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Archive for the ‘WCF’ Category
Friday, April 11th, 2008
There’s a new article up on MSDN describing how to write Smart Clients using WCF. The author is none other than WCF-Master Lowy and he goes over the multitude of ways you can deadlock yourself.
Here’s a taste:
UI Thread and Concurrency Management
Whenever you use hosting on the UI thread, deadlocks are possible. For example, the following setup is guaranteed to result with a deadlock: A Windows Forms application is hosting a service with UseSynchronizationContext set to true, and UI thread affinity is established. The Windows Forms application then calls the service over one of its endpoints. The call to the service blocks the UI thread, while WCF posts a message to the UI thread to invoke the service. That message is never processed, because of the blocking UI thread—hence, the deadlock.
Another possible case for a deadlock occurs when a Windows Forms application is hosting a service with UseSynchronizationContext set to true and UI thread affinity is established. The service receives a call from a remote client. That call is marshaled to the UI thread and is eventually executed on that thread. If the service is allowed to call out to another service, that can result in a deadlock if the callout causality tries somehow to update the UI or call back to the service’s endpoint, because all of the service instances that are associated with any endpoint (regardless of the service-instancing mode) share the same UI thread.
Similarly, you risk a deadlock if the service is configured for reentrancy and it calls back to its client. You risk a deadlock if the callback causality tries to update the UI or enter the service, because that reentrance must be marshaled to the blocked UI thread.
Actually, I have difficulty believing that Juval would go so far as to suggest that even the forms should be services, but he does:
Form as a Service
The main motivation for hosting a WCF service on the UI thread is if the service must update the UI or the form. The problem is always: How does the service reach out and obtain a reference to the form? While the techniques and ideas that appear thus far in the listings certainly work, it would be simpler yet if the form were the service and hosted itself. For this to work, the form (or any window) must be a singleton service. The reason is that singleton is the only instancing mode that enables you to provide WCF with a live instance to host. In addition, you would not want a per-call form that exists only during a client call (which is usually very brief), nor would you want a per-session form that only a single client can establish a session with and update.
When a form is also a service, having that form as a singleton service is the best instancing mode all around.
I think that this article serves as a great treatise leading to only one conclusion – you’d have to be crazy to try to do this without some higher level framework, preferably with a different low-level framework too 🙂 . Sucks Microsoft didn’t put one out – nor is there a pending beta, CTP, or even word about some project with a codename handling this. From what I know about Prism, it doesn’t intend to handle this issue either.
One thing that isn’t covered in the article is that if you do choose not to tie the client-side service to the UI thread, you open yourself up to race conditions. Reasons you’d want to handle messages on a different thread center around UI responsiveness. I’ve written about these things before:
The more I read things like this, the more I feel that I have to get going with my nServiceBus based solution. I’m fairly swamped as it is, so if anyone is interested in helping get this project off the ground, I’d be most grateful – as I think anyone else that had to build a smart client would.
Posted in Architecture, Development, NServiceBus, Simplicity, Smart Client, Threading, WCF | 2 Comments »
Thursday, February 21st, 2008
Well, I had almost forgot about that interview.
When I was at TechEd Barcelona last November (07), the morning after I flew in I experienced “the fish bowl” and Virtual TechEd for the first time. Anyway, after a short chat – and quite to my surprise, my interviewer, Paul Foster, decided that we should talk about nServiceBus.
So here it is. The Microsoft/Marketing friendly description of what nServiceBus is and how nicely it plays with things like WCF and WF. Always be a gracious guest. Don’t bite the hand that feeds you. But a nibble here and there – well, that you can get away with 🙂
Download:
Virtual TechEd site is gone and in it’s place is something else, not related to software.
Posted in NServiceBus, Presentations, WCF, Workflow | No Comments »
Monday, January 14th, 2008
A while ago, me and Ron Jacobs (virtually) got together and did a couple “rapid responses” to questions on the MSDN architecture forums, and I just noticed that they’re online. The really great thing is that there are transcripts! For your convenience, I’ve included them here.
By the way, if you’re looking for more Q&A style info, check out the Ask Udi podcast. If you have a pressing question and need a shorter turn around time than the month or so it usually takes me for the podcast, send me an email to OnlineConsultation@UdiDahan.com.
