Udi Dahan   Udi Dahan – The Software Simplist
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Race Conditions Don’t Exist

Tuesday, August 31st, 2010.

crossing-the-finish-lineNot in the business world anyway.

The problem is that, as software developers, we’re all too quick to accept them at face value. We don’t question the requirements – in all fairness, it was never our job to do so. We were the ones that implemented them, preferably quickly.

For example

Let’s say we get the requirement the following requirements:

1. If the order was already shipped, don’t let the user cancel the order.
2. If the order was already cancelled, don’t let the user ship the order.

The race condition here is when we have two users who are looking at the same order, which is neither cancelled nor shipped yet, and each submits a command – one to ship the order, the other to cancel it.

In these cases, the code is simple – just an if statement before performing the relevant command.

So what’s the problem

A microsecond difference in timing shouldn’t make a difference to core business behaviors. Which means that we’ve actually got here is a bug in the requirements. Users are actually dictating solutions here rather than requirements.

Let’s ask our stakeholders, “why shouldn’t we let users cancel a shipped order? I mean, the users don’t want the products.”

And the stakeholders would respond with something like, “well, we don’t want to refund the user’s money then. Or, at least, not all their money. Well, maybe if they return the products in their original packaging, *then* we could give a full refund.”

And as we drilled deeper, “when do refunds need to be given? Right away, in the same transaction?”

The stakeholders would explain, “no, refunds don’t need to be given right away.”

It turns out we were missing the concept of a refund, as well as assuming that all things needed to be processed and enforced immediately. Once we dug into the requirements, we found that there is actually plenty of time to allow both transactions to go through. We just need to add some checks during shipping’s long-running process to see if the order was cancelled, and then to cut the process short.

So is everything a long-running process then?

That’s actually a fair question – long-running processes are a lot more common than at first appears.

What we’re seeing is that cancellation is now a command that has no reason to fail – just like CQRS tells us. When this command is performed, it publishes the OrderCancelled event, which the billing service subscribes to.

Billing then starts a long-running process (a saga, in NServiceBus lingo), also listening to events from the shipping process, ultimately making a decision when a refund should be given, and for how much.

Deeper business analysis

As we discuss matters more with our business stakeholders, we hear that most orders are actually cancelled within an hour of being submitted. It is quite rare for orders to be cancelled days later.

In which case, we could look at modeling the acceptance of an order as a long-running process itself.

When a user places an order, we don’t immediately publish an event indicating the acceptance of an order, instead a saga is kicked off – which opens up a timeout for an hour later. If a cancellation command arrives during that period of time, the user gets a full refund (seeing as we didn’t charge anything since billing didn’t get the accepted event to begin with), and the saga just shuts itself down. If the timeout occurs an hour later, and the saga didn’t get a cancel command, then the order is actually accepted and the event is published.

Yes, sagas are everywhere, once you learn to see with business eyes, and no race conditions are left.

In closing

Any time you see requirements that indicate a race condition, dig deeper.

What you’re likely to find are some additional business concepts as well as the introduction of time and the creation of long-running business processes. The implementation at that point will pivot from being trivial if-statements to being richer sagas.

Keep an eye out.

  
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35 Comments

  1. Jean-Jacques Dubray Says:

    Udi,

    if I may, I think you have just discovered the concept of “business entity lifecycle” (which now even has a spec BEDL). There is a simple implementation model underlying BELs: namely orchestration. Orchestration languages could be semantically a bit richer, but they do the job, they serialize incoming messages (events or action requests) and decide whether the Business Entity is in a state where an event can be consumed or an action executed.

    It is kind of sad that in 2010 the dominant model is still RPC and now REST pushes it down a notch to the CRUD level.

    I have taught several IT organizations how to model their processes, not as a flow, but as a series of business entity lifecycles interacting with each other. This is the kinds of things I described in WSPER many years ago: http://www.ebpml.org/wsper/wsper/wsper_primer.pdf

    JJ-


  2. udidahan Says:

    JJ,

    The issue that we have in our industry is not in the solution domain, but rather how we interpret requirements. Many developers do not know enough about requirements engineering so we need to provide rules-of-thumb to help them pick up on solutions masquerading as requirements. That was ultimately the point of this post – not to prescribe any kind of solution for these cases.


