Udi Dahan   Udi Dahan – The Software Simplist
Enterprise Development Expert & SOA Specialist
    Blog Consulting Training Articles Speaking About

Archive for the ‘Autonomous Services’ Category

Tasks and Spaces versus Messages and Handlers

Thursday, May 10th, 2007

While going through the JavaSpace presentation I found on Owen Taylor’s blog, I kept saying to myself, “well, I can do that without a space”, until I got to one part of it.

The ability to introduce a new task at runtime without restarting any servers, and have new clients be able to send those tasks, and existing servers perform them. I never did that before.

This is very important when you’ve already got a system running and you want to expand on it. I think that this covers at least half of all the software work being done on the planet.

The interesting thing is that this ability comes in two parts – one design, the other technology.

In terms of design, in order for existing servers to be able to do the work of the new task without any kind of restart, we need the code for performing the work of the task to reside in the task itself, possibly in some kind of “execute” method. The server would simply take a task out of the “queue” of pending tasks and call that execute method.

Now, those of us trying to do this with Microsoft technology know that if the assembly containing the code for that task was not available on that machine, this wouldn’t work. Technologically speaking, we’d receive some kind of deserialization exception that resulted from a TypeNotFoundException. In other words, in order to support the new task, we’d need to “install” all of its participating assemblies on all our servers.

For those of us who know and use Jini with Java, we get this behavior automatically – the bytecode of the task is downloaded automatically. This is an advantage in terms of operations, but I’m not an operations guy so I can’t say how huge this really is.

The interesting thing for me in this design is that it’s somewhat different from the messaging paradigm I’ve been so successful with. Here we don’t use messages as simple Data Transfer Objects. Tasks contain both data and behavior. This behavior used to belong to message handlers. I like having separate message handlers, it enables me to create very flexible pipelines.

Here’s how I’d trade it off. When using Jini, the tasks style gives me zero footprint deployment. When using .NET, if I’m already installing things on my existing servers, I can deploy new messages and handlers just as well as the task assemblies. The problem is that I’d need some way for the server to pick up on the new handlers – a background thread scanning the deployment directory, or the FileSystemWatcher (given the fact that it sometimes misses things).

Well, it looks like both design styles are feasible on both platforms. The ability to have code download automatically on the Java platform is a plus that is most felt when using tasks.

Bottom line so far, there’s a lot to learn from JavaSpaces, and even if you don’t use Java, Jini, or Space technologies (like this), the design patterns employed there are extremely valuable.

Using spaces with web services

Saturday, May 5th, 2007

Willam Brogden has an article up on SearchWebServices.com on How Web Services can use JavaSpaces. I don’t want all the Microsoft folks tuning out now that they’ve heard the “J” word, so let me just say that there are technologies out there for .NET too.

A “JavaSpace” is really just a space, which is, at the end of the day, a queryable distributed in-memory hashtable. Something many of us are already doing for caching. The reason you shouldn’t be doing this yourself is simple. While keeping a single hashtable in memory on a single computer and synchronizing it against changes to your database is simple, doing that in a highly available manner across multiple servers is not. Vendors providing solutions in this space include:

But there are others as well. Bottom line: don’t develop one of your own. Do a proof of concept with your short list of vendors and go from there.

The article sums it up nicely like this:

Although JavaSpaces servers are not trivial to set up, they are much easier than any other type of grid computing server. Furthermore, the simplicity of the interface makes the learning curve easier. The greatest advantage of the JavaSpaces approach is the ease with which additional workers can be added to the grid.

It should be clear from the example that there is a lot of extra communication traffic in a JavaSpaces solution so the only reason to use JavaSpaces or any other form of grid computing in support of a Web service is a requirement for computing power or special resources that are not feasible to supply on the server directly.

I have this to add to it. Whereas most traditional systems keep the idea of message-based communication and data caching separate, spaces allow you to kill two birds with one stone. Even if you don’t go the whole Space-Based Architecture route, you’ll find that spaces will fit nicely in your distributed architecture toolkit – I know I did.

