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Archive for the ‘BizTalk’ Category

The Danger of Centralized Workflows

Wednesday, July 13th, 2011

It isn’t uncommon for me to have a client or student at one of my courses ask me about some kind of workflow tool. This could be Microsoft Workflow Foundation, BizTalk, K2, or some kind of BPEL/orchestration engine. The question usually revolves around using this tool for all workflows in the system as opposed to the SOA-EDA-style publish/subscribe approach I espouse.

The question

The main touted benefit of these workflow-centric architectures is that we don’t have to change the code of the system in order to change its behavior resulting in ultimate flexibility!

Some of you may have already gone down this path and are shaking your heads remembering how your particular road to hell was paved with the exact same good intentions.

Let me explain why these things tend to go horribly wrong.

What’s behind the curtain

It starts with the very nature of workflow – a flow chart, is procedural in nature. First do this, then that, if this, then that, etc. As we’ve experienced first hand in our industry, procedural programming is fine for smaller problems but isn’t powerful enough to handle larger problems. That’s why we’ve come up with object-oriented programming.

I have yet to see an object-oriented workflow drag-and-drop engine. Yes, it works great for simple demo-ware apps. But if you try to through your most complex and volatile business logic at it, it will become a big tangled ball of spaghetti – just like if you were using text rather than pictures to code it.

And that’s one of the fundamental fallacies about these tools – you are still writing code. The fact that it doesn’t look like the rest of your code doesn’t change that fact. Changing the definition of your workflow in the tool IS changing your code.

On productivity

Sometimes people mention how much more productive it would be to use these tools than to write the code “by hand”. Occasionally I hear about an attempt to have “the business” use these tools to change the workflows themselves – without the involvement of developers (“imagine how much faster we could go without those pesky developers!”).

For those of us who have experienced this first-hand, we know that’s all wrong.

If “the business” is changing the workflows without developer involvement, invariably something breaks, and then they don’t know what to do. They haven’t been trained to think the way that developers have – they don’t really know how to debug. So the developers are brought back in anyway and from that point on, the business is once again giving requirements and the devs are the one implementing it.

Now when it comes to developer productivity, I can tell you that the keyboard is at least 10x more productive than the mouse. I can bang out an if statement in code much faster than draggy-dropping a diamond on the canvas, and two other activities for each side of the clause.

On maintainability

Sometimes the visualization of the workflow is presented as being much more maintainable than “regular code”.

When these workflows get to be to big/nested/reused, it ends up looking like the wiring diagram of an Intel chip (or worse). Check out the following diagram taken from the DailyWTF on a customer friendly system:


The bigger these get, the less maintainable they are.

Now, some would push back on this saying that a method with 10,000 lines of code in it may be just as bad, if not worse. The thing is that these workflow tools guide developers down a path where it is very likely to end up with big, monolithic, procedural, nested code. When working in real code, we know we need to take responsibility for the cleanliness of our code using object-orientation, patterns, etc and refactoring things when they get too messy.

Here is where I’d bring up the SOA/pub-sub approach as an alternative – there is no longer this idea of a centralized anything. You have small pieces of code, each encapsulating a single business responsibility, working in concert with each other – reacting to each others events.

Productivity take 2: testing and version control

If you’re going to take your most complex and volatile business logic and put it into these workflow tools, have you thought about how your going to test it? How do you know that it works correctly? It tends to be VERY difficult to unit-test these kinds of workflows.

When a developer is implementing a change request, how do they know what other workflows might have been broken? Do they have to manually go through each and every scenario in the system to find out? How’s that for productivity?

Assuming something did break and the developer wants to see a diff – what’s different in the new workflow from the old one, what would that look like? When working with a team, the ability to diff and merge code is at the base of the overall team productivity.

What would happen to your team if you couldn’t diff or merge code anymore?
In this day and age, it should be considered irresponsible to develop without these version control basics.

In closing

There are some cases where these tools might make sense, but those tend to be much more rare than you’d expect (and there are usually better alternatives anyway). Regardless, the architectural analysis should start without the assumption of centralized workflow, database, or centralized anything for that matter.

If someone tries to push one of these tools/architectures on you, don’t walk away – run!