Number 1
Ron: Hey, welcome back to ARCast Rapid Response. This is your host Ron Jacobs and today I’m looking at the MSDN architecture forum where I see this message from “theking2.” Yeah? OK, so “king,” he says, he’s building a distributed architecture that has a number of external systems. These external systems interface through a telnet connection and so they accept commands and return results as ACKS or NACKS.
Typically these systems have limited resources for the number of simultaneous sessions you can open, so, five to fifty depending on the system. What he did to get around this, was, he created some Enterprise Services objects and some pooled objects that set up these connections and then he has some Web services. The Web services are going to receive an incoming message. They’re going to call these pooled COM+ objects and they’re going to make the telnet calls to the external systems. Sounds interesting.
He says, after a year of production it has become apparent that some of the external systems are not performing very well. He says the bulk of the requests, but not all, to the external systems can be done asynchronously. So, he’s opting for a message queue-based solution using pseudosynchronous calls whenever a direct response is needed.
So, the question is, at what layer would message queuing make most sense?
So, should the clients, this Web service that receives the message — should it do a queue? Put a message in the queue and then the COM+ objects would pop off or they have some central Web services that would pop it. So, the central Web services or these Enterprise Service objects? Or maybe just a communication at the top of the telnet. He says this is the first time when he’s using message queuing.
On the line with me I have Udi Dahan, the Software Simplist from Israel.
Udi, this is a very interesting application and my first gut reaction is, does it really matter where you put the queuing?
Udi Dahan: Well, actually I took a look at it as well and I’d have to say that it does because the problem that he’s trying to solve isn’t that clear. We know that there is some sort of performance problem but we’re not quite sure where it is. We know that there are long and varying latencies in the responses but we’re not really quite sure why.
While we know that their external system is a bit slow but our choice of where to put the queue will probably have an impact, obviously on the development model of the clients and the Web services as well as how those external systems would work. So, I’d have to say that choosing the correct place to put the queue is important.
Ron: Well, let me interject something here because what you said just made me think. Now, if the problem is that these external systems are slow and limited number of connections, the first question we ought to ask is, does queuing help this situation at all?
Udi: Well, that’s probably a good first step. I mean every single time someone comes with a solution and then says, “OK, what’s the problem,” it’s always a good thing to check that solution first.
It looks like the problem that he has here has to deal with or the reason that he wants to use a queue is to do some kind of load leveling. He’s getting too many requests or at too high a rate from his clients and external Web services and external web applications more than his back end systems can use. So, using a queue as a load leveling mechanism is definitely the right way to go. So, from that perspective I think that putting a queue somewhere in there is a good idea.
Ron: OK. So then if you put a queue, it seems to me that it’s not going to make that much difference which layer you put the queue, would it?
Udi: Well, it might for the main reason that you really have to look at where his bottleneck is and that’s his back end systems. The bottleneck also has to do with the number of connections that can be opened and the number of sessions that can be opened. The place that I’d be looking at doing that is probably between those pooled COM+ objects and his central Web services for the main reason that that really gives a nice encapsulation in terms of the Web services towards both his organization’s internal services if they are other Web services, web applications or clients and everybody else that’s going on out there while keeping that abstraction out of the way.
So, the choice of using pooled COM objects is one of the ways he does the load leveling now. One of the problems he has is that it doesn’t seem to be doing that much for him because the switches and knobs that are available in COM+ in order to do that load leveling aren’t that great. What I’d be looking at in his situation is to put a queue in there but on the back side of that queue, not talking directly to the external system but doing something with WCF.
WCF has an incredible amount of switches and knobs in order to do the load throttling and the number of threads that are open. He could also do that on a large number of URIs in order to sort of split up the load from that perspective allowing him to cache results quite a bit better. So, that’s where I’d be looking at too. Just throw away those COM+ objects, put WCF in there, use the MSMQ binding and start configuring things from there.
Ron: There’s a lot of stuff in the message, but I think his core concern is performance. He mentions pseudosynchronous calls. I think by that he means, a message comes in to the web service, he’s going to drop something on the queue and then hold that message response until he gets a response back from a queue. So, it’s sort of synchronous but sort of not synchronous. So, in effect he’s kind of waiting on a queue instead of waiting on the pooled object to make this outbound telnet call.
