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Archive for the ‘Web Services’ Category



Web Service to NServiceBus Integration Sample

Sunday, December 16th, 2007

After receiving numerous requests to see how to expose a synchronous web service that communicates asynchronously with other services via nServiceBus, I’ve finally got a sample up.

I’ve included a direct link here for convenience (webservicebridge.zip).

In this sample, we have a service communicating over msmq, receiving a request message, and based on the value of the Id in that message, return either a success or fail result.

A regular web service makes use of that nServiceBus service in order to expose a synchronous API: “ErrorCodes Process(Request r);”

The implementation of the synchronous web service does some threading stuff to bridge the synchronous and asynchronous worlds.

And last, we have a regular web app which makes use of the synchronous web service.

____

I’ve also opened a discussion group for nServiceBus on Yahoo Groups, so you can find that here:

http://tech.groups.yahoo.com/group/nservicebus/

I’m going to try to take the information from the email exchanges I’ve been having and put them up so that the broader user base can take advantage of it. I won’t be putting up who sent me the email, or any identifying characteristics either of them or their employers, partners, etc.

Please send further questions about nServiceBus via the discussion group. Specific consultations can continue being sent directly to me – consult@UdiDahan.com.

Finally, if you have any ideas or suggestions for taking nServiceBus forward, please don’t hesitate to send them my way via the discussion group.

Thanks.



[Podcast] Migrating from N-Tier to SOA

Wednesday, December 5th, 2007

In this podcast we’ll be discussing certain methodologies for migrating an architecture from N-Tier to SOA. We’ll see what parts can be used almost unchanged, and which N-Tier concepts have no place in this new, service-oriented world.

Ketan asks:

Hello Udi,

I am Ketan, working as Analyst Programmer in India. I want some information regarding SOA Architecture. I have visited several blogs and sites and I do have enough knowledge regarding technical terms of SOA. I have worked a lot in 3-tier mechanism a lot and now want to switch on SOA Architecture in Visual Studio 2005.

I read your blog post How to migrate to SOA and liked the contents and am interested in doing it. Can you please be more precise about how to migrate from 3-tier to SOA? Actually, I have read whole content of above link and you have explained enough. But, still I want you to keep me out from dark. You have described it functionally, but I want some technical description of this process. Please help me in this.

If you can provide me some example/application (in which SOA Architecture has been implemented), then it will be very helpful to me.

Thanks in advance. Waiting for your favorable reply.

Ketan

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Asynchronous, High-Performance Login for Web Farms

Saturday, November 10th, 2007

Often during my consulting engagements I run into people who say, "some things just can’t be made asynchronous" even after they agree about the inherent scalability that asynchronous communications pattern bring. One often-cited example is user authentication – taking a username and password combo and authenticating it against some back-end store. For the purpose of this post, I’m going to assume a database. Also, I’m not going to be showing more advanced features like ETags to further improve the solution.

The Setup

Just so that the example is in itself secure, we’ll assume that the password is one-way hashed before being stored. Also, given a reasonable network infrastructure our web servers will be isolated in the DMZ and will have to access some application server which, in turn, will communicate with the DB. There’s also a good chance for something like round-robin load-balancing between web servers, especially for things like user login.

Before diving into the meat of it, I wanted to preface with a few words. One of the commonalities I’ve found when people dismiss asynchrony is that they don’t consider a real deployment environment, or scaling up a solution to multiple servers, farms, or datacenters.

The Synchronous Solution

In the synchronous solution, each one of our web servers will be contacting the app server for each user login request. In other words, the load on the app server and, consequently, on the database server will be proportional to the number of logins. One property of this load is its data locality, or rather, the lack of it. Given that user U logged in, the DB won’t necessarily gain any performance benefits by loading all username/password data into memory for the same page as user U. Another property is that this data is very non-volatile – it doesn’t change that often.

I won’t go to far into the synchronous solution since its been analysed numerous times before. The bottom line is that the database is the bottleneck. You could use sharding solutions. Many of the large sites have numerous read-only databases for this kind of data, with one master for updates – replicating out to the read-only replicas. That’s great if you’re using a nice cheap database like mySql (of LAMP), not so nice if you’re running Oracle or MS Sql Server.

Regardless of what you’re doing in your data tier, you’re there. Wouldn’t it be nice to close the loop in the web servers? Even if you are using Apache, that’s going to be less iron, electricity, and cooling all around. That’s what the asynchronous solution is all about – capitalizing on the low cost of memory to save on other things.

