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


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

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

For example

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

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

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

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

So what’s the problem

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

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

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

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

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

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

So is everything a long-running process then?

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

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

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

Deeper business analysis

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

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

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

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

In closing

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

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

Keep an eye out.

Comments [35]
Posted on Tuesday, August 31st, 2010.



NServiceBus – .NET Service Bus Smackdown


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

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

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

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

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

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

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

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

Comments [4]
Posted on Wednesday, August 4th, 2010.



Cautiously Merging IL


Caution, Merge AheadAs Dru mentioned on his blog, while having dinner in Kansas City, I described why NServiceBus makes use of IL Merge and some of the challenges we were facing with version management as a result. While I do think that we’ve managed to find the right balance, I must say that it wasn’t easy and I urge other developers use caution when employing it.

Mistakes Made

In the previous version of NServiceBus (1.9) we over aggresively merged 3rd party libraries like Castle into the NServiceBus binaries. That in itself, wasn’t the big problem. The problem was that we didn’t know about internalizing the libraries we merged.

This resulted in all the 3rd party types being exposed when a developer used NServiceBus. For those who happened to use the same version of those libraries as that which was merged, it wasn’t a problem. Unfortunately, developers who used libraries like Castle tended to be very particular about which version they used – which resulted in version conflicts, also known as “versioning hell”.

Internalization Challenges

As we moved to NServiceBus 2.0, we were a lot more careful about which libraries were merged and made sure to internalize them as much as possible. Yes, you read that right, “as much as possible”. You can’t always internalize all the types of a given library.

For example, NServiceBus internally uses NHibernate to persist the state of long-running processes (called sagas) and we want this implementation detail to not conflict with anything that developers want to do on top of NServiceBus. The only thing is that for NHibernate to work, it needs certain types to be exposed to the configuration environment, specifically all the types in the NHibernate.Cfg.MappingSchema namespace.

Extensibility Challenges

Once you take on an external dependency, you want to configure it to “just work” so that developers that aren’t familiar with it don’t have to learn yet another library to use your framework. So far, we’ve been able to do that quite successfully with NServiceBus. The challenge comes when developers want to customize the behavior of those 3rd party libraries, wanting to call into their APIs.

You see, once you internalize those libraries and their types, developers can’t access them. This leads to all sorts of tricky extensibility problems especially for different kinds of developers. Some are happy enough to configure things from the outside using XML – like using hbm.xml files to describe how their sagas get persisted, while others really want to use Fluent NHibernate, which is fully internalized.

Finding a Balance

What we’ve currently got for NServiceBus to try to keep everyone happy is a progressive exposure model. From the developer who’s downloading NServiceBus for the first time and wants everything to just work without changing anything, our API unfolds in multiple dimensions to allow for the highest level of extensibility and pluggability. That being said, the Fluent NHibernate issue mentioned above isn’t solvable at just an API level.

In order to address the class of developer that wants full control, we’ve got a “core only” build that doesn’t merge any assemblies into it. This class of developer usually doesn’t have a problem with referencing some more assemblies as long as they retain full control of the behaviors they want.

It ain’t easy keeping everybody happy, or, at least, not unhappy.

In Closing

I would agree that more OSS frameworks should merge and internalize 3rd party libraries that don’t need to be exposed to developers – it shortens the learning curve and increases adoption. But walk this path cautiously, it’s hard striking a balance that will work all users of your framework and it takes quite some time to get it right.

And one last thing, please, PLEASE, take care of maintaining binary compatibility from one version to the next. I know it’s a pain – we’ve been doing it with NServiceBus for the past 3 years, but your users will thank you for it.

Comments [5]
Posted on Sunday, August 1st, 2010.



Course Update


Posted in Courses

Just wanted to let you know that there is a scheduling change for my upcoming courses. This is due to some minor issues internal to Skills Matter, the company that hosts my training in the UK and manages the France location as well. Anyway, these issues have been resolved but the scheduling changes remain.

