination, TimeoutMessage m) 
                        timeoutMessage = m; 
                        return m.SagaId == orderSaga.Id && destination == timeoutAddress; 
                .When(delegate { orderSaga.Handle(createOrderMsg); });     


            AuthorizeOrderResponseMessage response = new AuthorizeOrderResponseMessage(); 
            response.ManagerId = Guid.NewGuid(); 
            response.Authorized = true; 
            response.SagaId = orderSaga.Id;     

                    delegate(string destination, OrderStatusUpdatedMessage m) 
                        return (destination == clientAddress && 
                                m.OrderId == externalOrderId && 
                                m.Status == OrderStatus.Authorized1); 
                .When(delegate { orderSaga.Handle(response); });     


                    delegate(string destination, OrderStatusUpdatedMessage m) 
                        return (destination == clientAddress && 
                                m.OrderId == externalOrderId && 
                                m.Status == OrderStatus.Accepted); 
                    delegate(OrderAcceptedMessage m) 
                        return (m.CustomerId == customerId); 
                .When(delegate { orderSaga.Timeout(timeoutMessage.State); });     


You might notice that this style is a bit similar to the fluent testing found in Rhino Mocks. That’s not coincidence. It actually makes use of Rhino Mocks internally. The thing that I discovered was that in order to test these sagas, you don’t need to actually see a mocking framework. All you should have to do is express how messages get sent, and under what criteria those messages are valid.

If you’re wondering what the OrderSaga looks like, you can find the code right here. It’s not a complete business process implementation, but its enough to understand how one would look like:

using System; 
using System.Collections.Generic; 
using ExternalOrderMessages; 
using NServiceBus.Saga; 
using NServiceBus; 
using InternalOrderMessages;     

namespace ProcessingLogic 
    public class OrderSaga : ISaga<CreateOrderMessage>, 
        #region config info     

        private IBus bus; 
        public IBus Bus 
            set { this.bus = value; } 

        private Reminder reminder; 
        public Reminder Reminder 
            set { this.reminder = value; } 


        private Guid id; 
        private bool completed; 
        public string clientAddress; 
        public Guid externalOrderId; 
        public int numberOfPendingAuthorizations = 2; 
        public List<CreateOrderMessage> orderItems = new List<CreateOrderMessage>();     

        public void Handle(CreateOrderMessage message) 
            this.clientAddress = this.bus.SourceOfMessageBeingHandled; 
            this.externalOrderId = message.OrderId;     


            if (message.Completed) 
                for (int i = 0; i < this.numberOfPendingAuthorizations; i++) 
                    AuthorizeOrderRequestMessage req = new AuthorizeOrderRequestMessage(); 
                    req.SagaId = this.id; 
                    req.OrderData = orderItems;     



            this.reminder.ExpireIn(message.ProvideBy - DateTime.Now, this, null); 

        public void Timeout(object state) 
            if (this.numberOfPendingAuthorizations <= 1) 

        public Guid Id 
            get { return id; } 
            set { id = value; } 

        public bool Completed 
            get { return completed; } 

        public void Handle(AuthorizeOrderResponseMessage message) 
            if (message.Authorized) 

                if (this.numberOfPendingAuthorizations == 1) 

        public void Handle(CancelOrderMessage message) 


        private void SendUpdate(OrderStatus status) 
            OrderStatusUpdatedMessage update = new OrderStatusUpdatedMessage(); 
            update.OrderId = this.externalOrderId; 
            update.Status = status;     

            this.bus.Send(this.clientAddress, update); 

        private void Complete() 
            this.completed = true;     


            OrderAcceptedMessage accepted = new OrderAcceptedMessage(); 
            accepted.Products = new List<Guid>(this.orderItems.Count); 
            accepted.Amounts = new List<float>(this.orderItems.Count);     

            this.orderItems.ForEach(delegate(CreateOrderMessage m) 
                                            accepted.CustomerId = m.CustomerId; 


All this code is online in the subversion repository under /Samples/Saga.

Questions, comments, and general thoughts are always appreciated.

[Podcast] Message Priority – You Aren’t Gonna Need It

Wednesday, January 30th, 2008

In this podcast we’ll be discussing the issues around supporting different kinds of service-level agreements in an SOA, and how using message prioritization helps and hurts. We’ll also be looking at alternative solutions more distributed in nature,which make use of specific deployment and configuration schemes that result in a more robust system.

Symon asks:

Hi Udi,

I don’t know if this is really an NServiceBus question or a more general architecture question, so if you want to treat it as an Ask Udi question feel free. 🙂  My question is about handling message prioritization between services in an SOA architecture using an ESB-  in this case NServiceBus.

We’ve been running along nicely getting the hang of using the NServiceBus but have just hit a point in our application where it’s become clear that we’re going to need to prioritize messages between services according to an arbitrary set of rules.  To that end we’ve created a “controller” that determines a message’s priority according to a set of rules and that controller should forward the message to other services for handling according to that priority.  Where we’re stuck is figuring out the best way to handle the prioritization of the forwarded message.

We touched on the idea of having several endpoints representing low, medium or high priority and shunting the message to the appropriate endpoint, however since the receiving service consists of multiple workers located on other machines we need to have a dispatcher for each of these endpoints.  Since we’re using MSMQ this seems to be causing an explosion of queues and the solution seems to require a lot of overhead in terms of set up, but it *does* look like it might be flexible as long as we come up with a smart dispatcher.

Is this an “ideal” way to handle message prioritization?  I know there is a notion of priority in MSMQ messages, but this isn’t exposed in NServiceBus as far as I can tell.