The Asynchronous Solution

In the asynchronous solution, we cache username/hashed-password pairs in memory on our web servers, and authenticate against that. Let’s analyse how much memory that takes:

Usernames are usually 12 characters or less, but let’s take an average of 32 to be sure. Using Unicode we get to 64 bytes for the username. Hashed passwords can run between 256 and 512 bits depending on the algorithm, divide by 8 and you have 64 bytes. That’s about 128 bytes altogether. So we can safely cache 8 million of these with 1GB of memory per web server. If you’ve got a million users, first of all, good for you :) Second, that’s just 128 MB of memory – relatively nothing even for a cheap 2GB web server.

Also, consider the fact that when registering a new user we can check if such a username is already taken at the web server level. That doesn’t mean it won’t be checked again in the DB to account for concurrency issues, but that the load on the DB is further reduced. Other things to notice include no read-only replicas and no replication. Simple. Our web servers are the "replicas".

The Authentication Service

What makes it all work is the "Authentication Service" on the app server. This was always there in the synchronous solution. It is what used to field all the login requests from the web servers, and, of course, allowed them to register new users and all the regular stuff. The difference is that now it publishes a message when a new user is registered (or rather, is validated – all a part of the internal long-running workflow). It also allows subscribers to receive the list of all username/hashed-password pairs. It’s also quite likely that it would keep the same data in memory too.

The same message can be used to publish both single updates, and returning the full list when using NServiceBus. Let’s define the message:

[Serializable]
public class UsernameInUseMessage : IMessage
{
    private string username;
    public string Username
    {
        get { return username; }
        set { username = value; }
    }

    private byte[] hashedPassword;
    public byte[] HashedPassword
    {
        get { return hashedPassword; }
        set { hashedPassword = value; }
    }
}

And the message that the web server sends when it wants the full list:

[Serializable]
public class GetAllUsernamesMessage : IMessage
{

}

And the code that the web server runs on startup looks like this (assuming constructor injection):

 

public class UserAuthenticationServiceAgent

    public UserAuthenticationServiceAgent(IBus bus) 
    { 
        this.bus = bus;
        bus.Subscribe(typeof(UsernameInUseMessage)); 
        bus.Send(new GetAllUsernamesMessages());
    }

}

And the code that runs in the Authentication Service when the GetAllUsernamesMessage is received:

 

public class GetAllUsernamesMessageHandler : BaseMessageHandler<GetAllUsernamesMessage>
{
    public override void Handle(GetAllUsernamesMessage message)
    {
        this.Bus.Reply(Cache.GetAll<UsernameInUseMessage>());
    }
}

 

And the class on the web server that handles a UsernameInUseMessage when it arrives:

 

public class UsernameInUseMessageHandler : BaseMessageHandler<UsernameInUseMessage>
{
    public override void Handle(UsernameInUseMessage message)
    { 
        WebCache.SaveOrUpdate(message.Username, message.HashedPassword); 
    }
}

When the app server sends the full list, multiple objects of the type UsernameInUseMessage are sent in one physical message to that web server. However, the bus object that runs on the web server dispatches each of these logical messages one at a time to the message handler above.

So, when it comes time to actually authenticate a user, this the web page (or controller, if you’re doing MVC) would call:

public class UserAuthenticationServiceAgent
{
    public bool Authenticate(string username, string password)
    {
        byte[] existingHashedPassword = WebCache[username];
        if (existingHashedPassword != null)
            return existingHashedPassword == this.Hash(password);

        return false;
    }
}

 

When registering a new user, the web server would of course first check its cache, and then send a RegisterUserMessage that contained the username and the hashed password.

[Serializable]
[StartsWorkflow]
public class RegisterUserMessage : IMessage
{
    private string username;
    public string Username
    {
        get { return username; }
        set { username = value; }
    }

    private string email;
    public string Email
    {
        get { return email; }
        set { email = value; }
    }

    private byte[] hashedPassword;
    public byte[] HashedPassword
    {
        get { return hashedPassword; }
        set { hashedPassword = value; }
    }
}

 

When the RegisterUserMessage arrives at the app server, a new long-running workflow is kicked off to handle the process:

public class RegisterUserWorkflow :
    BaseWorkflow<RegisterUserMessage>, IMessageHandler<UserValidatedMessage>
{
    public void Handle(RegisterUserMessage message)
    {
        //send validation request to message.Email containing this.Id (a guid)
        // as a part of the URL
    }

    /// <summary>
    /// When a user clicks the validation link in the email, the web server
    /// sends this message (containing the workflow Id)
    /// </summary>
    /// <param name="message"></param>
    public void Handle(UserValidatedMessage message)
    {
        // write user to the DB

        this.Bus.Publish(new UsernameInUseMessage(
            message.Username, message.HashedPassword));
    }
}

That UsernameInUseMessage would eventually arrive at all the web servers subscribed.

