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Archive for the ‘Reliability’ Category



UI Composition vs. Server-side Orchestration

Monday, July 9th, 2012

orchestra_compositionFollowing on my last post called UI composition techniques for correct service boundaries, one commentor didn’t seem to like the approach I described saying:

“I’m sorry, but with all due respect I must strongly disagree. You haven’t avoided any orchestration work at all, you’ve just moved it in to client side script!

How are you going to deal with the scenario that one of the service calls fails? Say a failed credit card payment, or no more rooms left? In more javascript??

I would much rather take the less brittle approach of introducing an orchestration service. Like it or not, however trivial it may be, there is a relationship between these services, if one call fails, they both fail. This should be reflected in the architecture, not hidden in javascript. With an orchestration service you also either get transactions for free provided by infrastructure, or alternatively if the underlying service doesnt support this, explicit and unit testable control over recovery.”

Since this is a common point of view, I thought I’d take the time to explain a bit more.

Let’s start at a fairly high level.

On failures

I’ve talked many times in the past about how to handle technical causes for failure like server crashes, database deadlocks, and even deserialization exceptions. Messaging and queuing solutions like NServiceBus can help overcome these issues such that things don’t actually fail – they just take a little longer to succeed.

On the logical side of things, the CQRS patterns I talk about describe an approach where aggressive client-side validation is done to prevent almost all logical causes for failure. The only thing that can’t be mitigated client-side are race conditions resulting in actions taken by other users at the same time.

In short, it really is uncommon for things to fail when being processed server-side.

Back to the specific example

The concerns raised in the comment specifically talked about a failed credit card payment or no rooms left in the hotel, so let’s start with the credit card thing:

In my last post I talked about collecting guest and credit card information from the user as a part of the “checkout” process when making a reservation for a hotel room. Just to be clear – there is a final “confirm your reservation” step that happens after all information has been collected.

What this means is that we aren’t actually charging the customer’s card when we collect that data, therefore there is no real issue with a failed credit card payment that needs to be handled by the client-side javascript. When the customer confirms their reservation, yes, there might be a failure when charging the card though there are only some specific types of rates for which the hotel charges your card when you make a reservation.

In general, failed credit card payments are handled pretty much the same way for all ecommerce – an email is sent to the customer asking for an alternative form of payment, also saying that their purchase won’t be processed until payment is made.

In any case, it is only after the reservation is placed that the responsible service would publish an event about that. The service which collected the credit card information would be subscribed to that event and initiate the charge of the card when that event arrives (or not, depending on the rate rules mentioned).

With regards to there not being any rooms left, well, first of all, there’s overbooking – hotels accept more reservations than rooms available because they know that customers sometimes need to cancel, and some just don’t show up. Secondly, there is a manual compensation process if more people show up than there are actual rooms to put them in. In some cases, a hotel will bump you up to a higher class of room (assuming there aren’t too many reservations for those), and in others they will call a “partner” hotel nearby and put you up there instead.

In summary

While arguments can be made that yes, these issues have been addressed in this specific example, there may be other domains where it is not possible to do these kinds of “tricks”. Although I do agree with that in theory, I’ve spent the better part of 5 years travelling around the world talking to hundreds of people in quite a few business domains, and every single time I’ve found it possible to apply these principles.

In short, the use of UI composition allows services to collect their own data, making it so anything outside that service doesn’t depend on those data structures which makes both development and versioning much easier. Technical failure conditions can be mitigated at infrastructure levels in most cases and other business logic concerns can be addressed asynchronously with respect to the data collection.

Give it a try.



Logically Distributed, Physically Centralized

Sunday, May 6th, 2012

centralized-distributedWhen people pull back the covers on something like MSMQ, particularly its private queues (the way NServiceBus uses it), and they see that MSMQ is storing its messages in C:WindowsSystem32, well, they’re not particularly happy.

One of the reasons they worry about these types of distributed or federated queue-based solutions has to do with physical failures. The concern is that messages would be lost if there was a hard drive failure.

The preference for centralized message broker type solutions is that we can set it up on a nice RAID infrastructure that will take care of any physical reliability concerns. (Just so that we’re clear here – I’m talking about an single datacenter, possibly connected to a disaster recovery site.)

So, here’s the thing:

Virtualization

You see, in a virtualized production environment, the C drive of a virtual machine is physically in the image file of that VM, which is sitting on a SAN (storage area network).

What that means is that when a message is sent from one processing node to another, the data of that message ends up being written to the SAN, with all of its redundant disks. Even if one of the machines has a critical failure and cannot start up again, all the VMs that were running on it can be started up on a different machine without any message loss.