Integration: How and Where

Friday, April 8th, 2011

integrationOne of the topics that comes up a lot in the context of an Enterprise Service Bus (ESB) is that of integration. Unfortunately, many people take their ideas of reuse and design their integration as being done from a single place – both logical and physical. That unfortunately creates a bottleneck for all integration activities, where some are likely to be higher priority than others.

The ugly truth

You don’t need an ESB for integration.

There. I’ve said it.

Most of the ESB products on the market, in focusing on integration, are addressing the wrong problem.

What integration is about

There are three primary components to integration – data format translation, protocol bridging, and logic. Let’s take the Agile “simplest solution that could possibly work” motto and apply it to these elements:

  1. Data format translation
    • Use something like MapForce (from Altova, the guys behind XMLSpy).
    • At under $1200 for a dev license and handling mapping to/from XML, EDI, flat files, and relational databases, you can host the resulting mapping in any endpoint, as XSLT or even Java/C# – no need to have “the bus” do this for you.
  2. Protocol bridging
    • Use something like /n software
    • At about $1500 for a dev license, you get solutions for FTP, HTTP, SMTP, POP, IMAP, LDAP, DNS, RSS, SMS, Jabber, SOAP, WebDav, etc and, again – you can host the DLLs in any endpoint you want. Don’t need expensive buses for this
  3. Logic
    This is all you – no technology can do this for you. If anything, the most important thing is to get all the ugly mapping and protocol bridging stuff out of the way and let you focus on your logic. This is Single Responsibility Principle (un)common sense.

Digging deeper into the logic

The interesting thing about most of the protocol stuff mentioned above is that they’re inherently unreliable and also their performance at runtime is unknowable due to the total load on the target server.

We wouldn’t want any of the above situations to cause our integration to “get stuck”. As such, it is best we think of our integration logic as a long-running process that manages other endpoints which do the actual protocol bridging and data transformations.

This is one of the areas where NServiceBus, with its sagas can actually help a lot. Just like the other pieces of integration mentioned above, these sagas can run on any endpoint.

You could alternatively look at other technologies like BizTalk and Business Process Execution Language (BPEL) engines, though many of those are designed to be physically centralized (just like many of the ESBs out there).

By the way, if you do want to use NServiceBus together with BizTalk, Michael Stephenson has published some great white papers on getting the two to work together. His latest is about integrating NServiceBus into BizTalk’s RFID processes – check it out.

Putting it all together

When we take all of these pieces and look at them in a cohesive architecture, here’s what it can look like:

Distributed Integration

As you can see, integration is physically distributed across multiple endpoints.

Not only that, but the integration logic is kept separate from the protocol bridging and data transformation, enabling independent versioning of each. Just as important, it makes it much easier to unit test that the integration logic is correct as we don’t have to simulate the target technologies.


As you can see, you can get integration capabilities just as powerful as if you went with something like BizTalk, but without creating a single point of failure in your architecture. In terms of costs, it’s also quite a bit cheaper.

For a high availability BizTalk deployment, you’ll be paying over $40,000 per CPU for the Enterprise Edition, not including the extra $7000 per CPU for SQL Server Standard Edition (clustered). For a clustered 4-CPU mid-size deployment, you’d be in the area of $200,000.

For the distributed integration solution above, you’d be paying around $2700 in dev licenses (for /n software and Altova MapForce), and $500 per core for NServiceBus Standard Edition. The reason there’s per-core licensing for NServiceBus is that in a virtualized environment, you’ll be provisioning virtual cores to your virtual machines. No reason to pay for a quad-core CPU when all you’re using is a single core. You can also use any number of cores running NServiceBus Express Edition at no cost, so a mid-size deployment with say 8 cores running Standard Edition, and another 24 cores running Express Edition would cost (with the volume discount) an additional $3800 – a total cost of $6,500.

BizTalk: $200,000       NServiceBus: $6,500

‘Nuff said.

In closing

We’ve been bitten by centralized architectures before.

By having our integration distributed, we can version, upgrade, and scale each piece independently.

You’ve seen how we can use simple, lightweight, and inexpensive technologies to create distributed integration solutions just as powerful and robust as the centralized ESB vendor-offerings out there, but at a tiny fraction of the cost.

Next time the topic of integration is brought up, you’ll know not to be suckered in by re-branded EAI brokers.

Learn more about NServiceBus.