Performance/Security Trade-Offs

When looking deeper into this workflow we realize that it could be implemented as two separate message handlers, and have the email address take the place of the workflow Id. The problem with this alternate, better performing solution has to do with security. By removing the dependence on the workflow Id, we’ve in essence stated that we’re willing to receive a UserValidatedMessage without having previously received the RegisterUserMessage.

Since the processing of the UserValidatedMessage is relatively expensive – writing to the DB and publishing messages to all web servers, a malicious user could perform a denial of service (DOS) attack without that many messages, thus flying under the radar of many detection systems. Spoofing a guid that would result in a valid workflow instance is much more difficult. Also, since workflow instances would probably be stored in some in-memory, replicated data grid the relative cost of a lookup would be quite small – small enough to avoid a DOS until a detection system picked it up.

Improved Bandwidth & Latency

The bottom line is that you’re getting much more out of your web tier this way, rather than hammering your data tier and having to scale it out much sooner. Also, notice that there is much less network traffic this way. Not such a big deal for usernames and passwords, but other scenarios built in the same way may need more data. Of course, the time it takes us to log a user in is much shorter as well since we don’t have to cross back and forth from the web server (in the DMZ) to the app server, to the db server.

The important thing to remember in this solution is doing pub/sub. NServiceBus merely provides a simple API for designing the system around pub/sub. And publishing is where you get the serious scalability. As you get more users, you’ll obviously need to get more web servers. The thing is that you probably won’t need more database servers just to handle logins. In this case, you also get lower latency per request since all work needed to be done can be done locally on the server that received the request.

ETags make it even better

For the more advanced crowd, I’ll wrap it up with the ETags. Since web servers do go down, and the cache will be cleared, what we can do is to write that cache to disk (probably in a background thread), and "tag" it with something that the server gave us along with the last UsernameInUseMessage we received. That way, when the web server comes back up, it can send that ETag along with its GetAllUsernamesMessage so that the app server will only send the changes that occurred since. This drives down network usage even more at the insignificant cost of some disk space on the web servers.

And in closing…

Even if you don’t have anything more than a single physical server today, and it acts as your web server and database server, this solution won’t slow things down. If anything, it’ll speed it up. Regardless, you’re much better prepared to scale out than before – no need to rip and replace your entire architecture just as you get 8 million Facebook users banging down your front door.

So, go check out NServiceBus and get the most out of your iron.



[Podcast] Versioning and SOA–There is no IDog2

Friday, November 9th, 2007

In this podcast we’ll look at the issues around versioning and SOA and how the asynchronous nature of messaging obviates the need for previously accepted interface-based versioning practices.

Jarrod asks:

Hi Udi,

I have some questions around versioning and SOA:

Over the years I’ve been fairly adamant about the practice of versioning interfaces should a method change be needed.

Hence, IDog and IDog2

Generally I would also say that a method addition would need a new interface as much as a change to an existing method or property (sometimes requiring completely deprecating the old interface).

With SOA being used more and contract first designs coming down the pipe…an addition of a method or operation to a contract in SOA does not mean its a breaking change.

So, do you continue to create a new interface and version the name within an SOA environment? Even if its just one method that is being added?

A service contract, in general…with just a single method in my opinion is a bad design. Sure, there are exceptions to that but I can just see changes made to the service contracts over the course of a few years with many 1-2 method interfaces.

Day 1 : 12 methods on interface IDog

6 months later : 1 new method, create IDog2 which implements IDog

15 months later : 2 new methods, create IDog3 which implements IDog2

Some can argue that if you’re having to add methods like this, the original design was flawed. That may be…or you could just be in a volatile business environment in which SOA must adapt.

So my main questions are:

1) Do you think its the best practice to continue to version interfaces for non-breaking method additions in an SOA environment in which you also have control of the consumers (internal consumers)?

2) Do you think its the best practice to continue to version interfaces for non-breaking method additions in an SOA environment in which you do not have control of the consumers (external consumers)?

3) If the answer to the above is yes, is a single method on a new interface acceptable?

4) If you know of a problem in an existing interface on a method and have control of the consumers – do you “fix” the method and redeploy to the consumers? Or do you deprecate the entire interface and begin anew?

I’m interested in seeing your responses :)

Jarrod

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[Podcast] Durable Services with WCF, WF, and NServiceBus

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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Or download directly here

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InfoQ interview on NServiceBus

Friday, September 7th, 2007

The good folks from InfoQ interviewed me recently about NServiceBus. You can find the full interview here.

Here are some choice tidbits:

“For any developer who architects using SOA principles, on the basis for using NServiceBus over some other methodology or some other so-called enterprise service bus:”

NServiceBus makes it difficult to work in ways that will hurt your scalability. Since the asynchronous messaging patterns are brought to the fore, developers will, by default, avoid the temporal coupling so prevalent in most Web Service implementations. Other methodologies make so many other options just as easy to use that developers can make mistakes that will hurt their scalability and availability and only find out about those mistakes in production .