  3. Alex Simkin Says:

    “A microsecond difference in timing shouldn’t make a difference to core business behaviors.” But it does. And we have precisely the same situaltion here.
    – The order considered shipped when the box scanned at shipping station. After that it can sit in the warehouse for days awaiting truck but it cannot be cancelled as it is too expensive to go and search for the box. From this moment customer can only return order back (Return is different from Cancel because customer will be charged for shipping and re-stocking).
    – If however order was cancelled one microsecond before it was scanned, the shipping station rejects the box and it will be re-stocked free of charge.


  4. Nuno Lopes Says:

    “The issue that we have in our industry is not in the solution domain, but rather how we interpret requirements. Many developers do not know enough about requirements engineering so we need to provide rules-of-thumb to help them pick up on solutions masquerading as requirements.” – Udi

    Agreed.

    Considering the example a point against is that the “refund policy” is not to take care of race conditions. You might even have the case that only Orders bellow over certain amount are entitled to refunds (business cost efficiency). What happens then? Is the user forced to pay an order that has been cancelled? … If we proceed with this probably but not very nice.

    It is true that in the business world there are little race conditions but this is driven to the physical nature of the medium (paper).

    How? Well In the business world we don’t have two users editing an order simultaneously, so allowing that to happen is was for sure a technical decision. In the business world would be two users reaching for the same Order (paper), then they would say – you take it, no you take it oh, ok thanks.

    So this particular race condition is not created by the business, but the medium, computers.

    The down the rabbits hole the race condition described here is that indeed we have two users reaching out the same Order at the same time to change it yet with no inter communication. So this needs to be mediated in a different way. This can be considered a technical problem derived from the context (computers).

    All in all, to fully avoid this race condition the business process needs to be reengineered with the business people.

    I think that is probably the core point of this article.

    Nuno
    PS: Probably an implementation more closer to the business would be for the user to check out the order, change it and submit it. This could be managed with a Saga in a transparent way as far as I understand it. But then again we could have a race condition when checking out.


  5. David Nelson Says:

    I agree with Alex. You haven’t eliminated the race condition, you have just moved it to a different point in time.

    While I agree that on the whole the software industry does a poor job of requirements gathering, I don’t see how that in any way changes the logical concept of a race condition.


  6. udidahan Says:

    Alex,

    The bottom line of the customer not wanting the products doesn’t change because of a microsecond. The ultimate question is how much of a refund does the customer get, and when.

    Since the customer doesn’t know if the order is about to be scanned at the shipping station, why should the system care? Also, shouldn’t the company be concerned about restocking costs regardless of the microsecond? Can’t we just raise the cost of cancellation and be done with it?

    The requirements you’ve presented assume a 100% consistent system, and that has severe scalability and availability costs related to it – those should be balanced with all of the above as well.

    The goal is for our system (as a whole) to be profitable, and give a good user experience as well. Fairness and timing aren’t necessary to fulfill those goals.


  7. udidahan Says:

    Nuno,

    ” to fully avoid this race condition the business process needs to be reengineered with the business people”

    Agreed.


  8. udidahan Says:

    David,

    See my answer to Alex above.


  9. Alex Simkin Says:

    @udidahan

    You are describing an attempt to hide a system defect with additional charges passed to the client.

    We solved it by implementing “standard” locking mechanism that you would use to avoid race conditions when accessing any shared resource. If customer calls about a specific order number, lock this order if not yet shipped (race condition possible), then check again that it is not shipped and inform the customer if it is too late (or not) to cancel the order.


  10. udidahan Says:

    Alex,

    I can see that your opinion is that software should implement the requirements, regardless of what those requirements are. If the requirements demand for the system to have a centralized locking mechanism, then your position is to build it that way.

    My position is that those are not requirements, but rather dictated solutions. What I need from the business is their goals, objectives, and scenarios they want to support – not requirements (it’s not their job to come up with those). Then (wearing by business analyst hat), I work with the business stakeholders to formulate the requirements that address the above *without* requiring synchronous locking across business-capability boundaries (shipping and sales are different).

    When the business signs off on these requirements, the behavior of the resulting system is correct by definition – we’re not hiding a system defect.

    I think we’re looking at things from different perspectives, me in the form of re-engineering the requirements, and you from the implementation of the original requirements.


  11. Neil Mosafi Says:

    “If the timeout occurs an hour later, and the saga didn’t get a cancel command, then the order is actually accepted and the event is published.”

    But what happens if a cancellation is received just after the timeout occur? Surely we’ve just moved the race condition from “order shipping + order cancelled” to “timeout occurs + order cancelled”?