The courses that were planned to be delivered in Paris, France and London, UK have been merged and will now be delivered in the UK on the week of Sep 13 – the original dates of the France course. Just to make it clear, the course planned for Aug 2 in the UK will *not* be taking place. You can register for the UK course here.

All the other locations will not be affected, and are as follows:

Toronto, Canada – Aug 8
Calgary, Canada – Sep 27
Johannesburg, South Africa – Oct 11
Sydney, Australia – Nov 22

I’m still in the process of getting a venue for the Seattle WA, USA course on Dec 13.

I also wanted to say that I’ll be cutting down on the number of deliveries of this course next year, most likely limiting the number of locations to 2 or 3, so if you’ve been waiting for me to come to your home town, well, I’m sorry to dissappoint you, but that probably won’t happen. So, if you do want to take the course, I suggest you register for the closest location to you above.

Looking forward to seeing you there.

Comments
Posted on Saturday, July 24th, 2010.



Evolving Loosely-Coupled Frameworks & Apps


This post will be less of a big-concept type posts I usually do, and more of a tip for people building and maintaining infrastructure and frameworks either open-source or internally for their companies. I’m going to illustrate this with NServiceBus as it is a large enough code base to have significant complexity and open so that you can go and take a look yourself. Trying to include some example in here would be just too small to be useful or for the point to come across.

Some background

As a cohesive framework, NServiceBus makes it quite easy for developers to pick and choose which settings they want turned on and off. Being built as a loosely-coupled set of components that don’t know about each other has always kept the internal complexity low. But as the NServiceBus API has been evolving over the years, and the functionality offered has increased, some interesting challenges have popped up as the codebase has been refactored.

The challenge

The UnicastBus class has grown too large and it’s time to refactor something out. Coincidentally, users have been asking for a better “header” story for messages – the ability to specify static headers that will be appended to all messages being sent (useful for things like security tokens), as well as per message headers. So, we want to refactor all the header management out to its own component independent of the UnicastBus class.

So, here’s the issue. So far, users have specified “.UnicastBus()” as a part of the fluent code-configuration, and shouldn’t have to change that – they shouldn’t need to know that header management is now a separate component. But then how can the new component bootstrap itself into the startup, such that it gets all the dependency injection facilities of the rest of the framework? Remember that the component doesn’t know which container technology is being used (since the user can swap it out) or when the container has been set.

The solution

The only part of the framework that knows about when all DI configuration is set is the configuration component, thus it will have to be the one that invokes the new component (without knowing about it). Introduce an interface (say INeedInitialization) and scan all the types loaded looking for classes which implement that type, register them into the container, and invoke them. Have the new component implement that interface, and in its initialization have it hook into the events and/or pipelines of other parts of the system.

Other uses

One historically problematic area in NServiceBus has been people forgetting to call “.LoadMessageHandlers()”. This can now be wired in automatically by a class in the UnicastBus component via the same mechanism.

A new feature coming in the next version is the “data bus”, a component which will allow sending large quantities of data through the bus without going through the messaging pipelines. This will help people get around the 4MB limit of MSMQ and, even more importantly, the much smaller 8KB limit of Azure. We will be able to introduce the functionality transparently with the same mechanism.

As an extension point, developers can now enrich the NServiceBus framework with their own capabilities and make those available via the contrib project to the community at large. This is better than the IWantToRunAtStartup interface that was only available for those using the generic host (which excluded web apps) and gives a consistent extensibility story for all uses.

Summary

Extensibility has always been a challenge when writing object-oriented code and dependency injection techniques have helped, but sometimes you need a bit more to take things to the next level while maintaining a backwards-compatible API.

Like I said, not a ground-shaking topic but something quite necessary in creating loosely-coupled frameworks and applications. Once you know it’s there, it isn’t really a big deal. If you didn’t know to do it, you may have been contorting your codebase in all kinds of ways to try to achieve similar things.

If you want to take a look at the code, you can find the SVN repository here: https://nservicebus.svn.sourceforge.net/svnroot/nservicebus/trunk/

Comments [1]
Posted on Wednesday, July 14th, 2010.



High Availability Presentation


OK – this is the last one, I promise. Well, for now, anyway.