In fact, most virtualized environments have monitoring and management capabilities built-in so that the VMs will be brought up automatically on another machine. Even if you aren’t using messaging, there are so many other benefits that virtualization brings that you probably should be planning on putting it in, if you haven’t already.

Databases too

In fact, many people do the same thing with databases.
The file partitions on which the database server actually stores its data are on the SAN.

Think about that for a second.

All the data in messages flowing through your queues, and the data in the database, on a SAN. This gives you the ability to do a fully consistent backup of the entire system with SAN snapshots, not to mention ship those to your disaster recovery site.

In closing

Distributed solutions are often misunderstood.
Bad experiences in the past with MSMQ can color perceptions in the present.

The thing is that today’s infrastructure is set up to handle distributed solutions much better.
Developers no longer have to turn to centralized broker or database technologies to get the centralized backup and restore capabilities administrators look for.

If you’ve been avoiding NServiceBus for these reasons, give it a try. Not only will it make your life as a developer easier, combined with this virtualization thing, it will make your administrators life easier too.



NServiceBus in Insurance – Testimonial

Friday, March 30th, 2012

Getting more companies willing to go on the record about their usage of NServiceBus.

Update: Check out full list of customers.

Here’s a testimonial from a large insurance company whose name always had me wondering…

if_logoIf P & C Insurance is the leading property and casualty insurance company in the Nordic countries with 3.6 million customers and 6400 employees. NServiceBus was chosen as the ESB for one of our core insurance systems and is currently processing around 100,000 insurance policies a month. We expect that number to double within a year.

The support NServiceBus provides around asynchronous messaging and publish/subscribe communication makes the implementation of Service Oriented Architectures very straightforward. While the performance and scalability of the platform is able to handle the massive loads we’re under, we’re just as pleased with how quickly developers are able to get started with NServiceBus – even those coming into the project later on benefit from the maintainability of NServiceBus-centric code. We already have over 30 developers using it.

Looking forwards, we will be using NServiceBus on more systems at ever larger scales.



Video Online: Who Needs a Service Bus Anyway?

Saturday, March 17th, 2012

My presentation at Oredev on “Who needs a service bus anyway?” is now online for your viewing pleasure. Enjoy.



The Myth Of “Infinite Scalability”

Thursday, December 29th, 2011

globeScalability is a topic near and dear to my heart.

Many a client seeks me out for the first time for help in this area.

Usually the request is for an amount substantially smaller than infinity.

It’s usually on the discussion groups and in conference presentations that infinity is brought into it.

The basics

The first issue with scalability is the use of the word as an adjective: scalable.

“Is the system scalable?”

Or the similar verb use: “Does it scale?”

The problem here is the implication that there is a yes/no answer to the question.

Scalability is not boolean.

Linear Scalability

scalabilityWhen people talk about scalability, or a system being able to scale, they’re usually referring to a graph that looks something like this:

The red graph indicating a system that does not scale well, the green graph indicating one that does.

What is missing from this diagram are the labels of the axes.

The Y axis is Cost, Expense, or Money.
The X axis is usually the number of users (for internet-type companies).

Ultimately, scalability is a cost-function that will tell us how much it will cost to have the system support a certain number of users.

Linear scalability is when the cost of the next user is the same as the cost of the previous user. This means our system doesn’t have bottlenecks. This is what people usually mean when they say “infinite scalability”.

But there’s more

As many of the internet companies (and their investors) have realized over the years, there’s a difference between the number of users and the number of active users. It’s very easy to scale to a billion users when only 1000 of them are active at any given time.

To be more accurate, what we want is additional X-axes for things like total data managed by the system, number of requests per user, resource utilization per request, propagation speed (how quickly information entered by one user needs to be visible to others), and more.

Scalability is a multi-dimensional cost function, where part of an architects job is to figure out which dimensions are significant for the system/business, and what the expectation for growth is across each axis.

Preparing for “infinity”

Be careful not to optimize for only a single dimension – reality is a whole lot more complex.

There are so many other things to deal with as a system scales.

For example, do you really think you’re going to want your configuration entirely centralized? Putting everything in one place means easier management, yes, but it also means a mistake will instantly affect everyone. Is it worth the risk? Maybe instead of centralization, we could do with some automation that will allow a staged rollout of configuration changes with the ability to rollback.

The same goes for rolling out new versions, patches, and upgrades.

But that now means we may have multiple versions of the same system in production at the same time. How will that work? Will they all talk to the same database? How will we version the database then? If not, how will we handle state? Won’t this mean our code will have to be backwards compatible from one version to another? Isn’t that hard? Like, insanely hard?

Please, can we park the whole “infinite scalability” thing?
It’s really not the most important concern – not by a long shot.



