Udi Dahan   Udi Dahan – The Software Simplist
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The Danger of Centralized Workflows

Wednesday, July 13th, 2011.

It isn’t uncommon for me to have a client or student at one of my courses ask me about some kind of workflow tool. This could be Microsoft Workflow Foundation, BizTalk, K2, or some kind of BPEL/orchestration engine. The question usually revolves around using this tool for all workflows in the system as opposed to the SOA-EDA-style publish/subscribe approach I espouse.

The question

The main touted benefit of these workflow-centric architectures is that we don’t have to change the code of the system in order to change its behavior resulting in ultimate flexibility!

Some of you may have already gone down this path and are shaking your heads remembering how your particular road to hell was paved with the exact same good intentions.

Let me explain why these things tend to go horribly wrong.

What’s behind the curtain

It starts with the very nature of workflow – a flow chart, is procedural in nature. First do this, then that, if this, then that, etc. As we’ve experienced first hand in our industry, procedural programming is fine for smaller problems but isn’t powerful enough to handle larger problems. That’s why we’ve come up with object-oriented programming.

I have yet to see an object-oriented workflow drag-and-drop engine. Yes, it works great for simple demo-ware apps. But if you try to through your most complex and volatile business logic at it, it will become a big tangled ball of spaghetti – just like if you were using text rather than pictures to code it.

And that’s one of the fundamental fallacies about these tools – you are still writing code. The fact that it doesn’t look like the rest of your code doesn’t change that fact. Changing the definition of your workflow in the tool IS changing your code.

On productivity

Sometimes people mention how much more productive it would be to use these tools than to write the code “by hand”. Occasionally I hear about an attempt to have “the business” use these tools to change the workflows themselves – without the involvement of developers (“imagine how much faster we could go without those pesky developers!”).

For those of us who have experienced this first-hand, we know that’s all wrong.

If “the business” is changing the workflows without developer involvement, invariably something breaks, and then they don’t know what to do. They haven’t been trained to think the way that developers have – they don’t really know how to debug. So the developers are brought back in anyway and from that point on, the business is once again giving requirements and the devs are the one implementing it.

Now when it comes to developer productivity, I can tell you that the keyboard is at least 10x more productive than the mouse. I can bang out an if statement in code much faster than draggy-dropping a diamond on the canvas, and two other activities for each side of the clause.

On maintainability

Sometimes the visualization of the workflow is presented as being much more maintainable than “regular code”.

When these workflows get to be to big/nested/reused, it ends up looking like the wiring diagram of an Intel chip (or worse). Check out the following diagram taken from the DailyWTF on a customer friendly system:


The bigger these get, the less maintainable they are.

Now, some would push back on this saying that a method with 10,000 lines of code in it may be just as bad, if not worse. The thing is that these workflow tools guide developers down a path where it is very likely to end up with big, monolithic, procedural, nested code. When working in real code, we know we need to take responsibility for the cleanliness of our code using object-orientation, patterns, etc and refactoring things when they get too messy.

Here is where I’d bring up the SOA/pub-sub approach as an alternative – there is no longer this idea of a centralized anything. You have small pieces of code, each encapsulating a single business responsibility, working in concert with each other – reacting to each others events.

Productivity take 2: testing and version control

If you’re going to take your most complex and volatile business logic and put it into these workflow tools, have you thought about how your going to test it? How do you know that it works correctly? It tends to be VERY difficult to unit-test these kinds of workflows.

When a developer is implementing a change request, how do they know what other workflows might have been broken? Do they have to manually go through each and every scenario in the system to find out? How’s that for productivity?

Assuming something did break and the developer wants to see a diff – what’s different in the new workflow from the old one, what would that look like? When working with a team, the ability to diff and merge code is at the base of the overall team productivity.

What would happen to your team if you couldn’t diff or merge code anymore?
In this day and age, it should be considered irresponsible to develop without these version control basics.

In closing

There are some cases where these tools might make sense, but those tend to be much more rare than you’d expect (and there are usually better alternatives anyway). Regardless, the architectural analysis should start without the assumption of centralized workflow, database, or centralized anything for that matter.

If someone tries to push one of these tools/architectures on you, don’t walk away – run!