I could agree if you said, “Well, look, our big problem is that we keep getting time outs because when we go to get a COM+ object from the pool, COM+ waits for a while and then it says, “Hey, there’s no object available’ and it returns an error,” then the queue is definitely going to help that problem. But in terms of the sheer through put or performance of the system, this is not going to help at all. It’s going to still be the same performance.
Now if you said, “Oh look, we can do some of this work kind of at a later point in time, ” well queuing doesn’t allow you to time shift the work. Right? So, if you said, “Look we can rethink this solution.” So you get a message in, we stuff something in a queue that we’ll deal with later, and then very quickly return a response like some kind of a number like, hey “your transaction number blah, blah, blah, will be processed later, it’s queued for processing, ” whatever.
I mean that introduces a lot of complexity in the system but it clearly would provide better response at the Web service layer. What do you think?
Udi: Well I think that at the most basic level, his throughput is dictated by his back end systems. From what he seems to be describing, every single request that is going through there, has to hit that back end system. If he has a limited number of back end systems that are supporting a limited number of connections, that’s going to limit his throughput no matter what technology he puts in front of that. So that’s at the core level. You just can’t get away from that.
The one thing that I would agree with you in your description there is the choice of using those COM+ objects. I mean COM+ was a great technology when it came out. The problem occurs, of course, when we start getting into larger and larger delays around the response time and we start getting all sorts of time out exceptions and things like that. So in that respect, I definitely say you know, take a step back from there.
But in terms of everything that he has around there, the queue isn’t going to make the back end system run any faster. What it will do is definitely complicate his system because he’s taking something that used to be synchronous and making it asynchronous. Writing Web services in order to handle that, I mean just adding a bunch of threads in order to listen to queues is not going to make things any simpler.
However, what it might do is to improve the resource usage of those Web services, OK? So instead of having those Web services have a bunch of threads open, waiting for the response coming back from those COM+ pooled objects, those threads could be relinquished and really just be triggered back up when a response comes back from the queue.
So I don’t see an improvement in the kind of solution that MSMQ or queuing would put in there in terms of the latency — how long it would take for a response to get back. However, I do see an improvement in terms of the resource usage of all the other players in the system.
Ron: I would agree with that. I would just say though that if you make the Web server that is hosting these Web services more resource efficient, maybe all you’re going to do is enable it to get more requests in queue the more quickly. Ultimately, this solution I think is going to solve a lot of problems related to time outs and server busy errors and that sort of thing, thread contentions, but not likely to increase overall performance.
But I definitely agree though. I would move this solution forward to WCF. I used to be on the COM+ team. COM+ was rolled into WCF so that it would have similar capabilities for pooling, instancing behavior, transactional support, those sorts of things. I would definitely move that forward into WCF.
OK! So great answer, Udi. Thank you so much for being on this ARCast Rapid Response.
Number 2
Ron: Hey this is Ron Jacobs back with another ARCast.TV Rapid Response. Today I’m joined by Udi Dahan, the Software Simplist from Israel.
Udi, I’m looking at the MSDN Architecture Forum and here’s a question from “blast.” Blast says he’s looking for where to put business rules. He’s developing a WinForm application. He uses data sets as the data layer, he says. He’s thinking about business rules and where to put them.
He says obviously, the more organized and centralized business rules are, the better. He’s tempted to put the business rules in the UI layer especially with the type data set. It makes a lot of sense there but not all rules belong on the client. He says some rules belong on the server, perhaps in a trigger.
So he’s asking where do you put your rules? How do you think about this problem, Udi?
Udi: Well, it looks like what he’s doing here is developing a two-tier client that is using WinForms and using datasets and speaking directly to the database. That in essence is part of his problem in that in terms of performance, he’d like to run more rules in the UI layer so that the user won’t be sending garbage to the database.
He also understands that because he’s building a multi-user system, there is a limited capability, in terms of concurrency, of actually having all the rules run correctly in order to make sure that everything is correct. So, his choice of an architecture, working two-tier is the main problem of why he has to fragment his business rules.
If he were to move towards a three-tier solution, that is put an application server between his smart client and the database, it would be a lot easier to put those business rules there. Now, once the business rules are out of the database, because again, we don’t have to deal with the concurrency issues once we have an application server and we’re using transactions there and we don’t have any disconnected problems, then what we can do is use those same DLLs, that same CLR code that runs the business rules, and deploy it client-side and use it there.