Earlier this month at TechEd North America I gave a fairly new presentation that was only delivered once before (at the Connected Systems User Group in London) and I’m happy to say is now online for your viewing pleasure.

High Availability – A Contrarian View

Comments? Thoughts? Let me know.

Comments [4]
Posted on Monday, June 21st, 2010.



CQRS, DDD, and NServiceBus video


Following the theme of my last few blog posts, this post will also be pointing you to videos of me talking.

After I had finished speaking at QCon London last March, I sat down for a short interview with the guys from InfoQ chatting about topics from CQRS, to DDD, to NServiceBus. I’m happy to say that the interview is now online with a full (and mostly accurate) transcript as well as with an MP3 download link.

Get it here: Udi Dahan on CQRS, DDD and NServiceBus

Comments
Posted on Friday, June 18th, 2010.



DDD Exchange London 2010


Posted in DDD | Presentations

Last Friday I was in London for the DDD Exchange. It was great seeing Eric Evans again and Greg Young, who I haven’t seen for at least a couple of years. It might take some time for Skills Matter to get the videos online so in the mean time I wanted to point you to Gojko blog post where he pretty much transcribed my talk word for word.

Update

The recording of the talk is now online and can be found here.

You can find the slides for my talk here.

Comments [2]
Posted on Thursday, June 17th, 2010.



NServiceBus Presentation Now Online


Last April I was in Bergen Norway for some consulting and training and I also gave my first NServiceBus presentation to a user group. I don’t particularly like giving NServiceBus-specific presentations, preferring to talk about the patterns and concepts of service-based architectures and service buses – NServiceBus is just an implementation. Ultimately, that’s what happened in the presentation – in the first half (or so) I talked about the theory, and in the second I demonstrated that theory with NServiceBus.

Currently, the video is being graciously hosted by Jon Torresdal on his blog, so let’s hope that the bandwidth holds up.

Get it here.

Comments [3]
Posted on Wednesday, June 9th, 2010.



Server Naming and Configuration Conflicts


ConfigurationIn my work with clients the topic of how to handle the movement of software from one environment to another inevitably comes up. Sometimes this is in the context of NServiceBus but the problem is more generic. The faster that an organization is able to get software out the door, the more agile they can be.

Unfortunately, there is one tiny little mistake that I see almost everywhere that gets in the way, and that’s going to be the topic of this post.

The Problem

Let’s say you have a standard web app environment – some web servers, application servers, and a database server. Your web servers need to send messages to the application servers. So far, so good.

In your test environment, you have an application server called AS_01_Test, and your web servers are configured to send it messages. However, in your staging environment the application server fulfilling that same role is called AS_01_Stage. This creates a configuration problem – you need to change the config of your web servers as you move the web app from Test to Staging.

I’ve seen companies doing all sorts of creative things to get around this problem – some of them involve putting all configuration settings in a database so that they can be centrally managed and visualized. I’d like to suggest an alternative approach.

What if…

What if server names were the same across all environments?

Well, you wouldn’t need to change configuration as you moved the system between environments. That’s a good thing.

But how can that be? Wouldn’t there be a conflict if there were two machines with the same name?

The answer is that there wouldn’t be a conflict if the machines were on different networks. Not all machines have to be on the same network. We can set up as many networks / virtual networks as we like. And it is clear that we don’t need machines in one environment / network to talk to machines in another environment. I mean, under no circumstances would we want web servers in our test environment to talk to application servers in the production environment.

These separate networks provide much needed isolation, beyond solving the server naming problem.

In closing

It’s really a tiny thing when you think about – multiple networks. But that’s exactly why software developers overlook it so often – because it’s not a “software solution” to the configuration problem we perceive as a “software problem”.

I wrote about related multi-environment configuration issues in this earlier post: Convention over Configuration – The Next Generation

I’m happy to say that this functionality is now in NServiceBus called “profiles” and you can read more about how they work here.

How are you handling the flow of moving software through to production? Leave your comments below.

Comments [9]
Posted on Saturday, June 5th, 2010.



   


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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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