SOA, Service Broker, and Data

Friday, May 4th, 2007

Roger Wolter, who is trying to evangelize the architectural aspects of data in SOA, has this to say:

After all, you don’t have to go too far down the SOA path before you realize that unless you build reliable, asynchronous, loosely-coupled services, your SOA architecture is going to have serious reliability problems and Service Broker brought reliable, transactional messaging to a whole new level of reliability and efficiency. What I found was a bunch of architects trying to figure out how to use WS-Transactions to build tightly coupled services to replace their tightly coupled objects.

So far, I’m thrilled that he is pushing this message in, and out of, Microsoft.

He then goes on to debunk the idea of Entity Services:

I next ran into a lot of people architecting SOA systems to provide a common services interface to a lot of diverse back-end systems. I’ve talked to people who had over 100 systems that handle customer data for example. If you build a perfect customer service to wrap all these systems with a common schema for the customer record you have a single view of the customer right? The first time your user tries to change the phone number for Acme Rockets Inc. and gets back 80 records which may or may not be for the same customer, the single view of the customer loses some of its appeal.

I’m loving it.

He then suggests a solution:

That’s how I got interested in Master Data Management. I really believe that accurate, unambiguous clean data is a prerequisite to an SOA project.

Hmm, from what I’ve seen of MDM, it puts a different spin on all the other things he said above.

Other than that, I’m totally with him. A deep understanding of data is necessary to get a good service decomposition. Without understanding the transactional nature of that data, you just might end up back tightly coupled and with a monolithic web service mess.

Whether or not you use Microsoft’s SQL Server Service Broker, Roger is definitely a guy worth listening to.

Does REST simplify communication more than SOA?

Tuesday, May 1st, 2007

From a somewhat old email discussion I had with Benjamin Carlyle:

> A while ago I tried to explain the difference between SOA and REST is
> that SOA is based on “MEST” – MESsage Transfer. The main thing is the
> message – which is a statement of intent, and includes the relevant
> data for that intent. For instance, a message like
> ChangeCustomerAddressMessage is itself the intent; the data it
> carries, the customer ID and the new address completes the picture.

Ahh. This puts your name in context for me. I did some reading on MEST some time ago. I think that there are probably a few misunderstandings on both sides of the fence still about what the other is all about. I have recently been reading “Software Factories”, ISBN 0-471-20284-3. It takes the view of a service being a software component. Code usable in different software environments that has enough self-description to be accessed from multiple languages and runtimes. This sets up services as platform-independent objects.

I think I understand this evolution and the corresponding object patters that are encoded into WS standards. Essentially, SOA attempts to make objects more accessible. REST is quite a different beast. Its primary function is to allow communication to evolve.

> The main difference between this style and REST is that where REST is
> focusing on one resource, SOA/MEST style accept that fact that as a
> result in the change of address, the customer may now be in a “rich
> neighbourhood”, and his customer rep now has over X people in rich
> neighborhoods, so the customer rep’s status changes. This cascading of
> changes I believe is done in orchestration/choreography type code outside of the resource in REST.
> Such complex business logic is best implemented using OO models which
> span objects/entities/resources.

I think this is a common misunderstanding. Each resource demarcates a subset of an application’s state. Resources are likely to overlap. When one resource is updated, it is likely that other resources will also change. This is not well ennunciated by REST proponents who are far more focused on the other side of the exchange, that between client and server. In REST, your ChangeCustomerAddressMessage sent to object A would be a PUT of a customer address record over the top of the old one, at resource http://example.com/customer1.

I see REST as a tweak to the object model. Instead of having a base-class that defines methods and data to be transferred, REST decouples the definition of methods and data. The intention is that the set of methods, the set of data definitions, and the set of objects
(resources) can evolve independently of each other. This tweak does not change existing capabilities of the object model. Objects work pretty-much as before, but their interface to clients and the definition of their interface is modified.

The effect of the decoupling is that methods can be understood separately to data and to objects. For example, I can determine what a GET or PUT request is going to do to a resource regardless of the object the method is applied to. As an intermediatary I can operate as a caching proxy, or apply security policy appropriately. I see this like the jump to java beans. Some programmers were downright offended that they had to name their methods with “get” and “set” in order to get the architecture working, however the advantages are now so clear that the issue simply doesn’t come up anymore.