Another thing NServiceBus does differently is to totally isolate all workflow code from all technologies. This makes it easy to unit-test workflow classes, making it possible to iterate quickly on the development of key business processes. These portable .NET POJOs give developers the flexibility to host their workflows in whatever runtime they want.

“Having noticed NServiceBus is built with MSMQ in mind or as an option, when asked why this choice of direction: ”

The core of NServiceBus is not dependent on MSMQ. The extensibility points of NServiceBus allow you to plug in your own communication transport, subscription storage, and workflow persister. I’ve already implemented a transport over MSMQ, and another over WCF’s NetTCP binding. Developers can use those as-is or write their own. Many of the SOA products currently out there are much more tied to HTTP, so this is something of a break from the common practice.

I chose to use MSMQ since it is one of the two main Microsoft communications technologies that enables parties to communicate in a disconnected fashion (SQL Server Service Broker is the other). MSMQ has a much more accessible API in that it is directly available as a part of the .NET Framework whereas Service Broker currently isn’t. I consider disconnected communications a critical part of any SOA infrastructure since the Tenet of Service Autonomy does not allow us to assume that the service with which we wish to communicate is currently available.

Is there anything you’d like to know about NServiceBus? Drop me a comment below.

Thanks.



Generic WCF Transport available for NServiceBus

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.



NServiceBus Distributed Topology Q&A

Saturday, August 25th, 2007

I’ve been receiving more and more questions about how NServiceBus fits in distributed systems and wanted to share them:

My question is about distributed topology.

The EAI-hub-and-spoke model is all about the central server. It’s useful sometimes, but there are a lot of reasons why I’m not gung-ho on using a hub as the center of the integration universe.

The ESB distributed model puts code on the endpoints. That code solves some of the messaging problems that apps face, so that apps don’t have to face them. It also solves some of the messaging problems that enterprises face, so that enterprises don’t have to face them. (I need both).

Those problems include simple coding and deployment model, pub-sub routing, reliable transport, simple transformation, and orchestration. I wonder which of these you can do in your tool, and which you are planning to do.

I’m also interested in management. How do you insure that the endpoints are correctly configured? Do you have a central configuration store? How do you propagate changes from the center to the messaging endpoints?

And here’s my response:

The important parts of NServiceBus that are independent of the distributed topology are the API and the connection to long-running workflow. This code is indeed on the endpoint. However, if you wanted to you could easily connect to something like BizTalk and do whatever you wanted there. This general idea though is to support the ESB distributed model since there’s no such things as a centralized ESB.

In terms of the capabilities you’ve mentioned, I’ve seen developers pick up the coding model in a day or two. The deployment model is just a bunch of DLLs you deploy with each endpoint. Dependency Injection is supported by www.SpringFramework.net but you can replace that with something else easily as another implementation of the ObjectBuilder interfaces.

Currently pub/sub routing is supported over regular point-to-point transports in a transport agnostic way. You also have the ability to have subscriptions be persisted so that even if a server restarts (and clients don’t, and can’t know about that) all the subscriptions will be remembered.

The reliable transport that is currently supported is MSMQ, with the option of defining per-message type if you want durable messaging (using the [Recoverable] attribute).

In terms of orchestration you get a nice model for long-running workflow that gets kicked off by messages decorated with the [StartsWorkflow] attribute, and messages that implement the IWorkflowMessage interface get automatically routed to the persistent workflow instance. You have the ability to change the storage of workflow instances easily as well. Workflows are simple classes which are easily unit-testable in that they expose a “void Handle(T message);” method for every message type (T) that is involved in the workflow.

I haven’t done anything in terms of simple transformation yet but am currently looking for the right place in the message processing pipeline to put it. I also haven’t done anything yet in terms of management.

What is currently being done management-wise on the projects that use it are the commercial options for managing configuration files in distributed environments coupled with the regular ability to restart windows services and IIS applications. I haven’t seen anything lacking in that solution yet.


If you have any questions, please don’t hesitate to send them my way – NServiceBus@UdiDahan.com.



Why I wrote NServiceBus

Saturday, August 25th, 2007

I’ve been asked if I have a document describing the architecture of NServiceBus, so since I don’t have one yet, this post will be the start.

First of all, there were two major forces that drove me to write NServiceBus. First of all I wanted to formalize the way Service Layer classes were written when using asynchronous messaging (regardless of Web Services). And second I wanted to formalize a communications API which supported pub/sub so that I could freely move between transports – whether they inherently supported pub/sub or not (the fact that Indigo did not falls under this).