Inconsistent data, poor performance, or SOA – pick one

Sunday, September 18th, 2011

One of the things that surprises some developers that I talk to is that you don’t always get consistency even with end-to-end synchronous communication and a single database. This goes beyond things like isolation levels that some developers are aware of and is particularly significant in multi-user collaborative domains.

The problem

Let’s start with an image to describe the scenario:

Inconsistency

Image 1. 3 transactions working in parallel on 3 entities

The main issue we have here is that the values transaction 2 gets for A and B are those from T0 – before either transaction 1 or 3 completed. The reason this is an issue is that these old values (usually together with some message data) are used to calculate what the new state of C should be.

Traditional optimistic concurrency techniques won’t detect any problem if we don’t touch A or B in transaction 2.

In short, systems today are causing inconsistency.

Some solutions

1. Don’t have transactions which operate on multiple entities (which probably isn’t possible for some of your most important business logic).

2. Turn on multi-version concurrency control – this is called snapshot isolation in MS Sql Server.

Yes, you need to turn it on. It’s off by default.

The good news is that this will stop the writing of inconsistent data to your database.
The bad news is that it will probably cause your system many more exceptions when going to persist.

For those of you who are using transaction messaging with automatic retrying, this will end up as “just” a performance problem (unless you follow the recommendations below). For those of you who are using regular web/wcf services (over tcp/http), you’re “cross cutting” exception management will likely end up discarding all the data submitted in those requests (but since that’s what you’re doing when you run into deadlocks this shouldn’t be news to you).

The solution to the performance issues

Eventual consistency.

Funny isn’t it – all those people who were afraid of eventual consistency got inconsistency instead.

Also, it’s not enough to just have eventual consistency (like between the command and query sides of CQRS). You need to drastically decrease the size of your entities. And the best way of doing that is to partition those entities across multiple business services (also known in DDD lingo as Bounded Contexts) each with its own database.

This is yet another reason why I say that CQRS shouldn’t be the top level architectural breakdown. Very useful within a given business service, yes – though sometimes as small as just some sagas.

Next steps

It may seem unusual that the title of this post implies that SOA is the solution, yet the content clearly states that traditional HTTP-based web services are a problem. Even REST wouldn’t change matters as it doesn’t influence how transactions are managed against a database.

The SOA solution I’m talking about here is the one I’ve spent the last several years blogging about. It’s a different style of SOA which has services stretch up to contain parts of the UI as well as down to contain parts of the database, resulting in a composite UI and multiple databases. This is a drastically different approach than much of the literature on the topic – especially Thomas Erl’s books.

Unfortunately there isn’t a book out there with all of this in it (that I’ve found), and I’m afraid that with my schedule (and family) writing a book is pretty much out of the question. Let’s face it – I’m barely finding time to blog.

The one thing I’m trying to do more of is provide training on these topics. I’ve just finished a course in London, doing another this week in Aarhus Denmark, and another next month in San Francisco (which is now sold out). The next openings this year will be in Stockholm, London; Sydney Australia and Austin Texas will be coming in January of next year. I’ll be coming over to the US more next year so if you missed San Francisco, keep an eye out.

I wish there was more I could do, but I’m only one guy.

Hmm, maybe it’s time to change that.



NServiceBus 2.5 Released

Friday, December 31st, 2010

Just before we usher in the new year, I’m happy to announce the release of NServiceBus version 2.5.

Go to the NServiceBus website

Yes, there’s a new logo, and the website’s been redesigned.
It’s been a long time coming – the previous version (2.0) was released in March.

I’m really quite excited about this version as it rolls up all the bug fixes and enhancements that customers have asked for as they ran version 2.0 under the most severe types of production environments. The next thing that is a big deal that many have been asking for is a licensed version of NServiceBus – that is, the ability to purchase a commercial license and receive support.

We all know how managers like having a throat to choke.

And now they’ll have one – NServiceBus Ltd is the company that will be providing licensing, services, and support for all customers’ NServiceBus needs. After more than 33,000 downloads and over 1000 developers in the community, the demand has really grown. Who would’ve thought all this would happen when I started NServiceBus 4 years ago (before it even had a name).

Why NServiceBus is better than WCF for your distributed systems

This question comes up repeatedly for people hearing about NServiceBus for the first time.

The answer is simple – reliability.

A system built with NServiceBus is so much more reliable to all kinds of production conditions than WCF that it’s hardly a fair comparison at all. While WCF can be configured to provide something kind of close to the same level of reliability, you need to do a fair amount of spelunking through the various options of netMsmqBinding to get it right.

The second reason to use NServiceBus instead of WCF is publish/subscribe.