REST is about building a communicatons infrastructure that scales to a large number of participants who want different things from their architecture over time. At a technical level there are significant performance advantages to be gained by caching and other features, but at a social level it makes the definition of new interfaces simpler and allows them to change over time without disrupting the architecture as a whole. New methods can be introduced over time. New content types can be introduced over time. Old features can be supported simultaneously to new.

> It is this model of message/document based communication that isn’t
> very well supported by WSDL. Support for publish/subscribe semantics
> is also vary light in the WS world. This is the main reason why I see
> SOA as something outside of WS. I don’t see this as a “nod” to REST
> but a coherent architectural style that been employed long before the web.

Support for pub/sub is also pretty light in the REST world, something I have mind to do something about 🙂

> As for scalability, it’s very easy to scale the publishing of static
> html pages, it is an entire other thing to scale complex business
> logic that may have huge working sets of data. To tell you the truth,
> I’d be interested in seeing the design of such a system in terms of
> REST, specifically in how transactions are handled.

Transactions in REST are usually handled by demarcating all of the state that will be updated in a single resource, and PUTting a representation of that state to the resource. REST is usually applied at a chunky enough level that this makes sense. There is always the expectation in REST that objects or RDBMS or some other back-end technology does the work of making the updates.

There are other ways to handle transactions in REST, but they usually don’t come up. Again, it is a matter of scale and the level of abstraction. REST is a client-facing communications model. It isn’t necessarily useful for communication between services within the same tier. It may also be that the tier that presents a REST world view hides further tiers that use distributed object technologies.

> Anyway, that’s where I’m coming from. I think that the communications
> semantics of SOA – send a message, are just about as simple as it
> gets. It is, if anything, more minimalistic than REST.

I think that you are right about minimalism, at least after a fashion.
With WS-* or even corba, it is easy enough to make two programs work like one in an enclosed environment. REST is really about a larger-scale communications system where not all of the participants are part of the same organisation. It is about forging agreement on the larger scale, not an easy thing to do. However, I think that REST scales down better than SOA scales up. It is no harder to define special-purpose XML formats than it is to define a base-class, although defining all appropriate resources is probably starting to make life too difficult.

My organisation integrates disparate systems. It is about 50% of the work we do on a job. In this environment REST is a valuable tool in making things work with each other over long periods of time, and exposing the data of one system to another for viewing and update.

Orignal message:
> I’m quite interested in expanding my knowledge of SOA best practices.
> As I noted in the entry you refer to that my list is derived from a
> presentation by Sun Microsystems, the slides of which may be found href=”http://au.sun.com/events/developer/downloads/download.html?s_dLi
> nk=SOA _JBI_BPEL.pdf”>here
. I often hear that SOA is an
> architectural style rather than a name for the WS-* stack, however it
> is hard to come to terms with what those principles are given the
> variety of views on the subject.
> It seems that many SOA proponents who are familiar with REST take a
> number of their particular constraints from REST itself. If those
> individuals are to be taken as the litmus test, SOA is generally a
> superset of REST that allows for less uniformity. In other words it
> looks like a version of REST that doesn’t scale up to such big network
> sizes. Vendors seem to see SOA differently, the message-bus focus I
> referred to in my entry.
> I would also like to note that the main focus of the title was on the
> principle difference that I percieve there to be between SOA and REST:
> the nature of the uniform interface. Even if you take your web
> services and try to construct a uniform interface, you do so as a
> base-class that encapsulates both verbs and content types. REST
> decouples these. I think the same is possible as document-oriented
> processing under web servcies, however this again seems to be a nod to
> REST rather than an alternative to REST practice.
> Do you have a specific list of constrains you yourself like to point
> to as the meaning of SOA?

[Podcast] Message Schemas Between Multiple Publishers and Subscribers

Monday, April 30th, 2007

This week’s question comes from Bill who asks:

Thanks again Udi for your informative response. I have been having more and more continued success leveraging service oriented design principals in my work. My client is thrilled with the result – systems that work and are agile! 🙂 Your advice over the last number of months has been a big ingredient in that success.

As per usual, I have another question I was hoping I could trouble you with. I have a service which needs to subscribe to a topic which is a parent topic in a topic hierarchy.