From there it was filling in the details. Until finally I made the step to formalize the way long-running workflow connects to asynchronous messaging. That’s the third pillar as far as I’m concerned about ESBs. Using MSMQ I do enable Shared Subscriptions like Sonic does.

I try to stay away from the vendor side of ESB definitions and just deal with what capabilities such a library should provide. As such, it is inherently distributed – running on each server/client.



Using NServiceBus from a Win/Web Client

Tuesday, August 21st, 2007

Here’s another question I’ve received about how to use NServiceBus in various architectures. Sai asks:

1. In a webservice scenario, Is it the webservice which is the client?
2. Will a bus locate the WS or WS locate the bus?
3. How will the WS pass a message to the bus?
4. How will a WS subscribe to a bus?
5. Will it be possible to show an example project where you are using a WS and a bus and a WinForm/WebForm as the client?

1. The answer is a bit dependent on how you use web services today. If you don’t care about the client of your webservice (as in you have a public web service), then yes, the web service would be the client in my example. If you are using web services today to connect your win client to a back end server, then you would in essence be replacing the classic web service stack with NServiceBus, possibly using an implementation of ITransport which uses web services for transporting the messages.

2. The “bus” object which you use to communicate does not need to be “located”. Its just a regular object you use within your process on the same thread as your regular code. If the bus needs to communicate with a regular web service, you would use a transport that supports web services as stated above. In the configuration of such a transport object you would probably include the URI of the web service.

3. Sending a message is just creating an instance of a class which implements the IMessage interface and calling the “Send” method on the bus object.

4. You have to look at a web service as just some code that is running in a process hosted by IIS – therefore subscribing to message types is the same as in the example code. The important part to understand is what it means to subscribe to a message type. All it means is that when the publisher will call the “Publish” method on his end, a message will be sent to the endpoint your bus is listening on. When that message arrives, the bus will attempt to dispatch it to a message handler. If you don’t have a message handler which can handle that message type, nothing will happen.

5. I’ll get an example up soon. In a web client scenario, your ASP.NET application would be the client shown in the example code.

Please feel free to send me questions, either in the comments or to NServiceBus@UdiDahan.com. I’m more than happy to answer them.



   


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I am honored to have Udi as a colleague and a friend (plus having his cell phone on my speed dial).”

Ward Bell Ward Bell, VP Product Development at IdeaBlade
“Everyone will tell you how smart and knowledgable Udi is ... and they are oh-so-right. Let me add that Udi is a smart LISTENER. He's always calibrating what he has to offer with your needs and your experience ... looking for the fit. He has strongly held views ... and the ability to temper them with the nuances of the situation.
I trust Udi to tell me what I need to hear, even if I don't want to hear it, ... in a way that I can hear it. That's a rare skill to go along with his command and intelligence.”

Eli Brin, Program Manager at RISCO Group
“We hired Udi as a SOA specialist for a large scale project. The development is outsourced to India. SOA is a buzzword used almost for anything today. We wanted to understand what SOA really is, and what is the meaning and practice to develop a SOA based system.
We identified Udi as the one that can put some sense and order in our minds. We started with a private customized SOA training for the entire team in Israel. After that I had several focused sessions regarding our architecture and design.
I will summarize it simply (as he is the software simplist): We are very happy to have Udi in our project. It has a great benefit. We feel good and assured with the knowledge and practice he brings. He doesn’t talk over our heads. We assimilated nServicebus as the ESB of the project. I highly recommend you to bring Udi into your project.”

Catherine Hole Catherine Hole, Senior Project Manager at the Norwegian Health Network
“My colleagues and I have spent five interesting days with Udi - diving into the many aspects of SOA. Udi has shown impressive abilities of understanding organizational challenges, and has brought the business perspective into our way of looking at services. He has an excellent understanding of the many layers from business at the top to the technical infrstructure at the bottom. He is a great listener, and manages to simplify challenges in a way that is understandable both for developers and CEOs, and all the specialists in between.”

Yoel Arnon Yoel Arnon, MSMQ Expert
“Udi has a unique, in depth understanding of service oriented architecture and how it should be used in the real world, combined with excellent presentation skills. I think Udi should be a premier choice for a consultant or architect of distributed systems.”

Vadim Mesonzhnik, Development Project Lead at Polycom
“When we were faced with a task of creating a high performance server for a video-tele conferencing domain we decided to opt for a stateless cluster with SQL server approach. In order to confirm our decision we invited Udi.

After carefully listening for 2 hours he said: "With your kind of high availability and performance requirements you don’t want to go with stateless architecture."