Bus and Broker Pub/Sub Differences

Thursday, March 24th, 2011

differencesOne of the things which often confuses people using NServiceBus for the first time is that it only allows an endpoint to subscribe to a given event from a single other publishing endpoint. The rule that there can only be a single publisher for a given event type is one of the things that differentiates buses from brokers, though both obviously allow you to have multiple subscribers.


Message brokers, more broadly known and used on the Java platform, don’t come with this constraint. For example, when using ActiveMQ, you can have any number of endpoints come to the broker and publish a message under a given topic.

So where’s the problem?

It’s all about accountability.

Let’s say you’ve subscribed to a given topic, and have received two events – one telling you that the price of bananas next week will be $1/kg and another telling you that it’ll be $2/kg.

Which one is right?

Especially given that those events may have been published by any other endpoint via the broker.

Is it first one wins? Last one wins? How about first one sent vs. first one received? Ditto for last. As a subscriber, can you really be held accountable for having the logic to choose the right one? Shouldn’t this responsibility have fallen to the publishing side?

This is one of the big drawbacks of the broker, hub and spoke architecture. No responsibility. No single source of truth – unless everybody’s going to some central database, in which case – what’s the point of all this messaging anyway?


The Bus Architectural Style is all about accountability. If you are going to publish an event, you are accountable for the correctness of the data in that event – there is no central database that a subscriber can go to “just in case”. And the only way that you can be held accountable, is if you have full responsibility – ergo, you’re the only one who can publish that type of event.

If you say bananas are going to cost $1/kg next week, that’s that. Subscribers will not hear from anybody else on that topic.

Now, this is not to say that you can’t have more than one physical publishing endpoint.

You see, buses differentiate between the logical and the physical. Brokers tend to assume that the physical hub-and-spoke topology is also the logical.

In a bus, while there can only be one logical endpoint publishing a given type of event, that endpoint can be physically scaled out across multiple machines. It is the responsibility of the bus to provide infrastructure facilities to allow for that to happen in such a way that to subscribers, it still appears as if there is really only one publishing endpoint.

The same is true about the subscriber – one logical subscribing endpoint may be scaled out across multiple machines.

Product Mix-ups

Unfortunately, there are many broker-style technologies out there that are being marketed under the banner of the Enterprise Service Bus. While some products have the ability to be deployed in both a centralized and distributed fashion (sometimes called “federated” or “embedded” mode), many do not enforce the “single publishing logical-endpoint per event-type” rule.

Without this constraint, it is just too easy to make mistakes.


By enforcing this constraint, we see the same kind of question appear on the discussion group time and time again:

“I have an Audit event that I’d like all of my machines to publish, and have one machine subscribe to them all, but NServiceBus won’t let me. How do I make NServiceBus support this scenario?”

And the answer is the same every time:

“You should have all the machines Send the Audit message (configured to go to the single machine handling that message), and not Publish. It is not an event until its been handled by the endpoint responsible for it.”

The semantics of the message matter a lot.

When looking at Service-Oriented Architecture, these messages are the contract and, as any lawyer will tell you, contracts need to be explicit and the intentions really need to be spelled out – otherwise the contract is practically worthless.

In closing

Friction is sometimes a good thing – it prevents us from making mistakes. It keeps cars on the road. And because that’s not enough friction, we introduce curbs as well.

If you’re looking for a service bus technology for your next project, check that it’ll give you the friction that you need to keep everybody safe. Really check what it is that the vendors are offering you – more often than not, it’s some ESB lipstick on a broker pig.

To learn more about how NServiceBus supports this kind of publish/subscribe, click here.

Polymorphism and Messaging

Thursday, January 13th, 2011

polymorphismOne of the questions that came up from my NServiceBus – .NET Service Bus Smackdown post was about the Polymorphic Message Dispatch and Polymorphic Message Routing features. People wanted to know what those are, why they’re important, and if other technologies (specifically WCF and BizTalk) support them.