Say I have 3 different families of insurance products, each of which have a “Policy Written” event. So we would have:

Product Family 1 Policy Written
Product Family 2 Policy Written
Product Family 3 Policy Written

These 3 messages have some information in common – such as Policy Number, Product Code, Date Written, etc. I’d like to be able to add more products with their own unique “Policy Written” event, without altering the service subscribing to the “Policy Written” topics. This means that the subscribing service would need to know about the “Policy Written” base type of message, without knowing about the specific sub types. Assuming the messages are serialised using SOAP/XML, would you recommend achieving his using XML data type inheritance? So each of the message sub types would inherit from a message base type? Or would you recommend just having the subscribing service understand each message sub type, and update it as new sub types are added? Or is there another solution you could offer?

I can see that having the base message type increases coupling between publishing services because each service that publishes a Policy Written event must adhere to the base message type schema. But I can also see having the subscribing service understand all message sub types increases coupling between the subscribing service and the publishing services because adding a new insurance product requires modifying the subscribing service to understand the new message sub type.


Get it via the Dr. Dobb’s site here.

Or download directly here.

Additional References:

Podcast on Autonomous Services and Pub/Sub
Podcast on Business and Autonomous Components in SOA

Want more? Go to the “Ask Udi” archives.

Service Component Architecture, Service Data Objects, and my bus

Monday, April 30th, 2007

There’s been quite a flurry of activity around Service Component Architecture (SCA) and Service Data Objects (SDO) in the non-Microsoft community. These specs have been sent for OASIS ratification and have garnered support from the Open Service Oriented Architecture (OSOA) organization – a collaboration of a dozen top software vendors including IBM.

I’ve been getting some questions on how these upcoming standards correspond to what I’ve been describing about SOA. Specifically, how does SCA relate to the Business Components and Autonomous Components I podcasted about.

First of all, I’d say that the SDO thing is, in my opinion, “much ado about nothing”. These are “merely” the messages that are sent between services. We don’t need further standardization there, if the WS-Splat has taught us anything it’s that more is definitely not better.

In terms of SCA, it’s components seem to correspond to the Service Layer of an Autonomous Component.

What does all this have to do with Web Services? Well, in both the SCA/SDO case and in my ESB/SOA case, we add constraints and guidelines on top of the generic ways WSDL has been mangled by the tooling.

In all cases, we still need to discuss what makes a good contract – what is good message design. I’ll be dealing with that in the next coming days.

More information:

Info from IBM on SCA.
Info from IBM on SDO.

The Enterprise Service Bus and Your SOA

Saturday, April 28th, 2007

It was about a year or so back—I was in the middle of figuring out how to pass an authorization token between trust boundaries when I got a call from our CIO. He had just come back from some conference sponsored by *** (Vendor’s name withheld to protect the clueless) and was brimming with new acronyms.

“Udi”, he says, “I just heard that for us to realize the potential of our SOA, we should be using an ESB.”

I’m sure he said a lot more than that, but that first sentence was enough for me to tune out. I managed to get through the conversation without catching a case of acronym-itis, but my train of thought was broken. I wasted one Google search to find out that ESB meant “Enterprise Service Bus,” got fed up, and went to Starbucks. Of all the overused terms in software, “Enterprise” is by far the most annoying—although “Service” seems to be moving up in the world.

I’ve been developing loosely-coupled systems for awhile now, using all kinds of technologies, and never thought that I was doing anything particularly ground-breaking. So when the CIO came down and introduced me to the army of high-priced consultants that were going to help us redesign our software to become more “service-oriented” I really was interested in seeing what would be different. Soon after, I realized that the vendor-driven SOA meant nothing more than Web Services, XML, and loose coupling—with the mindset of loose coupling being the most important. I’d been “service-oriented” all this time and didn’t even know it. Oh, and it turns out that we didn’t have to redesign anything.

Imagine my utter joy in hearing that the reason our project was in trouble was that we didn’t have an ESB. And all this time I thought it was because the requirements were changing every two weeks.