One simple sentence saved us from implementing a wrong product and finding that out after years of development. No matter whether our former decisions were confirmed or altered, it gave us great confidence to move forward relying on the experience, industry best-practices and time-proven techniques that Udi shared with us.
It was a distinct pleasure and a unique opportunity to learn from someone who is among the best at what he does.”

Jack Van Hoof Jack Van Hoof, Enterprise Integration Architect at Dutch Railways
“Udi is a respected visionary on SOA and EDA, whose opinion I most of the time (if not always) highly agree with. The nice thing about Udi is that he is able to explain architectural concepts in terms of practical code-level examples.”

Neil Robbins Neil Robbins, Applications Architect at Brit Insurance
“Having followed Udi's blog and other writings for a number of years I attended Udi's two day course on 'Loosely Coupled Messaging with NServiceBus' at SkillsMatter, London.

I would strongly recommend this course to anyone with an interest in how to develop IT systems which provide immediate and future fitness for purpose. An influential and innovative thought leader and practitioner in his field, Udi demonstrates and shares a phenomenally in depth knowledge that proves his position as one of the premier experts in his field globally.

The course has enhanced my knowledge and skills in ways that I am able to immediately apply to provide benefits to my employer. Additionally though I will be able to build upon what I learned in my 2 days with Udi and have no doubt that it will only enhance my future career.

I cannot recommend Udi, and his courses, highly enough.”

Nick Malik Nick Malik, Enterprise Architect at Microsoft Corporation
You are an excellent speaker and trainer, Udi, and I've had the fortunate experience of having attended one of your presentations. I believe that you are a knowledgable and intelligent man.”

Sean Farmar Sean Farmar, Chief Technical Architect at Candidate Manager Ltd
“Udi has provided us with guidance in system architecture and supports our implementation of NServiceBus in our core business application.

He accompanied us in all stages of our development cycle and helped us put vision into real life distributed scalable software. He brought fresh thinking, great in depth of understanding software, and ongoing support that proved as valuable and cost effective.

Udi has the unique ability to analyze the business problem and come up with a simple and elegant solution for the code and the business alike.
With Udi's attention to details, and knowledge we avoided pit falls that would cost us dearly.”

Børge Hansen Børge Hansen, Architect Advisor at Microsoft
“Udi delivered a 5 hour long workshop on SOA for aspiring architects in Norway. While keeping everyone awake and excited Udi gave us some great insights and really delivered on making complex software challenges simple. Truly the software simplist.”

Motty Cohen, SW Manager at KorenTec Technologies
“I know Udi very well from our mutual work at KorenTec. During the analysis and design of a complex, distributed C4I system - where the basic concepts of NServiceBus start to emerge - I gained a lot of "Udi's hours" so I can surely say that he is a professional, skilled architect with fresh ideas and unique perspective for solving complex architecture challenges. His ideas, concepts and parts of the artifacts are the basis of several state-of-the-art C4I systems that I was involved in their architecture design.”

Aaron Jensen Aaron Jensen, VP of Engineering at Eleutian Technology
Awesome. Just awesome.

We’d been meaning to delve into messaging at Eleutian after multiple discussions with and blog posts from Greg Young and Udi Dahan in the past. We weren’t entirely sure where to start, how to start, what tools to use, how to use them, etc. Being able to sit in a room with Udi for an entire week while he described exactly how, why and what he does to tackle a massive enterprise system was invaluable to say the least.

We now have a much better direction and, more importantly, have the confidence we need to start introducing these powerful concepts into production at Eleutian.”

Gad Rosenthal Gad Rosenthal, Department Manager at Retalix
“A thinking person. Brought fresh and valuable ideas that helped us in architecting our product. When recommending a solution he supports it with evidence and detail so you can successfully act based on it. Udi's support "comes on all levels" - As the solution architect through to the detailed class design. Trustworthy!”

Chris Bilson Chris Bilson, Developer at Russell Investment Group
“I had the pleasure of attending a workshop Udi led at the Seattle ALT.NET conference in February 2009. I have been reading Udi's articles and listening to his podcasts for a long time and have always looked to him as a source of advice on software architecture.
When I actually met him and talked to him I was even more impressed. Not only is Udi an extremely likable person, he's got that rare gift of being able to explain complex concepts and ideas in a way that is easy to understand.
All the attendees of the workshop greatly appreciate the time he spent with us and the amazing insights into service oriented architecture he shared with us.”

Alexey Shestialtynov Alexey Shestialtynov, Senior .Net Developer at Candidate Manager
“I met Udi at Candidate Manager where he was brought in part-time as a consultant to help the company make its flagship product more scalable. For me, even after 30 years in software development, working with Udi was a great learning experience. I simply love his fresh ideas and architecture insights.
As we all know it is not enough to be armed with best tools and technologies to be successful in software - there is still human factor involved. When, as it happens, the project got in trouble, management asked Udi to step into a leadership role and bring it back on track. This he did in the span of a month. I can only wish that things had been done this way from the very beginning.
I look forward to working with Udi again in the future.”