Messaging Basics

First of all, when building a system using messaging, you don’t have methods that are invoked on some remote object (a.k.a “service”) to which you pass parameters. Instead, you use some generic piece of infrastructure (in the world of Java, this is most commonly a Message Broker) to send a message where a message can be thought of as a serializable class. Here’s an example of a message:

public class UserCreated : IMessage
    public Guid UserId { get; set; }
    public string Name { get; set; }

This message would be published using NServiceBus like this:

bus.Publish<UserCreated>( m =>
    m.UserId = Guid.NewGuid();
    m.Name = "John Smith";

This can be contrasted with RPC models like WCF where you need to define a “service” that has methods on it, where those methods accepts parameters. Sometimes developers try to make this more generic by having a single “service” with one method on it named something like “Process” where the parameter it accepts is of the type “object”, or they introduce generics like this: Process<T>(T message);

This is where Polymorphic Message Dispatch comes in:

Polymorphic Message Dispatch

While you can pull of the WCF generics thing, one thing that is more difficult (without writing your own dispatch model) is to have a pipeline of classes which can be invoked based on their relationship to the type passed in. Using NServiceBus, both of the following message handlers will be invoked when UserCreated arrives:

public class Persistence : IHandleMessages<UserCreated>
    public void Handle(UserCreated message) { }

public class Audit : IHandleMessages<IMessage>
    public void Handle(IMessage message) { }

Now some might say that WCF, BizTalk, and the .NET Service Bus allow you to do auditing in their own internal pipeline, and that’s true. The place where this becomes more powerful is when you need to build V2 of your system, and the publisher now publishes a slightly different event – that a user was created as a part of a campaign, requiring the subscriber to register statistics about the campaign. Of course, this event also means that a user was created. Here’s how you’d do that with NServiceBus:

public class UserCreatedFromCampaign : UserCreated
    public Guid CampaignId { get; set; }

//publisher code
bus.Publish<UserCreatedFromCampaign>( m =>
    m.UserId = Guid.NewGuid();
    m.Name = "John Smith";
    m.CampaignId = theCampaignId;

//subscriber code
public class Statistics : IHandleMessages<UserCreatedFromCampaign>
    public void Handle(UserCreatedFromCampaign message) { }

The important part is what you don’t see – since UserCreatedFromCampaign inherits from UserCrated, the Persistence handler we had from V1 will also be invoked, and so will the Audit handler of course. You don’t have to make your new code call the old code like you would in a method based dispatch model. This makes sure that the coupling in your service layer code remains constant over time as you grow the functionality of your system.

This was one of the main benefits mentioned by Rackspace in their use of NServiceBus (here):

“The main benefit NServiceBus has brought us so far is developer scalability due to lower coupling and higher consistency in our code.”

But, when looking at the above scenario, we can obviously expect that all sorts of things can happen in relation to campaigns – it is a separate concern, and thus should be handled by a separate subscriber. And this bring us to…

Polymorphic Message Routing

The challenge that we have here is that we no longer have a hierarchy where something clearly belongs on top of something else. We have users created and activities happening related to campaigns – that may happen in any combination. By having separate subscribers, we could then introduce new handlers/subscribers to our environment without touching or taking down any of the other subscribers. Here’s what the subscribers would look like:

public class Persistence : IHandleMessages<UserCreated>
    public void Handle(UserCreated message) { }

public class Statistics : IHandleMessages<CampaignActivityOccurred>
    public void Handle(CampaignActivityOccurred message) { }

But if each of the above messages were a class, how could we define a message which inherited from both?

Before answering that, we need to understand why the publisher wouldn’t just publish both of the above messages. You see, the publisher can’t make any assumptions about its subscribers – it could be that one of them has logic that correlates across both of these messages that could end up counting the occurrence as happening twice rather than once, possibly charging the account associated with the campaign twice. Publishing two messages results in two transactions when there really should have been one.

So, here’s how to define messages so that we can have multiple inheritance:

public interface UserCreated : IMessage
    Guid UserId { get; set; }
    string Name { get; set; }

public interface CampaignActivityOccurred : IMessage
    Guid CampaignId { get; set; }
    Guid ActivityId { get; set; }

public interface UserCreatedFromCampaign 
                 : UserCreated,

And when the publisher publishes UserCreatedFromCampaign, the event would be routed to both the UserCreated subscriber and the CampaignActivityOccurred subscriber. The power of this approach is felt as we handle new requirements around purchases made related to a campaign. Now we can have another event which inherits from CampaignActivityOccurred and not have to worry since the existing subscriber will be routed those messages automatically.

Since WCF doesn’t have publish/subscribe capabilities, we might as well move along.

Not to throw a burning match on an ocean of oil, but REST doesn’t really support this either.