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  1. Simon Munro Says:

    Sadly, the same argument can be made against ETL tools (SSIS). Unfortunately ETL visual languages are far more prolific than workflow ones

  2. Pierluigi Says:

    very true. yet the big challenge in loosely coupled distributed systems is to keep track of the inter-dependencies, so as to know where to do code changes whenever a business rule change.
    In my experience we are very bad at that – we still rely too much on PEOPLE remembering the details of the system, rather than a catalog or some automated inventory.

  3. Philip Nelson Says:

    You know, whether the way your business processes are wired together is done in a bpm tool or not, the complexity of what these processes really are, exists. When you don’t put them in a tool, you tend to focus on just the one event at a time, and that does seem simpler: for the developer. But not for the owner of the processes.

    You are absolutely correct about one aspect for most of these tools, they centralize some really basic coding techniques, and a bpm tool is just another notation. I think what will be interesting to watch is if these tools advance as nearly all other notations have that survived, to express more complex branches in a more succinct syntax.

  4. Greger Hagström Says:

    I must recommend Jim Webber (hope I remember his name correctly).

    He has an excellent presentation called Guerilla SOA that pictures this problem perfectly.

  5. Tommaso Caldarola Says:

    If you have to do integration with legacy system an orchestration engine remains one of better solutions because you have to care your side only, so no issue about unit testing as well as version control.

  6. gigiabbrescia Says:

    The listed points are true for all visual tools (also for differents purposes – I hated Oracle Report, Crystal Report, Microstrategy and so on) but will be interesting investegation on pro cons on using a centralized orchestration system (on which I can develop without visual tool limitations) vs pub/sub approch, also in case when I have to “talk” with legacy system.

  7. Jimit Ndiaye Says:

    While I’m a big proponent of the SOA-EDA-style publish/subscribe approach, I don’t think they preclude workflows. I believe the two approaches can coexist. With WF4 for instance, custom activities can be written to interact with a service bus such as NServiceBus, sending commands and listening for events,etc. I’ve found that the visual (bi-directional) communication of intent to business stakeholders provided by workflow technologies can be worth the extra hoops they sometimes force us to jump through. As far the testability story, WF4 does offer a lot more in that respect. While I could probably accomplish the same goals using sagas but for specific scenarios, I like the visual medium that a workflow platform like WF4 provides.

    My 2c

  8. David Nelson Says:

    As usually happens in these discussions, you start out by claiming that centralized workflow is bad, but then try to justify that claim by complaining about the tooling.

    “I have yet to see an object-oriented workflow drag-and-drop engine.” – What if you did?

    “I can tell you that the keyboard is at least 10x more productive than the mouse.” – Who says a centralized workflow engine has to be operated using the mouse?

    “…these workflow tools guide developers down a path where it is very likely to end up with big, monolithic, procedural, nested code.” – There is no reason why a centralized workflow engine couldn’t encourage encapsulation as much as an object-oriented language does.

    “It tends to be VERY difficult to unit-test these kinds of workflows.” – But is that because of the nature of the solution, or the inadequacy of the tools?

    “When working with a team, the ability to diff and merge code is at the base of the overall team productivity.” – Why couldn’t a workflow tool show you graphically where your diffs are and allow you to merge them?

    Integrated development environments, in-depth debuggers, and unit testing suites for mainstream languages didn’t spring up overnight; they have been developed over a long period of time, and they are still developing. That doesn’t mean that the concepts in these languages were invalid until the tools caught up.

    If what you are really arguing is that a decentralized approach is better than a centralized approach because the tools to support a centralized approach are not up to snuff yet, that might be a perfectly valid argument. But then you should approach the discussion from that perspective, and the title of your article should be “The Danger of Centralized Workflow Tools”. Then we could have a reasonable discussion about the pros and cons of centralized over decentralized workflow, without dragging in these ancillary concerns.

    I for one love the concept of centralized workflow, but I won’t use things like Workflow Foundation specifically because the tools are cumbersome and the results are difficult to debug and maintain. But I look forward to the day when the tooling removes those restrictions.

  9. J.D. Says:

    Very scary diagram!

  10. udidahan Says:


    When doing SOA properly, having only one logical publisher for a given event type, there is always only one place where a given piece of functionality/data exists.

  11. udidahan Says:


    Yes, too much business logic gets thrown in those ETL jobs turning them into their own monstrous broker type environments.

  12. udidahan Says:


    I don’t think that I’d agree that the complexity of all processes is inherent – many times I’m able to work with clients and simplify their processes greatly by partitioning them. Other times, we see the process give way to a *policy* which is very well modeled using sagas.