It was about a month after that that our project manager got promoted for doing such a great SOA implementation and was now in charge of making the whole company, oops, sorry—enterprise, service oriented. I was made “acting project manager” and managed to do one really smart thing pretty quick—get our software through testing and deployed within the month, before too many new requests came in (I think it was possible because most of the stakeholders were on holiday). The system wasn’t that complex; we had the standard HR, accounting, inventory, etc., functionality split up into the same high-level components. Each top-level component had its own server-cluster and database. We pulled the data from each of the database to the data warehouse using classic ETL. Data flowed between the components primarily using publish-subscribe semantics while the client-side software just request-responded what it needed from each component.

We kept on working, pushing out features as fast as we could, until one morning I found the sysadmin at my door.

“We had a problem with some of the disks on the accounting cluster, so we installed it on a different cluster and brought the first one down. We tried a simple test to make sure everything was OK, and it wasn’t. A bunch of things don’t seem to be working.”

After looking around for a bit I found out that the sysadmins had forgotten to update the config files on the servers and the clients. We restarted the server components and they worked fine, but we couldn’t really go around restarting and changing config files on all the clients. Luckily, the sysadmins had it set up so that every client on our domain that logged in to the network could be sent a script to run, so pushing out the new config files was easy. As for the restarting part, we called up the help desk and told them that if (when) someone called about why their software wasn’t working properly, just to tell them to close it and run it again—which apparently is their standard first suggestion anyway.

Well, things lurched along like that for a while as we put out more and more functionality—put up a Web front-end, tied in some business partners, etc. I thought I had everything under control until our COO charged in, with the CIO in tow.

“Our business partners haven’t been able to send us orders for almost a week,” he fumed. “What did you do?!”

When money talks, you’d better believe everybody listens. After some seriously hectic hours of peering through diffs between the deployed source and the previously deployed source, we were getting nowhere. Somebody, I don’t remember who, had the common sense to get the sysadmins in there too. It turned out to have been the same problem as before, but this time with the inventory cluster. So we used the same solution. The problem was that our business partners’ software didn’t get the updated config files. While I was pondering how we could get the same system to work with external partners, my boss called me in for an urgent meeting.

“I just got a call from Jim (the CIO) and he wants you and me to help him explain what happened to the CEO.”

I started to get that sinking feeling, the kind where you know things are going from bad to worse. That afternoon, we all filed in to the chief’s office, bracing ourselves for the worst. He got directly to the point.

“If anything like this happens again, you three are fired. Now get the hell out of my office.”

How’s that for motivation?

And to top it all off, before he hurried off to another meeting, Jim asks us “You guys know about our first audit for Sarbanes-Oxley in three months, right? I don’t want to see any more screw-ups, and this SOX stuff is getting people anxious. We need full audit trails on everything.”

It looks like Moore’s law will continue indefinitely: You will need to handle twice as much crap today as you did 18 months ago.

It was at about this point where I realized that I needed help. I called up one of my old partners in crime, Clem, who had been doing large-scale distributed systems development for awhile. I told him my sorry tale and asked if he could give me a hand. Unfortunately, he was in the middle of some serious crunch time, but he left me with these pearls of wisdom:

“Udi, it’s all in the message. Forget about remote method invocations and pub-subbing events—down on the wire it’s all just messages. The trick is to think of your system as passing messages at the application level as well.

Asynchronous message passing over queues. It’s really quite simple.

Once you’ve packaged everything into the message, that message can be dynamically routed anywhere, and so can its responses. The application doesn’t need to bind against any specific endpoint—it just drops a message addressed to some logical location. Infrastructure can make sure that messages get to the logical recipient, even if they change physical locations.

That infrastructure is what brings about the “Bus” architectural style between your distributed components.”

Luckily I was writing down what he said, because I had to re-read it at least a dozen times for it to sink in. Flashback to that original conversation with the CIO—so that’s what ESBs are for! Well, you wouldn’t have guessed it with all the hype going on—IT/Business Alignment, like that’s going to happen any time soon.

After talking with some ESB vendors, I understood some nuances in what Clem told me. The message passing at the application level is really passing logical messages—a message is an object just like any other. The transformation that logical message undergoes in order to be sent across the wire is something else entirely. We can transform our message to and from XML, binary, text based key-value pairs—anything we need. Finally, the transport used to pass that wire-representation between machines is an infrastructure detail that is also independent of the logical message.