Not Content-Based Routing

This may sound like the content-based router pattern from EIP (CBR), but it’s not. The important difference is that there isn’t some part of the routing that depends on the structure of the messages. The major drawback of CBR is that it creates a central place in your system that needs to be changed any time *syntactic* changes happen to message structure *in addition to* to changes in the subscribers.

Now, this is where the BizTalk guys would say that “that’s why we can do message transformations”, and then the subscribers wouldn’t need to be changed. However, can we really know when getting a requirement that the change is syntactic and not semantic? I mean, it’s quite common that changes to message structures happen together with changes to processing logic.

You may be beginning to get the feeling that more and more logic is being sucked out of the subscribers into some monolithic black hole that is likely going to be unmaintainable and quite slow.

This is one of the main differences between using a bus and a broker – a bus supports the correct distribution of logic keeping the system loosely coupled; brokers are useful integration engines when you absolutely can’t change the applications being integrated. Enterprise Application Integration (EAI) brokers don’t usually make good Enterprise Service Bus (ESB) technology.

In Closing

NServiceBus has all sorts of features you didn’t know you needed until you saw what life could be like when you had them. Most of these features don’t have snazzy drag-and-drop demos that make people ooh-and-aah and TechEds and PDCs, but they’re really necessary to avoid finding yourself in yet another big-ball-of-mud code base telling your manager/customer (again) that it would be faster to rebuild the system from scratch than to implement that new requirement in the old one.

Take NServiceBus for a spin and see for yourself.

Logical and Physical Architecture

Monday, November 8th, 2010

orthogonalOne architectural misunderstanding I see repeatedly in my work with clients is in the relationship between logical and physical architecture. The most common building-block of these misunderstandings is the web service (or it’s “upgraded” .net counterpart – the WCF service).

Don’t get me wrong, sometimes there is a place for a web service, just not everywhere.

So, what’s the problem?

Well, when developers and architects use web services as the building blocks of their designs, they are creating the same architecture for both the logical and physical elements of their system. Back in 1995, Philippe Kruchten documented his 4 + 1 Architectural View Model in which he outlined 4 + 1 different views that should be used to describe an architecture.

Even though since 1995 the number and types of recommended views of software architecture has evolved (with things like the Zachman Framework for enterprise architecture numbering some 30 views), there is broad agreement that (at the very least) the logical and physical artifacts should likely be designed differently.

Just because two distinct logical components have been identified in the architecture, that doesn’t necessarily mean they should be hosted separately (for example by making each one a web/wcf service). In fact, there are significant disadvantages to doing so (as described in the Fallacies of Distributed Computing).

In some cases, this mistake is exacerbated by a mistaking these components with SOA-type services, resulting in an attempt by developers to have each component have its own contract, which can then be independently versioned. This often results in the need for transformation between the structure of these so-called contracts, but not within the components themselves (oh-no, they’re “autonomous”), but rather in between them using some kind of “ESB” technology.

This architectural style is known as the Broker, Hub and Spoke, Mediator, and most importantly – not SOA. If you find a technology that fits this style perfectly (like BizTalk), that technology is not a Bus, not a Service Bus, and definitely not an Enterprise Service Bus.

One of the problems of this approach is that when any “service” contract changes, you have to change all the transformations in your broker that involve it. Unfortunately, most brokers have no unit-testing facility so it’s very much trial and error, and error, and error. The matter is even more serious since most brokers don’t enable you to have your transformations or orchestrations in source control, so you can’t diff to see what changed from the previous version.

It’s really amazing how much pain can be traced back to that one original misunderstanding.

BizTalk Blogs and UdiDahan.com, strange bedfellows?

Wednesday, December 19th, 2007

So, it turns out that Microsoft has quietly launched a new community-style site.

Titled "BizTalk Blogs", I wasn’t quite sure what my blog was doing there. It’s not that I never write about BizTalk – every once in a while I even find something nice to say about it 🙂 My quick post on BizTalk and Performance is one such example. But, let’s face it, a lot of the work I do is to provide BizTalk-like features like routing, transaction-management, and choreography (orchestration) without the actual product.

Apparently, I’m not the only non-BizTalk-only blogger there.

Including such names as Christian Weyer and Michelle Leroux Bustamante , there is a veritable who’s who in the Microsoft Connected Systems ecosystem and, quite frankly, I’m surprised the bouncer let me in the door.