So, in terms of deployment, what we’d have is we’d have the same rules, both running client-side and server-side, whereas from a development perspective, we’d have them organized and centralized. That’s the way that I’d go about it.
Ron: Yeah, you know, I think conceptually I agree with you that a multi-tier solution would be a very good idea here. What I would probably think about conceptually, is breaking down rules into things that really ought to happen on the client-side. In particular, rules related to validation of data, so you know that you’ve got good and complete data before you ship it off to the server-side. Oftentimes you have to do that anyway because you have a button that shouldn’t be enabled until the data is valid, or something like that.
Udi: Absolutely.
Ron: Of course, we all know that if you have middle-tier web services, you must do validation both on the client-side and the server-side, because you must ensure that the valid data is received on the web server. So I agree with you that creating an assembly that you deploy on both sides is a good idea.
I would just expand on what you said a little bit and think about maybe on the server-side using a workflow foundation and business rules and workflow as a way to handle a lot of the heavier lifting, server-side validations and business rules that might require maybe sifting through more data or whatever kind of things, but server-side business rules that are more oriented towards business logic, and even if you have very, very data-intensive roles, then maybe some of those might even happen in the database. Don’t you agree?
Udi: Oh, absolutely. Absolutely. That’s something that I think often gets swept under the rug too much. Things like unique constraints and things like that are kinds of business rules. They protect the referential integrity and if we look at the alternatives, sometimes getting 10 million rows out of the database, in order to do some sort of unique email validation upon them, that’s just going to kill your performance.
There are certain things that it just makes sense to do them in the database, it’s just the best way to do it. The hard part, from a development perspective, is maintaining the coherence of your business rules. When you say, “OK, I want a single perspective, what are all the rules in my system?”
Even though we might try to keep it all CLR based, some of the things like unique constraints, like referential integrity, will be in the database. So, what I sometimes suggest to do is to have a separate solution, in terms of your development team, where you put all your business rules.
This includes both the SQL statements for defining your unique constraints and your referential integrity. Also put in that validation logic, your workflow that you’re going to be running server-side. If it’s AJAX controls and regular expressions that you’re going to be doing client-side in order to validate that data, absolutely make sure you have, from a development perspective, one place where you can go where you can see everything, because if you don’t do that [inaudible] can be running, and when things stop working, you won’t know how to debug it.
Ron: All right. Well, excellent answer. Udi, thank you so much.
Posted in Architecture, MSMQ, Podcast, Scalability, WCF, Web Services | No Comments »
Saturday, December 29th, 2007
The other day I was at Juval’s presentation where the main message was WCF is a better .NET. In other words, if you use WCF on every one of your classes, you’ll benefit. I don’t know about you, but I’m quite wary of silver bullets – they tend to inflict quite a bit of pain when used indiscriminately. This post is my response to all the people who came up to me at the end of the presentation and wanted to know if I agreed with these far-reaching architectural statements.
First of all let me say that Juval is indeed a master presenter. The “looks like a class, walks like a class, quacks like a class” bit was excellent. I could tell that most people didn’t notice the speedy hands quickly deleting all attributes from the classes before the “looks like a class…” bit. At times, I got flashbacks from the Wizard of Oz – “pay no attention to the man behind the curtain”. If all attributes in WCF only went on the interfaces, then this might actually fly, but we all know that that’s not the case.
One of the interesting comparisons Juval made with WCF was the introduction of .NET. Few people in the audience seemed to remember (or maybe were just professionally younger than .NET’s 8 years), but when it came out .NET was marketed as being mainly about XML Web Services. Juval stated that this was done to play down the fact that .NET made the previous Windows programming technologies obsolete. He then drew the same conclusion about WCF – that it’s as much .NET 3.0 as .NET was the next version of MFC; besides being written in a language that resembles the previous technology, it’s really all different. I don’t think that anyone would argue the difference, but is it really a “plain .NET” killer?
The answer seemed to come around the overhead of WCF – yet Juval deftly deflected that issue with a demo showing WCF doing 200 calls a second. And everybody just bought it – I was shocked. That’s 5ms per call. If you actually take Juval’s advice and use WCF on all your classes, you’ve bought yourself one hell of a performance nightmare. Say you have around 20 of your objects involved in a sequence to handle a user action – not that many actually. With a 5ms lag per object interaction, that user action is going to take 100ms – not including any database or webservice stuff you might be doing. If you do that in a server environment, you’ll be doing roughly 10 concurrent users per core. And that’s not even doing any heavy calculations or anything. Moderately sized systems are running upwards of 1000 concurrent users – if they needed 100 cores (or dozens of servers) for that, I’m guessing that they’d be out of business.