  13. udidahan Says:


    Jim and I see very much eye-to-eye on these matters. He calls these types of tools “visual COBOL” and I think that’s spot on.

  14. udidahan Says:


    You might want to look at my blog post on integration where I describe how to do it without the use of an orchestration engine:


  15. udidahan Says:


    Even if you take the visual parts out of the equation, centralized architectures tend to lead to more monolithic code bases – less maintainable and worse performing than distributed architectures.

  16. udidahan Says:


    Distributed pub/sub architectures don’t preclude workflows, but don’t work with *centralized* workflows. Within each publisher or subscriber, there could be some workflow. It’s been my experience that visual tools don’t help under most circumstances.

  17. udidahan Says:


    On the practical side of things, I’d prefer to use an architecture where the tooling enables me to get things done productively, resulting in high performance and maintainable code.

    If a centralized workflow tool was created that handled all the concerns I raised above, I would evaluate it on its merits.

    Regardless, centralized architectures have proven themselves problematic repeatedly leading us, as an industry, to things like the Single Responsibility Principle – dividing things up so that they don’t all sit in one place.

    Anyway, if you hear of such a tool – ping me. I’d love to take a look.

  18. Charlie Barker Says:

    Managing complexity is the fundamental challenge. If we let any part of our system get into a state of high complexity without putting the neccessary controls in place we end up in a world of pain.
    One of my battle scars was a system that was highly configurable, the problem was this meant administrators were overwhelmed and the task of configuration of all but the simplest of settings was handled by developers. Configuration is harder to test than code so in the end it was a slower and less reliable way of introducing change to the system.

  19. Nuno Lopes Says:

    Humm. I’m not sure if I fully agree with you assessment Udi.

    I know what you mean as I’ve seen horrible things happening with visual tech. These usually started using false premisses:

    1) Workflow IDE are for business people (analysis and so on)
    2) Workflow IDE require minimal to none programming experience

    The fact is:

    1) Workflow Visual Tools are for programmers. They are mainly “code” generators (accelerators)
    2) Workflow Visual Tools require some experience in logic and programing.
    3) They allow analysts to communicate better with programmers and vice versa.

    The problem is that vendors push these products to top level analysts, when indeed they are all about development productivity. This leads to all sorts of problems.

  20. J-F Declercq Says:

    The main underestimated impact of workflows is exception management. If you ask yourself ‘what if somthing goes wrong’ on each worflow step, you’ll maybe understand what I mean. Compensation, roll-back…

    You need to have th possibility to leave the main flow and propose user functions which allow either to put the instance back in the flow or to execute the tasks in a different way…

    Therefore you need to consider the right combination of portal, bpm, bam, rules engines, information management and services in function of each workflow.

  21. tom Says:

    The only motivation I can think of for visualizing code like these tools do, is to have people maintain the logic who do not have the ability to write code.

    I dont see why these tools should be appealing to programmers. For me they have no appeal at all.

  22. udidahan Says:


    I’m sure, at the time, the idea was that people other than developers would be the one doing the configuration. The road to hell is paged with good intentions :)

  23. udidahan Says:


    I’m not sure that I’d agree with the assertion that these visual *programming* tools help business analysts and programmers communicate better. I’d say that verbal communication focused on “what should happen when we don’t get a response from X in T?” will drive out what the real “process” should be.

  24. udidahan Says:


    It’s been my experience that the majority of logic ends up revolving around “exception management”. While it is possible for an experienced developer not to be “duped” by the things that these visual tools make easy, the question is whether those tools are appropriate once you realize the non-sequential nature of the world.

  25. udidahan Says:


    Well, these tools *do* demo well and help convince a CIO to choose one platform over another.

  26. Matt Says:

    I agree the tooling for workflow engines is terrible, but it does not mean the idea is bad.

    The fundamental problem is that modeling the workflow surfaces complexity otherwise hidden until it resurfaces later as bugs or missing features. This makes the problem appear harder than it actually is.

    Modern tooling does not help the matter. Many tools are graphical and sold on the idea that laymen can use them. Trying to represent complex process (a N dimensional graph) graphically (2D) is a very hard problem. Techniques such as AOT or DSM can be used to subdivide the graph into a lower dimensionalities but these are advanced and rare.

    In my experience the most successful workflow engines use Monadic Combinator Libraries. If the domain is narrow enough you can bolt on a DSL / DSM tool on top. And these can finally be made simple enough for a laymen to use them.