So, this post is for my readers who, like me, have pretty much ignored anything looking like BizTalk for the past few years. Don’t let the name fool you. BizTalk Blogs is a valuable resource even for people who don’t care about BizTalk – and hey, you might even like what you start hearing about the future directions Microsoft is taking it.

But that’s enough of that. We’ll be back with your regularly scheduled BizTalk bashing right after this break…

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.

No such thing as a centralized ESB

Saturday, June 30th, 2007

Via David McGhee’s Q&A with Dr. Don Ferguson, but read the whole thing.

Q: Could you tell you your thoughts or preference for a distributed or centralized ESB?

DON: there is no such thing as a centralized ESB.

This is the problem with a lot of the products that call themselves ESBs. They are centralized brokers which may be clustered for availability. But they are in no way an implementation of the Bus Architectural Pattern. Please check this before cutting a check to your vendor.

Also, understand that if you do security related things in your ESB, possibly as a part of your routing rules, that if the security infrastructure is centralized that means your ESB is too. Even if it really was distributed to begin with.

Buyer beware.

BizTalk and Performance

Wednesday, May 2nd, 2007

I know I bad-talk BizTalk a lot, but I do it somewhat tongue-in-cheek and to get a rise out of people. BizTalk is a tool, something of a swiss army knife, you know, those huge, honking ones that have everything but the kitchen sink in them. One of the main areas where BizTalk gets a bad rap is in performance and scalability. On the other hand, the number of systems that I come in to assist with performance issues, that don’t use BizTalk, is still quite large. A systematic approach is needed in all cases.

I ran into another BizTalk optimization story online that once again points out that disk IO is a good first place to look, as I wrote about in my Database performance optimization article.

In closing, you need to be aware of the full environment. For instance, in BizTalk, it’s not just about messages per second. Session contention (multiple parties hitting the same session) can just lock things up tighter than, well, a tight thing. Designing for these things “up front” can save you very costly rewrites later.

Request/Service state affinity – don’t.

Sunday, February 18th, 2007

I saw this question today on the one of the blogs I follow, and seeing that it’s a question that variations of it pop up all the time, I thought that I’d chip in with my 2 cents.

How do I store some state about the current request so that I can use it later during the same service operation?

One analysis I read came at it from a technological angle – how to do this with WCF. I want to take a look at two other angles here.

The first has to do with one interpretation of the question – in the course of handling that request, there are numerous objects involved. How can we make it so that all of them have access to the request data? From a technological perspective, the answer is simple – make it thread-static (in .net this is done by applying the ThreadStaticAttribute to it), or store it in some thread-local-storage. From a design perspective, though, things aren’t all that clear. Which property of which class contains the request data, so that we can mark it with such an attribute, or under what key is the data stored in the thread-local-storage?

What I usually do is use my “IBus” interface, which exposes a “MessageBeingHandled” thread-static property. Any object that needs state about the current request makes sure to get an instance of “IBus” injected. The classic example of objects that need this data include message handlers (implementing the “IMessageHandler” interface). For more information about this design, take a look at this.

The second interpretation looks at having that request data available to the service on subsequent invocations. Personally, I don’t like the idea of having this data in-memory on the object that serviced the original request. One reason I don’t like it is that it creates an affinity between the client and the specific server handling its requests. Those of you who know me already are expecting this…

What if the server restarts?

Will that client’s state be lost? Well, not if we persisted it somewhere durable instead of just in memory. Will we stop servicing requests from that client until the original server becomes available again? Well, if the data was durably persisted, then any server could pick it up. And this is exactly what BizTalk does. You don’t want to implement BizTalk again, do you?

I can tell that some of you are surprised to hear me say this. Such a small requirement, and already we need BizTalk? Did Udi really say that?

Well, there is another, simpler way. If what you have is some kind of back-and-forth between the client and the service, you could use the Message History pattern and pack up the previous request data into the messages being sent. Although we’re increasing the message size, we’ve made it so that any server can handle any request and have access to all the previous data without creating some sort of durable contention area within the service like a database. Another option is to look at long-running workflow to model these interactions.

Finally, when it comes to ultra-scalable systems, I strongly suggest keeping the network dumb and pushing the smarts out to the edges – the clients. If you don’t need to have one client pick up where another client left off, this could be the ultimate solution. It combines with the Message History pattern and ends up sending only the data necessary on subsequent requests, thus keeping message size to a minimum. Also, your service doesn’t have to handle the state any more making it capable of handling more concurrent clients.