Let’s cut this short – WCF everywhere doesn’t scale, doesn’t perform, isn’t maintainable, or testable either. In other words – don’t do it. I know Juval is a brilliant guy, and an amazing presenter – but I don’t believe he would be employing this with his own clients. This actually bears repeating. WCF is a fine technology for your application’s boundaries, but don’t be pushing it in.
Don’t do it.
Posted in Architecture, Development, Performance, Scalability, WCF | 32 Comments »
Monday, December 17th, 2007
As a part of my efforts to make clearer what place nServiceBus has in the Microsoft .NET ecosystem, I’ve decided to retire the term “workflow”. Almost every conversation about nServiceBus where the term “workflow” was brought up, the reaction was almost identical:
“What’s wrong with Workflow Foundation? Why aren’t you using it like you use WCF?”
There’s nothing wrong with Workflow Foundation. The thing is that nServiceBus doesn’t really need workflow in the general sense of the term. An older term that’s been used in the DBMS community might make more sense – “long-lived transactions”. You see, nServiceBus requires state management over many messaging interactions, and thus, some kind of long-lived transaction to maintain consistency.
In 1987, a different model was introduced for handling these scenarios – the Saga [GARCIA-MOLINA 87], and was further expanded in 1992 [CHRYSANTHIS 92] to allow the saga to commit if a non-vital subset of the sub-transactions abort. This is what is used in nServiceBus.
When used in distributed manner on top of one-way messaging, this results in a solution where each service runs its own “mini-workflow”, and coordinates its actions with other services via messages. This integration style is different from the traditional broker, man-in-the-middle approach found in products like Biztalk; and is known as “choreography”, and is in the process of standardization in the WS-* specs, known as WS-Choreography.
So, the bottom line is that the source, examples, and documentation of nServiceBus is being moved in this direction. The source and examples on the sourceforge site have already been brought forward. This is a breaking change.
I hope that this will make it clearer that nServiceBus is a higher-level set of abstractions than WCF/WF – limiting the generality found in these frameworks to enable one cohesive way of working that will result in a solution that is both scalable and robust. On the other hand, nServiceBus is not a fully integrated product like Biztalk and intends to tackle different kinds of problems.
Bigger than a WCF/WF, smaller than a breadbox Biztalk.
Posted in ESB, NServiceBus, SOA, WCF, Workflow | 6 Comments »
Sunday, December 9th, 2007
I got this question the other day from one of my long-time readers Bill about nServiceBus and I thought I’d share:
I have a question around processing of messages in proper order. When leveraging multiple threads to process messages in a message queue, it is possible for the second message in the queue to get processed before the first – especially if the first message is considerably larger than the second. I have taken a lot of care to make sure that messages are sent in the correct order, only to find that the receiving system can process them out of order anyway.
Consider a Policy Created notification, which must come before a Policy Approved notification. If both messages are sitting in the queue when the receiving service starts up, the approval message can be processed before the creation message. How can I make sure that message ordering is respected by the receiving system? I am using WCF/MSMQ as the underlying transport by the way. The only way I have found so far is to limit the receiving service to a single thread, which is by no means desirable.
Well, the solution is really quite simple (at first).
If you’ve received a message that you think has arrived out of order, just call:
this.bus.HandleCurrentMessageLater();
and that will put the message back at the end of the queue.
Once you start considering the fact that you don’t know when the first message is supposed to arrive, you might turn to using a workflow to handle the logic. The workflow would store the policy id, and then allow for N round-trips, before it decided that something bad had happened (like the Policy Created message getting lost), and then it could forward that to an operator, or possibly contact the first system and ask for a replay of the policy created message – or whatever automated fault resolution protocol you like.
In other words, message ordering is probably more trouble than its worth.
Posted in Architecture, EDA, ESB, MSMQ, NServiceBus, Pub/Sub, WCF, Workflow | 10 Comments »
Tuesday, October 23rd, 2007
In this podcast we’ll look at the issues around Durable Services, what makes them stateful or stateless, as well as how WCF and WF can be used to implement them. Finally, we’ll compare solutions based on .NET 3.5 and on NServiceBus–covering aspects such as transactions and persistent time-outs.