Once my mind wrapped itself around asynchronous messaging, the whole SOA thing became clear. The top-level components we were developing were providing top-level services—requests would queue up like people would at the teller in a bank. A component could send out the exact same message either as a broadcast or a unicast, where the recipients would be able to use the same semantics either way. Exposing a method, subscribing to an event, and handling a message were all the same, both internally and externally.

I can’t explain how much this simplified my view of the distributed world. It kind of felt like dominos—as one thing fell into place, it knocked down something else. I was finally beginning to understand what needed to be changed in our system—and all it took was a multi-million dollar mistake and nearly getting fired.

Needless to say, the whole SOX thing caused all hell to break loose. Our team wasn’t compliant, but then neither was any other team. The same goes for most of the company’s software. But, the reassuring thing for me, was knowing where I was going with our system. It took some time—we redesigned most of the communication paths, found a vendor whose product met our needs (at the right price), and several months later, we rolled out the new version. I wouldn’t say that the rollout was flawless, but I will tell you this—when the sysadmins moved a service from one cluster to another, no config files needed to be pushed out in order for things to work, and, more importantly, no orders were lost. I even got promoted from “Acting Project Manager” to “Project Manager” 🙂

Basic Messaging Infrastructure

Sunday, April 22nd, 2007

Download here.

Check out the ongoing discussion around the bus as well.

This implementation makes use of MSMQ so make sure you read the “readme.txt” for information on how to install it and what queues you need to define.

In order to have the “client” process send the “server” process a message, just press ‘Enter’ in its console.

Try to ignore the use of callbacks and subscriptions at first so you can hone in on the basic messaging semantics.

Questions and comments are more than welcome. Please send them to:


Service-Layer Separation of Concerns

Sunday, April 1st, 2007

The idea of having a generic bus object that dispatches message objects to their appropriate message handler objects seems to have struck a chord with Ayende (aka Oren). It is definitely one way of doing the Unit-of-Work Pattern that also partly goes along with the idea of Consumer-Driven Contracts, in that the consumer “defines” the transaction boundary. These two topics are directions that the Bus API was not originally intended to cover, but I’ve found them useful in many cases.

One of the strengths of this approach that isn’t immediately apparent is that you can have multiple classes that handle the same message type. These classes are then configured in the Bus to run in a certain order – very similar to the channel model in WCF, or the HTTP Handlers in ASP.NET. Each message handler in the chain can stop processing of the message if it should so choose.

The use of this strength is that it allows for a strong separation of concerns in the message handling logic. Need to do some pessimistic lock checking first? No problem – have a separate message handler class that does that. Want to add some custom auditing before and after all other processing, configure in a couple more message handlers. Have some complex validation logic that you’d like to keep separate from the rest of the business logic? Put it in its own message handler class.

For those thinking about more advanced messaging scenarios, you could have each message handler in the chain do some Content Enrichment and have that data available in down-stream handlers.

I’ll address the issue of sending messages using this pattern in a coming post, so stay tuned J

Autonomous Services and Enterprise Entity Aggregation

Tuesday, February 20th, 2007

Published in Issue 8 of the Microsoft Architecture Journal.

Summary: Enterprises today depend on heterogeneous systems and applications to function. Each of these systems manages its own data and often doesn’t explicitly expose it for external consumption. Many of these systems depend on the same basic concepts like customer and employee and, as a result, these entities have been defined in multiple places in slightly different ways. Entity aggregation embodies the business need to get a 360-degree view of those entities in one place. However, this business need is only one symptom of the larger issue: business/IT alignment. Service-oriented architectures (SOAs) have been hailed as the glue that would bring IT closer to business, yet the hype is already fading. We’ll take a look at concrete ways that autonomous services can be used to transform the way we develop systems to more closely match business processes and solve immediate entity aggregation needs.

Continue reading.


Don't miss my best content


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.”

Consult with Udi

Guest Authored Books

Creative Commons License  © Copyright 2005-2011, Udi Dahan. email@UdiDahan.com