State management is the heart of any distributed systems development effort. Unfortunately, there aren’t any easy answers to it, but it’s important not to gloss over it if you want to have any hope of scalability in the future. Patterns help, but eventually we have to make the tradeoffs ourselves. Just don’t go running to one product or another in the hopes that it will make everything magically better.


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Bryan Wheeler, Director Platform Development at msnbc.com
Udi Dahan is the real deal.

We brought him on site to give our development staff the 5-day “Advanced Distributed System Design” training. The course profoundly changed our understanding and approach to SOA and distributed systems.

Consider some of the evidence: 1. Months later, developers still make allusions to concepts learned in the course nearly every day 2. One of our developers went home and made her husband (a developer at another company) sign up for the course at a subsequent date/venue 3. Based on what we learned, we’ve made constant improvements to our architecture that have helped us to adapt to our ever changing business domain at scale and speed If you have the opportunity to receive the training, you will make a substantial paradigm shift.

If I were to do the whole thing over again, I’d start the week by playing the clip from the Matrix where Morpheus offers Neo the choice between the red and blue pills. Once you make the intellectual leap, you’ll never look at distributed systems the same way.

Beyond the training, we were able to spend some time with Udi discussing issues unique to our business domain. Because Udi is a rare combination of a big picture thinker and a low level doer, he can quickly hone in on various issues and quickly make good (if not startling) recommendations to help solve tough technical issues.” November 11, 2010

Sam Gentile Sam Gentile, Independent WCF & SOA Expert
“Udi, one of the great minds in this area.
A man I respect immensely.”

Ian Robinson Ian Robinson, Principal Consultant at ThoughtWorks
"Your blog and articles have been enormously useful in shaping, testing and refining my own approach to delivering on SOA initiatives over the last few years. Over and against a certain 3-layer-application-architecture-blown-out-to- distributed-proportions school of SOA, your writing, steers a far more valuable course."

Shy Cohen Shy Cohen, Senior Program Manager at Microsoft
“Udi is a world renowned software architect and speaker. I met Udi at a conference that we were both speaking at, and immediately recognized his keen insight and razor-sharp intellect. Our shared passion for SOA and the advancement of its practice launched a discussion that lasted into the small hours of the night.
It was evident through that discussion that Udi is one of the most knowledgeable people in the SOA space. It was also clear why – Udi does not settle for mediocrity, and seeks to fully understand (or define) the logic and principles behind things.
Humble yet uncompromising, Udi is a pleasure to interact with.”

Glenn Block Glenn Block, Senior Program Manager - WCF at Microsoft
“I have known Udi for many years having attended his workshops and having several personal interactions including working with him when we were building our Composite Application Guidance in patterns & practices. What impresses me about Udi is his deep insight into how to address business problems through sound architecture. Backed by many years of building mission critical real world distributed systems it is no wonder that Udi is the best at what he does. When customers have deep issues with their system design, I point them Udi's way.”

Karl Wannenmacher Karl Wannenmacher, Senior Lead Expert at Frequentis AG
“I have been following Udi’s blog and podcasts since 2007. I’m convinced that he is one of the most knowledgeable and experienced people in the field of SOA, EDA and large scale systems.
Udi helped Frequentis to design a major subsystem of a large mission critical system with a nationwide deployment based on NServiceBus. It was impressive to see how he took the initial architecture and turned it upside down leading to a very flexible and scalable yet simple system without knowing the details of the business domain. I highly recommend consulting with Udi when it comes to large scale mission critical systems in any domain.”

Simon Segal Simon Segal, Independent Consultant
“Udi is one of the outstanding software development minds in the world today, his vast insights into Service Oriented Architectures and Smart Clients in particular are indeed a rare commodity. Udi is also an exceptional teacher and can help lead teams to fall into the pit of success. I would recommend Udi to anyone considering some Architecural guidance and support in their next project.”

Ohad Israeli Ohad Israeli, Chief Architect at Hewlett-Packard, Indigo Division
“When you need a man to do the job Udi is your man! No matter if you are facing near deadline deadlock or at the early stages of your development, if you have a problem Udi is the one who will probably be able to solve it, with his large experience at the industry and his widely horizons of thinking , he is always full of just in place great architectural ideas.
I am honored to have Udi as a colleague and a friend (plus having his cell phone on my speed dial).”

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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