Christopher Bennage Christopher Bennage, President at Blue Spire Consulting, Inc.
“My company was hired to be the primary development team for a large scale and highly distributed application. Since these are not necessarily everyday requirements, we wanted to bring in some additional expertise. We chose Udi because of his blogging, podcasting, and speaking. We asked him to to review our architectural strategy as well as the overall viability of project.
I was very impressed, as Udi demonstrated a broad understanding of the sorts of problems we would face. His advice was honest and unbiased and very pragmatic. Whenever I questioned him on particular points, he was able to backup his opinion with real life examples. I was also impressed with his clarity and precision. He was very careful to untangle the meaning of words that might be overloaded or otherwise confusing. While Udi's hourly rate may not be the cheapest, the ROI is undoubtedly a deal. I would highly recommend consulting with Udi.”

Robert Lewkovich, Product / Development Manager at Eggs Overnight
“Udi's advice and consulting were a huge time saver for the project I'm responsible for. The $ spent were well worth it and provided me with a more complete understanding of nServiceBus and most importantly in helping make the correct architectural decisions earlier thereby reducing later, and more expensive, rework.”

Ray Houston Ray Houston, Director of Development at TOPAZ Technologies
“Udi's SOA class made me smart - it was awesome.

The class was very well put together. The materials were clear and concise and Udi did a fantastic job presenting it. It was a good mixture of lecture, coding, and question and answer. I fully expected that I would be taking notes like crazy, but it was so well laid out that the only thing I wrote down the entire course was what I wanted for lunch. Udi provided us with all the lecture materials and everyone has access to all of the samples which are in the nServiceBus trunk.

Now I know why Udi is the "Software Simplist." I was amazed to find that all the code and solutions were indeed very simple. The patterns that Udi presented keep things simple by isolating complexity so that it doesn't creep into your day to day code. The domain code looks the same if it's running in a single process or if it's running in 100 processes.”

Ian Cooper Ian Cooper, Team Lead at Beazley
“Udi is one of the leaders in the .Net development community, one of the truly smart guys who do not just get best architectural practice well enough to educate others but drives innovation. Udi consistently challenges my thinking in ways that make me better at what I do.”

Liron Levy, Team Leader at Rafael
“I've met Udi when I worked as a team leader in Rafael. One of the most senior managers there knew Udi because he was doing superb architecture job in another Rafael project and he recommended bringing him on board to help the project I was leading.
Udi brought with him fresh solutions and invaluable deep architecture insights. He is an authority on SOA (service oriented architecture) and this was a tremendous help in our project.
On the personal level - Udi is a great communicator and can persuade even the most difficult audiences (I was part of such an audience myself..) by bringing sound explanations that draw on his extensive knowledge in the software business. Working with Udi was a great learning experience for me, and I'll be happy to work with him again in the future.”

Adam Dymitruk Adam Dymitruk, Director of IT at Apara Systems
“I met Udi for the first time at DevTeach in Montreal back in early 2007. While Udi is usually involved in SOA subjects, his knowledge spans all of a software development company's concerns. I would not hesitate to recommend Udi for any company that needs excellent leadership, mentoring, problem solving, application of patterns, implementation of methodologies and straight out solution development.
There are very few people in the world that are as dedicated to their craft as Udi is to his. At ALT.NET Seattle, Udi explained many core ideas about SOA. The team that I brought with me found his workshop and other talks the highlight of the event and provided the most value to us and our organization. I am thrilled to have the opportunity to recommend him.”

Eytan Michaeli Eytan Michaeli, CTO Korentec
“Udi was responsible for a major project in the company, and as a chief architect designed a complex multi server C4I system with many innovations and excellent performance.”


Carl Kenne Carl Kenne, .Net Consultant at Dotway AB
“Udi's session "DDD in Enterprise apps" was truly an eye opener. Udi has a great ability to explain complex enterprise designs in a very comprehensive and inspiring way. I've seen several sessions on both DDD and SOA in the past, but Udi puts it in a completly new perspective and makes us understand what it's all really about. If you ever have a chance to see any of Udi's sessions in the future, take it!”

Avi Nehama, R&D Project Manager at Retalix
“Not only that Udi is a briliant software architecture consultant, he also has remarkable abilities to present complex ideas in a simple and concise manner, and...
always with a smile. Udi is indeed a top-league professional!”

Ben Scheirman Ben Scheirman, Lead Developer at CenterPoint Energy
“Udi is one of those rare people who not only deeply understands SOA and domain driven design, but also eloquently conveys that in an easy to grasp way. He is patient, polite, and easy to talk to. I'm extremely glad I came to his workshop on SOA.”