Suresh asks:
Hi Udi,
I’ve been reading about the coming “durable services” that will be available with the next version of WCF. I also have been listening to your podcasts and reading your blog posts about NServiceBus where you talk about long-running workflows. It sounds like both of these technologies are trying to solve the same problem.
Do durable services do away with long-running workflow? If so, does that mean we don’t need Workflow Foundation either? If not, what is the connection between them.
If you could shed some light on the matter that would be great.
Suresh
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Additional References
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Posted in Architecture, Ask Udi Podcast, NServiceBus, Scalability, SOA, WCF, Web Services, Workflow | No Comments »
Thursday, August 30th, 2007
After trying a bunch of different directions it appears like I’ve found one that works. I didn’t think that I could make use of the top ServiceModel stuff, but I was wrong. Many thanks to Tomas Restrepo for making me rethink my basic assumptions.
I’ve also put in a bit of effort in setting up a bunch of configuration files allowing you to try the various transports for the example code. Please go through the Readme as it contains the detailed instructions. There are currently config files setting up non-WCF MSMQ, NetTCP, Basic HTTP, and WS Dual.
If you do go the MSMQ route, the example will run the long-running workflow code. The reason the example code won’t do that for the WCF cases is that I haven’t figured out yet the best way for a service to send a message back to itself, especially for the connected bindings. Any thoughts on this would be most appreciated.
Also, I’m open to hearing what directions you think the next version should go in. I’m currently thinking about including message transformation. Either that are doing a Multicast bus over a UDP transport.
This is a non-backwards-compatible update. In order to propertly integrate with the WCF philosophy I had to change the ITransport interface for Unicast transports. The meaning of this change is that transports are now expected to do their own threading and transaction management, while the bus object now joins the context that comes from the transport.
Download here.
Posted in ESB, MSMQ, NServiceBus, Pub/Sub, SOA, WCF, Web Services, Workflow | No Comments »
Tuesday, August 28th, 2007
I’m in the process of implementing a generic WCF transport for NServiceBus and am seriously going out of my mind. The fact that I have to do crazy reflection over generics to get around some of the channel model is ludicrous. To top it off, I now find out that there isn’t a simple generic way to send messages.
IOutputChannel exposes “void Send(Message message);” while IRequestChannel exposes “Message Request(Message message);”. Of course, they are incompatible having only an anorexic common interface IChannel (which exposes only “T GetProperty<T>() where T: class;”).
I’m doing everything in power to hide the complexity (sorry, flexibility) of WCF behind the simple IBus interface, but it looks like it’s going to bubble up in the configuration anyway.
If push comes to shove, I’ll just implement a bunch of my own transports which will specifically encapsulate each of the WCF bindings.
New release coming soon.
Posted in NServiceBus, Simplicity, WCF | No Comments »
Tuesday, July 17th, 2007
This week we return to the topic of Entity, Activity, and Process services and compares their usages as top-level SOA elements and as implementation details of the application architecture inside a business service.
And the question that this answers is:
Hi Udi,
We’ve been having some discussions about how to implement our latest project using SOA and this is what we came up with:
Every activity is a method, which is broken into a class ( Think separation of concerns ), so we get high reusability.
On top of those classes we have decided to put a WCF layer, so you can expose the method as a web method. If an activity needs data, then it will access a entity service via WCF. To make the activities useful for the business we put them in a class which we have called processes ( a process layer). A process contains one or more activities and is able to call other processes and activities aren’t allowed to call processes or other activities. On top of each process we have decided to put a WCF so the UI can access them.
So it’s pretty close to what you wrote about in the Microsoft Architecture Journal except that we don’t have direct call to the entity services, we wrap it up in an activity before the call, which is wrapped in a WCF-host. Much like the definitions in Ontology and Taxonomy of Services in a Service-Oriented Architecture
I would love to hear your comments and thoughts about this architecture.
With thanks, Ingo
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Posted in Ask Udi Podcast, Autonomous Services, ESB, SOA, WCF, Web Services | No Comments »
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“Udi, one of the great minds in this area. A man I respect immensely.”
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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, .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, 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, 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, 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, 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, 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, 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, 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, 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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