Any suggestions?




Download via the Dr. Dobb’s site

Or download directly here.

Additional References

Want more?

Check out the “Ask Udi” archives.

Got a question?

Send Udi your question to answer on the show.

Durable Messaging Is Not Enough

Wednesday, January 9th, 2008

I’ve been sitting on this post for a while, waiting, before outlining all the kinds of problems durable messaging doesn’t solve, I wanted to have a solution handy. Harry Pierson begins to outline the goodness that durable messaging brings to SOA, and in a later post on idempotence describes in general terms how it ties back into durable messaging and transaction – in essence describing a saga. Let’s do this in story form.

Since you’re concerned that maybe your shipping company’s servers may be down for some kind of planned (or unplanned) maintenance just as you’re trying to fulfill orders, you use a durable messaging solution there. What happens is that messages get written to disk on your end, and later the messaging tries to transfer the messages until it succeeds. So what’s wrong with that?

Well, let’s say that the shipping company’s servers went up in smoke (true story – broken down air conditioners + poor ventilation, you get the picture). Those servers aren’t going to be coming back online any second now. So, you have all these order messages buffering on your disk. Taking into account all the data, meta-data, XML, SOAP, encryption and everything, we may get up to 1MB per message.

And now’s holiday season and your company’s selling hand over fist, hundreds of orders per second from all over the world. So that means we’re eating up 100MB of disk per second, that’s 6GB a minute, and in under an hour of our shipping company’s servers going down – so do ours.

Durable messaging – yay? We don’t want to lose those orders, right? In short, durable messaging is an important part of the solution, but it’s not the whole solution.

[Continued next time…]

If you’re impatient and just want the solution, yes, nServiceBus give you all the tools you need.

Israel Grid Technologies Association Presentation on NServiceBus

Tuesday, January 8th, 2008

I know that I’ve been alluding to the grid-like capabilities that are gained when working with nServiceBus, and I’ll be giving a presentation on that next week.

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.


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Bryan Wheeler, Director Platform Development at msnbc.com
Udi Dahan is the real deal.

We brought him on site to give our development staff the 5-day “Advanced Distributed System Design” training. The course profoundly changed our understanding and approach to SOA and distributed systems.

Consider some of the evidence: 1. Months later, developers still make allusions to concepts learned in the course nearly every day 2. One of our developers went home and made her husband (a developer at another company) sign up for the course at a subsequent date/venue 3. Based on what we learned, we’ve made constant improvements to our architecture that have helped us to adapt to our ever changing business domain at scale and speed If you have the opportunity to receive the training, you will make a substantial paradigm shift.

If I were to do the whole thing over again, I’d start the week by playing the clip from the Matrix where Morpheus offers Neo the choice between the red and blue pills. Once you make the intellectual leap, you’ll never look at distributed systems the same way.

Beyond the training, we were able to spend some time with Udi discussing issues unique to our business domain. Because Udi is a rare combination of a big picture thinker and a low level doer, he can quickly hone in on various issues and quickly make good (if not startling) recommendations to help solve tough technical issues.” November 11, 2010

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It was evident through that discussion that Udi is one of the most knowledgeable people in the SOA space. It was also clear why – Udi does not settle for mediocrity, and seeks to fully understand (or define) the logic and principles behind things.
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Udi helped Frequentis to design a major subsystem of a large mission critical system with a nationwide deployment based on NServiceBus. It was impressive to see how he took the initial architecture and turned it upside down leading to a very flexible and scalable yet simple system without knowing the details of the business domain. I highly recommend consulting with Udi when it comes to large scale mission critical systems in any domain.”

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I am honored to have Udi as a colleague and a friend (plus having his cell phone on my speed dial).”

Ward Bell Ward Bell, VP Product Development at IdeaBlade
“Everyone will tell you how smart and knowledgable Udi is ... and they are oh-so-right. Let me add that Udi is a smart LISTENER. He's always calibrating what he has to offer with your needs and your experience ... looking for the fit. He has strongly held views ... and the ability to temper them with the nuances of the situation.
I trust Udi to tell me what I need to hear, even if I don't want to hear it, ... in a way that I can hear it. That's a rare skill to go along with his command and intelligence.”

Eli Brin, Program Manager at RISCO Group
“We hired Udi as a SOA specialist for a large scale project. The development is outsourced to India. SOA is a buzzword used almost for anything today. We wanted to understand what SOA really is, and what is the meaning and practice to develop a SOA based system.
We identified Udi as the one that can put some sense and order in our minds. We started with a private customized SOA training for the entire team in Israel. After that I had several focused sessions regarding our architecture and design.
I will summarize it simply (as he is the software simplist): We are very happy to have Udi in our project. It has a great benefit. We feel good and assured with the knowledge and practice he brings. He doesn’t talk over our heads. We assimilated nServicebus as the ESB of the project. I highly recommend you to bring Udi into your project.”

Catherine Hole Catherine Hole, Senior Project Manager at the Norwegian Health Network
“My colleagues and I have spent five interesting days with Udi - diving into the many aspects of SOA. Udi has shown impressive abilities of understanding organizational challenges, and has brought the business perspective into our way of looking at services. He has an excellent understanding of the many layers from business at the top to the technical infrstructure at the bottom. He is a great listener, and manages to simplify challenges in a way that is understandable both for developers and CEOs, and all the specialists in between.”

Yoel Arnon Yoel Arnon, MSMQ Expert
“Udi has a unique, in depth understanding of service oriented architecture and how it should be used in the real world, combined with excellent presentation skills. I think Udi should be a premier choice for a consultant or architect of distributed systems.”

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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