  12. udidahan Says:

    Neil,

    First of all, preventing a large percentage of these occurrences is already a big win – applying the 80/20 rule here. Second, as I said in the post, the handling of the apparent race conditions has to do with deciding *later* how much of a refund to give the customer, rather than trying to block one of the users from performing an action.


  13. David Nelson Says:

    Udi,

    I cannot tell you how envious I am that you have never had to build an application based on dictated requirements. Can you tell me your secret?

    In this case, why are you assuming that the business has just overlooked the possibility of offering a smaller refund after the product has shipped? How do you know that they have not considered that possibility and rejected it for valid business reasons? You are trying to wave a magic wand and make the race conditions go away, but the real world doesn’t work like that. Sometimes race conditions DO exist.


  14. udidahan Says:

    David,

    My secret is that companies have tried doing things the way they’ve always done them and ended up stuck – either in terms of scalability, complexity, time to market, etc. By the time they come to me, they’re ready to listen and understand how related all these things are to each other.

    The reason that I’m assuming that the business *has* overlooked these possibilities is that they *don’t* know the costs of synchronous centralized system. The business assumes (not in the least because we techies told them so) that no matter the requirements, we’ll be able to build it in a scalable manner. It is *our* assumptions, as technical people, that need to be adjusted – and then communicated back out to our business stakeholders.


  15. Milo Says:

    Udi,

    Is there not still a point somewhere in the timeline of an order beyond which cancellation is not allowed?


  16. udidahan Says:

    Milo,

    That’s a business question – ultimately the question is why? If the customer is required to return products in original packaging to get a refund (where the refund may not include shipping costs), is there any risk?


  17. Milo Says:

    Udi,

    I think there may be a terminology issue here. Returning a product in original packaging is not canceling an order, it’s returning a product. These are two different things. Now it may be that you feel the distinction is unimportant. It could be argued that both processes are simply solutions to the more general problem of a customer no longer wanting something they previously ordered. Is that what you’re advocating, that the requirements derive from this higher-level idea?


  18. udidahan Says:

    Milo,

    Agreed, the customer has to explicitly express their intent to cancel the order. Yet, when it comes to refunds, those are influenced by whether the products are returned (or can be returned in the case of digital/virtual products) and in what state they were returned.


  19. Milo Says:

    Udi,

    If they explicitly request cancellation, the outcome depends on whether or not the order can be canceled. More generally, if someone requests X, the outcome of that request depends on whether X can occur. If there is a point at which that possibility changes, then there is the potential for a race between that transition the request.


  20. Kyle Szklenski Says:

    “Race conditions do exist! What about a racing app?” – just made up, but sounds like some of the funny responses you get at times, Udi. :)

    I’m really glad you’re preaching for the DDD lately. What you’ve written is a very DDD way of handling the solution, in my opinion.

    The way I’ve said the above before was: There are almost *no* new business concepts in modern day programming. Almost everything you could write has been written before. Instead of requiring all new code, study up some on the business domain and eventually become a kind of expert on it. Then, implement the solution.

    To be perfectly honest, though, most of the projects that I see that have race conditions only exist because the coders were so confused about what multi-threading is meant to solve.


  21. udidahan Says:

    Milo,

    It looks like we’ve come full circle – see my posts about CQRS and why commands should succeed.


  22. udidahan Says:

    Kyle,

    Glad you liked it. As an industry, I think we need a bigger focus on business analysis than technical/technological approaches.


  23. Harald M. Says:

    Late to this discussion, I risk adding a quite high-level comment:

    Even though I have preached Udi’s arguments for some time, there is a (in my experience) huge psychological downside to this type of arguments and, especially, the behavior that follows from it: The “software people” start occupying (or are seen to do that) more and more “business territory”, and – being convinced that they are the better analysts – they start decreeing how the business goals should be set up to produce the “right” requirements (and then software).

    Arguments and utterances of the form “you should not tell me … because you dicate a solution …” are amiss of the necessary humbleness when different people and different cultures (like “business” and “software”) have to work together for a long time in a company [consultants that leave projects after less than a few years(!) often ignore such effects … and I say that having been such a consultant for 10 years].

    Creating new business processes often works only by trying out concrete solutions in discussions. Thus, the question “Why can’t you simply put a pessimistic lock on that?” is *legitimate* by a business person who has had a mutual understanding with well-communicating software colleagues for years; the answer is *not* “Not your territory”, but getting mutual understanding of the costs and benefits also of this sort of low level solution ideas.