    So all you really need is really good developers 😉

    – Matt

  27. verticonaut Says:

    The diagram looks scary – right. What’s missing is the ‘handwritten’ code that would replace it. I’m pretty sure that would look scarry as well! Especially when written by different developers.
    Where I agree is that a workflow tool doesn’t help when a workflow is complex. It will be hard to develop and maintain in either way. And for the rest of the ‘not so conplex’ ones a workflow tool might not be needed at all.
    In large companies, ‘centralized’ and ‘tool or frameworks’ are often considered because they strrugle with inventory and documentation of their workflows. So the decision of using them not really driven by the value of this tools in development – which is limited as you say.

  28. Jerry Bullard Says:

    Apples, meet oranges. You seem to be comparing workflow for everything and code for everything, when in reality each can have a role in your architecture. Nothing prevents us from implementing small, autonomous workflows as publishers and subscribers in a SOA/EDA. Your primary argument then boils down to “monolithic things are bad.” Agreed.

    Also, the notion that “real coders use text” is just silly bigotry. You are ignoring the capability of workflow to be an extensible domain specific language (speaking primarily from the .NET WF4 perspective) with baked in best practices. Ultimately code is code and requires a developer mindset, but we all seek higher levels of abstraction for productivity (or to provide that abstraction to some customer without quite the same level of programming and debugging abilities as we have). You can use workflow to let your customers extend your system while providing the rails and bumpers to keep them from crashing into the walls. Likewise you can use workflow to extend someone else’s system. Beats learning some kind of macro or specialized scripting language.

    Saying it is difficult to write a test for workflows ignores the ability to test each activity in the workflow independently. This is a little like saying it is hard to test a programming language or everything anyone could do with an API. Likewise it is difficult to test a SOA/EDA as a whole. The universe can take on an infinite number of states, so we do our best to test the transitions.

    Finally, not all workflows are simple flow charts. Check out state machine workflows in .NET WF, and you should see a way of managing complexity and visualization of a process out of reach for many, while fitting perfectly in the SOA/EDA ecosystem.

  29. Giscard Says:

    Was going to write some of what Jerry Bullard said.

    And I kind of disagree with the premise of your post.

    “The main touted benefit of these workflow-centric architectures is that we don’t have to change the code of the system in order to change its behavior resulting in ultimate flexibility”

    Pretty sure this is a well known fallacy. The value add as a whole is what sells these products. The designer is a pretty small piece.

    Sadly your post is still a fair caution to many.

  30. udidahan Says:


    I’m willing to agree that what you really need is good developers – they then will be able to decide which tools/techniques should be used where.

  31. udidahan Says:


    I think you hit the nail right on the head – for big complex things, these workflow tools add to the complexity; for small things, those same tools are unnecessary.

  32. udidahan Says:


    Seeing as you agree that centralized/monolithic things are bad, and that many of these tools are evaluated based on that exact usage scenario, I think we’re not that much in disagreement.

    After dividing up a system according to SOA/EDA, one tends to find that most traditional workflows no longer exist, rather they are the result of cascading events from various publishers and subscribers.

    What is left are sagas – a kind of workflow for which some tooling could be helpful. While one area where a tool might be useful is for integration sagas, there are other solutions that tend to be better (like I wrote about here: http://www.udidahan.com/2011/04/08/integration-how-and-where/ ) Another area where sagas are particularly valuable has to do with implementing business policies (a special kind of domain model) and these tend not to be either sequential or necessarily suited to a state machine. A rules engine would be a stronger candidate for a tool, but often the tooling gets in the way of the developer understanding the problem.

  33. udidahan Says:


    Even things which are well known to some need to be repeated for others.

  34. Larry Lynch Says:

    I hate PEGA :)
    we are using PEGA wasting millions of dollars where we could have written code for a week to achieve the same thing with testability, mockability, readability and predictability.

  35. steve Says:

    I agree with the notion of decentralized Sagas especially for business policies – but your link to integration-how-and-where is broken. Have you seen any tools that fit this mold?

    I’ve put FluentWorkflow into production apps and it works extremely well – no underlying tooling/runtime required to make it work. Curious if you have seen others.

  36. Juergen Aschenbrenner Says:

    Good point Jerry Bullard made,… its like the hammer nail problem found in many other problem domains: One has learned to use a hammer and soon every problem looks like a nail.

    I like BPEL and other visual programming tools, because when properly used help gathering requirements from business experts. Same as with mockups when designing the UI.