Scott C. Reynolds Scott C. Reynolds, Director of Software Engineering at CBLPath
“Udi is consistently advancing the state of thought in software architecture, service orientation, and domain modeling.
His mastery of the technologies and techniques is second to none, but he pairs that with a singular ability to listen and communicate effectively with all parties, technical and non, to help people arrive at context-appropriate solutions. Every time I have worked with Udi, or attended a talk of his, or just had a conversation with him I have come away from it enriched with new understanding about the ideas discussed.”

Evgeny-Hen Osipow, Head of R&D at PCLine
“Udi has helped PCLine on projects by implementing architectural blueprints demonstrating the value of simple design and code.”

Rhys Campbell Rhys Campbell, Owner at Artemis West
“For many years I have been following the works of Udi. His explanation of often complex design and architectural concepts are so cleanly broken down that even the most junior of architects can begin to understand these concepts. These concepts however tend to typify the "real world" problems we face daily so even the most experienced software expert will find himself in an "Aha!" moment when following Udi teachings.
It was a pleasure to finally meet Udi in Seattle Alt.Net OpenSpaces 2008, where I was pleasantly surprised at how down-to-earth and approachable he was. His depth and breadth of software knowledge also became apparent when discussion with his peers quickly dove deep in to the problems we current face. If given the opportunity to work with or recommend Udi I would quickly take that chance. When I think .Net Architecture, I think Udi.”

Sverre Hundeide Sverre Hundeide, Senior Consultant at Objectware
“Udi had been hired to present the third LEAP master class in Oslo. He is an well known international expert on enterprise software architecture and design, and is the author of the open source messaging framework nServiceBus. The entire class was based on discussion and interaction with the audience, and the only Power Point slide used was the one showing the agenda.
He started out with sketching a naive traditional n-tier application (big ball of mud), and based on suggestions from the audience we explored different solutions which might improve the solution. Whatever suggestions we threw at him, he always had a thoroughly considered answer describing pros and cons with the suggested solution. He obviously has a lot of experience with real world enterprise SOA applications.”

Raphaël Wouters Raphaël Wouters, Owner/Managing Partner at Medinternals
“I attended Udi's excellent course 'Advanced Distributed System Design with SOA and DDD' at Skillsmatter. Few people can truly claim such a high skill and expertise level, present it using a pragmatic, concrete no-nonsense approach and still stay reachable.”

Nimrod Peleg Nimrod Peleg, Lab Engineer at Technion IIT
“One of the best programmers and software engineer I've ever met, creative, knows how to design and implemet, very collaborative and finally - the applications he designed implemeted work for many years without any problems!

Jose Manuel Beas
“When I attended Udi's SOA Workshop, then it suddenly changed my view of what Service Oriented Architectures were all about. Udi explained complex concepts very clearly and created a very productive discussion environment where all the attendees could learn a lot. I strongly recommend hiring Udi.”

Daniel Jin Daniel Jin, Senior Lead Developer at PJM Interconnection
“Udi is one of the top SOA guru in the .NET space. He is always eager to help others by sharing his knowledge and experiences. His blog articles often offer deep insights and is a invaluable resource. I highly recommend him.”

Pasi Taive Pasi Taive, Chief Architect at Tieto
“I attended both of Udi's "UI Composition Key to SOA Success" and "DDD in Enterprise Apps" sessions and they were exceptionally good. I will definitely participate in his sessions again. Udi is a great presenter and has the ability to explain complex issues in a manner that everyone understands.”

Eran Sagi, Software Architect at HP
“So far, I heard about Service Oriented architecture all over. Everyone mentions it – the big buzz word. But, when I actually asked someone for what does it really mean, no one managed to give me a complete satisfied answer. Finally in his excellent course “Advanced Distributed Systems”, I got the answers I was looking for. Udi went over the different motivations (principles) of Services Oriented, explained them well one by one, and showed how each one could be technically addressed using NService bus. In his course, Udi also explain the way of thinking when coming to design a Service Oriented system. What are the questions you need to ask yourself in order to shape your system, place the logic in the right places for best Service Oriented system.

I would recommend this course for any architect or developer who deals with distributed system, but not only. In my work we do not have a real distributed system, but one PC which host both the UI application and the different services inside, all communicating via WCF. I found that many of the architecture principles and motivations of SOA apply for our system as well. Enough that you have SW partitioned into components and most of the principles becomes relevant to you as well. Bottom line – an excellent course recommended to any SW Architect, or any developer dealing with distributed system.”

Consult with Udi

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

97 Things Every Software Architect Should Know



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