    On the whole, the group process of redefining the processes and requirements to possibly introduce an alternate business process needs lots of tact.

    *If* this tact is present in (almost) *all* the stakeholders and participants of that defining process, then what Udi describes is the best of all worlds.
    *If* it is *not* present – and in my experience of more than 25 years, quite often there is that one person among the 10 or so participants who doesn’t have it, it is on the whole better to *not* go into such discussions. Especially and as we all know (? – :-)), some “high power developers” have an astonishing and sometimes enormous lack of the subtle social skills necessary to handle “territorial” aspects; i.e., they like to formulate the “don’t give me solutions – just let me decide what’s right here” in a way that can poison collaboration for years.

    This text is not watertightly structured and perfectly argued – the idea is rather to get across doubts about the conceitedness that we, as the “masters of analysis, design and everything,” radiate …

    Harald M.


  24. udidahan Says:

    Harald,

    I think that you’ll agree with me that there is a middle ground, and although the pendulum might swing a little too far back, it is part of a maturation process that we should not fear to start, even though we know we’ll stumble along the way.


  25. Henry Says:

    You make it sound like your business people will say “ah thank you for your brilliant business thinking, we hadn’t thought of that”.
    The conversation will more likely go like:
    Them: “why do you have to make everything so difficult?”
    You: “Microsecond blah blah, customers dont care blah blah, costly to implement blah blah”
    Them: “What happens to the simple atomic ‘update where shipped=0′”?
    You: “Scalability blah blah, high volume blah blah”
    Them: “Our young freshman dev wrote this in less than 5 minutes, easily handles 50k atomic updates like this per second on a single mongodb instance, no sweat broken so far. That’s 50k cancellation requests per second, for crying out loud! So if you can’t even handle 3 cancellation requests per hour *correctly*, I’m sure we won’t have any problem finding someone who can”


  26. udidahan Says:

    Henry,

    Well, it’s unlikely that business people will be talking to techies about the throughput of mongodb, nor are they in a position to judge whether the consistency guarantees are enough for their needs.

    I can say that business people tend to tell me, “yeah, that’s what I meant all along” when I go down this path with them. YMMV.


  27. Watch out for superficial invariants Says:

    […] as you’ve probably heard me say before, you end up with sagas as your aggregate roots (see Race conditions don’t exist from 4 years […]


  28. udaya Says:

    Consider this scenario:
    1 seat available for taking on a plane including overbooking limits.
    Two customers want to book in on same microsecond. Only one should get it.

    how will this be solved without locks and race conditions?


  29. udidahan Says:

    Udaya,

    That’s why things like waiting lists were created.


  30. udaya Says:

    yes Udi. I understand. what if this is the last seat in the waiting list?
    There is always a point beyond which we cannot postpone the decision and race will occur.

    Or please let know if I am missing something.


  31. udidahan Says:

    Udaya,

    Think about how a human being might handle the scenario, for example, booking them on the next available flight to that destination.


  32. Not a techy Says:

    Isn’t it easier to queue the ‘ship’ instruction and then after a given lapse of time look for a ‘cancel’ status on the order, if not cancelled, then proceed to ship. Once the ship instruction has been activated the order status changes to ‘shipped’


  33. Uardum Says:

    Udidahan, booking on the next available flight doesn’t get rid of the race condition. To put one of them on the next available flight, the software must first realize that two people are trying to book the same seat on the same plane! That’s where the race condition happens.

    If the race condition is simply ignored, then two people will eventually show up to the airport with tickets to the same seat, and one of them will end up staying behind, while their luggage gets flown away.

    That passenger will choose a different airline next time, and will make sure that everybody he knows does the same, even if you belatedly re-book him on the next available flight after he shows up for boarding.


  34. udidahan Says:

    Not a techy,

    Queuing the ‘ship’ instruction just moves the theoretical race condition to after the lapse of time.


  35. udidahan Says:

    Uardum,

    Yes, when software is managing a real-world limited inventory, it does need to be designed to handle that – and that means surfacing those constraints appropriately in the UI. A big part of handling race conditions well involves creating long-running processes so things don’t just fail.


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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.”

Consult with Udi

Guest Authored Books
Chapter: Introduction to SOA    Article: The Enterprise Service Bus and Your SOA

97 Things Every Software Architect Should Know



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