    The problem with long running batch processes prior to visual tooling, was that there weren’t any artefact’s one could use as a basis to start discussing problems at hand.

    What part of problem domain should be represented visually and what with traditional programming languages should be at the discretion of the developer. Tools like Websphere ID just allow to do that.

  37. Yoni Goldberg Says:

    The business motif: While working with my customers (usually enterprises), I noted that nothing is more important than business agility, my customer understand their business better every day and tends to asks for changes on a regular basis. Sometimes, when code is involved, small changes might be implemented in two weeks or maybe a month, while waiting so long for small changes – the customer loses his patience and belief in the program. Contrarily, when changes are committed really fast, the customers tends to keep asking for changes frequently which makes them see the software as a reflection of their business.

    I believe, especially in enterprises, that nothing drives agility more efficiently than the existing of implementer/power user who works closely to the business user and performs all the changes for him. Workflows tools allow implementer and Power users to change business process rapidly. Code changes involves longer IT procedure for approval: every change requires to make a contact with the IT department (or software vendors), wait for availability, ask the admin for permission to change code on the servers, install on testing servers and more – I see how those procedures exhaust my customers. All the goodies of Workflows agility can live together with robust architecture which handles complexity very well.

    The architecture: Workflows are never meant to handle software complexity. The complex parts, as always, should be encapsulated in software units (for example, DDD entities which are consumed using services), WF activities consume the complex business entities, and then the workflow itself merely an orchestration of software activities which hide the complexity very well.

    After delivering WF activities for the WF system, the implanter can craft multiple different business processes using those activities, He can make changes really fast, change the sequence, change parameters, change HIGH LEVEL if-else conditions and make many other changes. I see at work, how developers code once some software component which then is being used in many different ways by implementers using WF tools. Of course, we cannot change everything using WF tools, sometimes we have to change inside the software entities but it gives a layer of agility.
    So, IMHO, in large systems, workflows are not supposed to be the software itself neither the business logic layer but rather a part of the application layer or facade which consumes software components in techniques that drives agility.

  38. udidahan Says:


    But you’ve got to hand it to PEGA – they’ve made a killing selling these kinds of all-singing-all-dancing tools

  39. udidahan Says:


    I’ve fixed the link. I’ve never used FluentWorkflow but from a quick look at it, don’t like that it makes states so prominent. NServiceBus sagas allow you to use timeouts to “throw state into the future” without having to model it explicitly. These kinds of lightweight solutions often lead to simpler code.

  40. udidahan Says:


    My concern about most of these BPM tools is that they’re usually not very good at representing time, or that they don’t guide the discussion in that direction. In that sense, leaning on a tool to facilitate discussion between IT and business may be counterproductive.

  41. udidahan Says:


    Distributed architectures can greatly facilitate the exact same agility you mentioned by bringing down complexity, enabling to upgrade the system piece by piece, while still maintaining all the robustness and testability of business processes (which ARE logic, no matter what anybody tells you).

  42. Wes Says:

    Amazeballs, best synopsis of this topic yet, thanks!

  43. nightwatch Says:

    It’s great you started a discussion about workflows here, but I’m afraid you jump to conclusions too quick. Probably because you already have the answer for questions not asked yet: NServicebus 😉
    First of all, a BPM engine can and should make use of SOA and services provided by applications and it can make use of a decentralized message bus. Business processes usually go ‘through’ several applications and the software must reflect that by providing the means of coordinated data exchange. You can split the process logic between these applications but without any distinct coordinator you end up with fragmented logic that is difficult to maintain in almost every aspect (versioning, development, production rollout, testing, prototyping, documentation, vendor coordination, …).
    With the right BPM tool you can make a great use of your existing applications and services they provide, my experience is that BPM adds a great value if you can make it work with existing applications/services. The most important benefits, imho, are:
    – versioning: co-existence of multiple process versions is possible
    – easy modfication of process logic, very often without affecting applications involved
    – documentation: process definitions are self-documenting (mostly)
    – common standards for logic description
    – faster development, testing and time to production
    – you can hand more responsibility for the business logic to your client (so they can understand and even modify it without paying the vendor)
    – and many more. Please note I’m not a salesman but rather a software architect with some experience in analyzing and implementing various business processes in telecoms and other big organizations. I’m also an author of a simple BPM engine that proved a very useful tool exactly because of features mentioned above. I agree that real-life process logic is very complicated and building a process description in some modelling language is just programming, not drawing, but please dont try to convince us that you can avoid the complexity by scattering the logic between multiple applications.
    And your last argument about testing,debugging and versioning: why do you think process definitions can’t be versioned or diffed? They are normal text files with structured code/data inside, not GIFs, PDFs or handmade drawings. Testing and debugging is also possible, and can be quite easy if the BPM engine allows you to look inside process state.
    Sorry, I must be going now, hope this subject will be discussed more here.