The ability to make use of events and the observer pattern not just to achieve loose coupling within a single process, but across many processes, machines, and sites. Can you imagine going back to programming without events? Shudder. But that’s exactly what it’s like to use WCF in your distributed system. NServiceBus brings you the best of object-oriented programming but in a distributed and reliable infrastructure.

Don’t wait any longer

Take NServiceBus for a spin.

But things may look a bit different after you do…

RedPillBluePill

http://www.NServiceBus.com

And have a happy New Year.



High Availability Presentation

Monday, June 21st, 2010

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.



Lost Notifications? No Problem.

Sunday, December 7th, 2008

One of the most common questions I get on the topic of pub/sub messaging is what happens if a notification is lost. Interestingly enough, there are some who almost entirely write-off this pattern because of this issue, preferring the control of request/response-exception. So, what should be done about lost messages? The short answer is durable messaging. The long answer is design.

Durable Messaging

In order to prevent a message from being lost when it is sent from a publisher to a subscriber, the message is written to disk on the publisher side, and then forwarded to the subscriber, where it is also written to disk. This store-and-forward mechanism enables our systems to gracefully recover from either side being temporarily unavailable.

In my MSDN article on this topic, I outlined some problems with this approach. These problems are exacerbated for publishers. Imagine a publisher with 40 subscribers, publishing 10 messages a second, each containing 1MB of XML. If 10 of the subscribers are unavailable, that’s 100MB of data being written to the publisher’s disk every second, 6GB every minute. That’s liable to bring down a publisher before an administrator brews a cup of coffee.

Publishers have no choice but to throw away messages after a certain period of time.

Publisher Contracts

The whole issue of contracts and schema is considered one of the better understand parts of SOA. Unfortunately, the operational aspects of service contracts is hardly ever taken into account.

On top of the schema of the messages a service publishers, additional information is needed in the contract:

  1. How big will this message be?
  2. How often will it be published?
  3. How long will this message be stored if a subscriber is unavailable?

This first two pieces of information are important for subscribers to do load and capacity planning. The last one is the most important as it dictates the required availability and fault-tolerance characteristic of subscribers.

For Example

In the canonical retail scenario, when our sales service accepts an order, it publishes an order accepted event. Other services subscribed to this event include shipping, billing, and business intelligence.

While shipping and billing are highly available and able to keep up with the rate at which orders are accepted, the business intelligence service is not. BI has two main parts to it – a nightly batch that does the number crunching, and a UI for reporting off of the results of that number crunching. Some even do the reporting in a semi-offline fashion, emailing reports back to the user when they’re ready.

Furthermore, nobody’s going to invest in servers for making BI highly available.

And wasn’t the whole point of this publish/subscribe messaging to keep our services autonomous? That not all services have to have the same level uptime?

Houston, do we have a problem.?

Data Freshness

There is a glimmer of light in all this doom and gloom.

Not all services have the same data freshness requirements.

The business intelligence service above doesn’t need to know about orders the second they’re accepted. A daily roll-up would be fine, and an hourly roll-up bring us that much closer to “real time business intelligence”.

So, while BI is ready to accept the sales message schema, it would like a slightly different contract around it – less messages per unit of time, more data in each message.

From the operational perspective of the sales service, it would be cost effective to have less “online” subscribers. It could even take things a few steps further. Instead of using the regular messaging backbone for transmitting these hourly messages, it could use FTP. The data could even be zipped to take up even less space. Since the total data size is less than the corresponding online stream, is stored on cheaper, large storage, and the number of subscribers for this zipped, hourly update is fairly small, these messages can be kept around far longer.

If you’ve heard about consumer-driven contracts, this is it.

Note that we’re still talking about the same logical message schema.

Summary

It’s not that lost notifications aren’t a problem.

It’s that they feed the design process in such a way that the resulting service ecosystem is set up in such a way that notifications won’t get lost. I know that that sounds kind of recursive, but that’s how it works. Either subscribers take care of their SLA allowing them to process the online stream of events, or they should subscribe to a different pipe (which will have different SLA requirements, but maybe they can deal with those).

It make sense to have multiple pipes for the same logical schema.

It’s practically a necessity to make pub/sub a feasible solution.

 


Related Content

MSDN article on messaging and lost messages

Durable messaging dilemmas

Additional logic required for service autonomy

More in depth example on events and pub/sub between services

Consumer-Driven Contracts



Reliability, Availability, and Scalability

Saturday, November 15th, 2008

The great people at IASA have made the recording for my webcast available online:

The slides can be found here.

I also gave this talk at TechEd Barcelona and wanted to thank the attendee who posted this comment:

“You’ve done it again. Everytime I attend a session of yours I leave the room with new insights and inspiration on how to improve my software…”

You made my day.



   


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

97 Things Every Software Architect Should Know



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