  44. udidahan Says:


    With regards to your statement:

    “You can split the process logic between these applications but without any distinct coordinator you end up with fragmented logic that is difficult to maintain in almost every aspect…”

    I don’t recommend dividing up this logic between applications but rather between services. Also, in my model of SOA, services aren’t provided by applications. Instead, one can think of an application is a hosting process for pieces of multiple services.

    On your statement:

    “my experience is that BPM adds a great value if you can make it work with existing applications”

    The philosophy of integrating existing applications (without changing them) has been tried before – it’s called Enterprise Application Integration (EAI). This led to spaghetti integration logic implemented in EAI brokers. Now this exact same philosophy is being touted under banners of ESB and BPM. Lipstick on a pig, as far as I’m concerned.

    I would be interested, though, in seeing some examples of a diff/merge process when multiple developers are working on the same set of processes. If you also have an example of a test of a process that calls in/out to various apps, I’d like to see that as well.

    Thanks for your comments!

  45. nightwatch Says:

    I’m trying to continue this discussion but the subject is so broad that I’d have to spend all day writing an answer. So instead I’ll just concentrate on your statements:

    >> I don’t recommend dividing up this logic between applications but
    >> rather between services.
    I fail to see a difference here. In my world applications provide various services from a business perspective but these services are a product of the underlying logic, not the other way round. Maybe you are talking about services built ‘in between’ that provide the logical and technological glue between applications, or the missing parts of process between them?

    >> The philosophy of integrating existing applications (without
    >> changing them) has been tried before
    No, I didn’t say ‘without changing’. Just without adding a logic responsible for something that should be outside the application, like binding to other systems or data transformation required by integration.

    >> I would be interested, though, in seeing some examples of a
    >> diff/merge process when multiple developers are working on the same
    >> set of processes
    I haven’t seen multiple developers work simultaneously on multiple processes. One process is sometimes too much for an IT project. Regarding the technical side, if the process definition language is concise and no automatic code generation tools are used, I see no problem – merge just like ordinary code.
    And spaghetti code imho is the result of not separating the logic of different processes or different versions of the same process – this way the changes accumulate until they obscure all the logic.

    >> If you also have an example of a test of a process that calls
    >> in/out to various apps, I’d like to see that as well.

    My approach to building and testing processes is different. Generally, the IT role in process implementation is to automate otherwise manual tasks. And the automation is a gradual process – you identify most important tasks that need to be automated first and leave the less important to be done later. When building your process definition in a BPM tool you start with all manual tasks, then you make sure the process model is accurate, and then you start replacing them with their automated versions, one by one. The most important thing is that the overall logic and data structures shouldn’t change, you just replace a manual task with its automated version without changing its interface to the rest of the process (by interface I mean input and output data). This way the tasks are completely interchangeable, provided that the interface is kept unchanged. And for testing you can ‘simulate’ any external system with a manual task or a ‘mockup’ code that responds with the same data structure.
    That’s why I said it’s very important that BPM tool allows for easy changes in the process logic

  46. David F Says:

    Hi Udi,

    I think Yoni makes a reasonable point. I agree distributed architecture encourages loosely coupling between components, but my experience showed that distributed architecture can also downgrade the system performance greatly unless using much more expensive hardware solution.

    So, my point is that a proper combination of centralized and distributed architecture should be adopted based on a careful analysis.

    Please correct me if I am wrong.



  47. udidahan Says:


    Well, there’s the first rule of distribution: Don’t.

    So, in some sense, you are correct. That being said, there are ways to analyze business processes so that they can be broken down into more parallel pieces that are triggered off of various events.

    In this model, distribution does provide performance gains as we can have more machines doing more work in parallel, but it would also scale well with more CPU cores on a single box as well.

    Hope that makes sense.

  48. Sandeep Says:

    Though what you say makes some point, I dont see that you know the centralized tools you mentioned use the pub/sub architecture at the core and it depends on us how effectively we utilize it. By going with your approach of writing your own code to create a pub/sub architecure is like reinventing the wheel which someone has already invented. I am not totally convinced with the coding aspect for such scenarios. Instead of writing own pub/sub architecture I think, thinking process should go in how effectively we can use the on the shelf tools available.

  49. udidahan Says:


    I’m not recommending rolling your own pub/sub tooling. What I am saying is that when choosing a tool, look for one that doesn’t lead you to create centralized workflows. NServiceBus is an example of that kind of tooling.

  50. Robert Says:

    First graph looks nice. Much easier to analyse than most ndepend graphs of object oriented projects I’ve worked on.

  51. Gilligan Says:

    I know this is late in coming but, I have been workign at my current company for 4.5 months and when I first came in and saw what they were trying to build I teamed up with the other programmer on the project ot show the boss what a monumental bad idea it was. And the idea was exactly this. It was a workflow engine that they wanted to have a “user-interface”. The boss agreed with us and we quickly scrapped the idea. And we have every day been appreciating how much work that saved us and how cleaner our workflow stuff now looks.

  52. edavis Says:

    Udi –

    I seem to have stumbled upon this topic a little late, but I have a scenario I am trying to wrap my head around. How would you approach a solution for offering multiple, customer-specific workflow possibilities in a multi-tenant system? For example, let’s say you have a default, multi-step, fairly complex workflow defined for the lifecycle of a specific business entity or process, but some of your customers may require a simpler workflow for that same entity or process; i.e. some require approvals, some don’t or maybe they require a more streamlined workflow than your default list of steps. Is there a recommended pattern or approach for offering that type of workflow flexibility and customization?

  53. udidahan Says:


    That’s definitely a bullet dodged. Others aren’t always so lucky.

  54. udidahan Says:


    The advice is to understand that, at a certain point, coders will need to be involved to customize the behavior for customers. The sooner you and the business make your peace with that, you can start to think about creating an ecosystem of partners who will be doing that kind of work while you look to create backwards-compatible APIs at various layers for those partners to leverage.

    See Salesforce and SAP as examples of where this ends up.

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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

Sam Gentile Sam Gentile, Independent WCF & SOA Expert
“Udi, one of the great minds in this area.
A man I respect immensely.”

Ian Robinson Ian Robinson, Principal Consultant at ThoughtWorks
"Your blog and articles have been enormously useful in shaping, testing and refining my own approach to delivering on SOA initiatives over the last few years. Over and against a certain 3-layer-application-architecture-blown-out-to- distributed-proportions school of SOA, your writing, steers a far more valuable course."

Shy Cohen Shy Cohen, Senior Program Manager at Microsoft
“Udi is a world renowned software architect and speaker. I met Udi at a conference that we were both speaking at, and immediately recognized his keen insight and razor-sharp intellect. Our shared passion for SOA and the advancement of its practice launched a discussion that lasted into the small hours of the night.
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.
Humble yet uncompromising, Udi is a pleasure to interact with.”

Glenn Block Glenn Block, Senior Program Manager - WCF at Microsoft
“I have known Udi for many years having attended his workshops and having several personal interactions including working with him when we were building our Composite Application Guidance in patterns & practices. What impresses me about Udi is his deep insight into how to address business problems through sound architecture. Backed by many years of building mission critical real world distributed systems it is no wonder that Udi is the best at what he does. When customers have deep issues with their system design, I point them Udi's way.”

Karl Wannenmacher Karl Wannenmacher, Senior Lead Expert at Frequentis AG
“I have been following Udi’s blog and podcasts since 2007. I’m convinced that he is one of the most knowledgeable and experienced people in the field of SOA, EDA and large scale systems.
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.”

Simon Segal Simon Segal, Independent Consultant
“Udi is one of the outstanding software development minds in the world today, his vast insights into Service Oriented Architectures and Smart Clients in particular are indeed a rare commodity. Udi is also an exceptional teacher and can help lead teams to fall into the pit of success. I would recommend Udi to anyone considering some Architecural guidance and support in their next project.”

Ohad Israeli Ohad Israeli, Chief Architect at Hewlett-Packard, Indigo Division
“When you need a man to do the job Udi is your man! No matter if you are facing near deadline deadlock or at the early stages of your development, if you have a problem Udi is the one who will probably be able to solve it, with his large experience at the industry and his widely horizons of thinking , he is always full of just in place great architectural ideas.
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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