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Archive for the ‘Messaging’ Category



People, Politics, and the Single Responsibility Principle

Monday, May 26th, 2014

PeopleIn one of Uncle Bob’s recent blog posts on the Single Responsibility Principle he uses the example of using people and organization boundaries as an indication of possible good software boundaries:

When you write a software module, you want to make sure that when changes are requested, those changes can only originate from a single person, or rather, a single tightly coupled group of people representing a single narrowly defined business function. You want to isolate your modules from the complexities of the organization as a whole, and design your systems such that each module is responsible (responds to) the needs of just that one business function.

This is something that often comes up when I teach people about service boundaries when it comes to SOA – organization boundaries are the most intuitive choice.

And, once up on a time, that intuition might have indeed held up.

Stepping back in time

In the age before computers, organizations had a very specific way of structuring themselves.

People who had to work closely together sat in close physical proximity to each other. Data that was required on an ongoing basis would be in file cabinets also physically co-located with the people using that data, and it would be structured in a way that was optimal for their specific purposes. All of this was due to the high cost of communicating with people farther away.

If you needed data from a different department, you had requisition it by filling out a special form, put it in your outbox, and then some guy from the mail room would pick it up, and physically schlep it to the right department, putting it in their inbox, and then someone there would get your data for you – putting it together with your original request, and then the mail guy would schlep it back. This inbox/outbox style of communication should ring a bell from the messaging patterns I talk about with NServiceBus.

As a result, different departments had to have very clearly delineated responsibilities with minimal overlap with each other. The organization just couldn’t function any other way.

And then a bunch of us geeks came along.

Enter the age of computers and networks

By introducing this technology, the cost of communication across large distances started falling – slowly at first, and then quite dramatically.

When anyone in an organization was able access data from anywhere in the blink of an eye, an interesting dynamic started to unfold. All of a sudden, the division of responsibility between departments wasn’t as critical as it was before. When an employee needed to do something, there wasn’t this “that isn’t our job, you need to go to so-and-so” reaction. Because things could be done instantly, that’s exactly what happened.

And then came the politics

By removing the cost of communication, it became possible for more power-hungry people in the organization to start making (or trying to make) decisions that they couldn’t have made before. The introduction of computers into an organization was heralded as a new way of doing business – that the old organizational boundaries were a relic that we should leave behind us.

And thus can the re-org (the first of many).

Responsibilities and people were shuffled around, managers vied for more power, and politics took its’ place as one of the driving forces in the company structure.

Nowadays, if you want a decision made in a company, there isn’t just one person who has the authority to sign off on it anymore. No, you need to have meetings – and more meetings, with people you never knew existed in the company, or why on earth they should have a say on how something is supposed to get done. But that is now our reality: endlessly partially overlapping responsibilities across the organization.

So, what of the Single Responsibility Principle

This just makes it that much harder to decide how to structure our software – there is no map with nice clean borders. We need to be able to see past the organizational dysfunction around us, possibly looking for how the company might have worked 100 years ago if everything was done by paper. While this might be possible in domains that have been around that long (like banking, shipping, etc) but even there, given the networked world we now live in, things that used to be done entirely within a single company are now spread across many different entities taking part in transnational value networks.

In short – it’s freakin’ hard.

But it’s still important.

Just don’t buy too deeply into the idea that by getting the responsibilities of your software right, that you will somehow reduce the impact that all of that business dysfunction has on you as a software developer. Part of the maturation process for a company is cleaning up its’ business processes in parallel to cleaning up its’ software processes.

The good news is that you’ll always have a job :-)



NSBcon London 2014

Tuesday, April 22nd, 2014

NSBconSince my last post announcing NSBcon you probably haven’t gone to take a look at what’s happening.

The speaker lineup for NSBcon London 2014 is now complete and we’ve got a really great mix of talks, if I do say so myself.

I’ve already mentioned that Oren and Greg will be there, but I wanted to talk a bit about the rest of the roster:

First up – Wonga

If you’re living in the UK, you almost can’t avoid seeing these ads.

Wonga

What you probably didn’t know is that Wonga has been running on NServiceBus for years now.
(No – we had nothing to do with the ads, and there’s nothing we can do about them.)

Charlie Barker was there from the beginning and has lived to tell the tale:

We faced the problem of scaling our platform to meet rapid growth in customers whilst at the same time increasing the team from 15 to 200 people spread across five countries. We did this by transitioning from N-Tier to SOA even as we were delivering new features and keeping the platform stable. No small feat.

This is an interesting story to hear, not only from the point of view of NServiceBus, and I’d definitely recommend grabbing Charlie over lunch or over a beer. This is probably one of the higher profile startup successes in the UK you’ll find and, as always, the behind the scenes story is just fascinating.

And to the cloud!

No self-respecting technology conference these days can go without spending at least some time talking about the cloud – and we won’t be the ones to buck the trend, even though we have a healthy disrespect for all sorts of things, including the ourselves :-)

You’ll hear from one of the foremost Azure MVPs and all around cloudy Belgian Yves Goeleven (whose last name nobody is really sure how to pronounce). Yves has been the driving force behind getting all the various bits of Azure infrastructure integrated into NServiceBus and, if you get him to just the right level of inebriation, will spill all the dirty little secrets of the Azure platform that Microsoft doesn’t want anyone to know.

Dylan Beattie will then relate his tales of creating loosely-coupled encoding workflows for audio and video on the cloud at Spotlight – one of the world’s leading resources for professional actors, casting directors, and production professionals. It ain’t easy making ordinary people into stars.

And so much more

To see the complete lineup, go to NSBcon.com.

And me – what will I be talking about? That’s a good question.

Not to steal my own thunder (after stealing everybody else’s), but you’ll hear about the deeper integration we’ve got planned for SignalR, making your event-driven architecture extend from the back of your systems all the way to the browser, so much simpler and smoother than you ever thought possible.

I’ll also tell you about how we’re going to enable you to run on queues that don’t support distributed transactions (like Service Bus for Windows Server) without having to worry about making your logic idempotent. For some background, see my blog post on Life without distributed transactions.

In short – it’s going to be a kick-ass conference.

Check it out.

* and for those of you paying out of pocket, contact nsbcon@particular.net for a discount.



Announcing the Particular Service Platform

Wednesday, April 16th, 2014

champaignAfter many months of hinting about the coming of the Particular Service Platform, it’s finally here.

For everybody who has been building message-driven systems on .NET – I really do believe that this is the dawn of a new era (and if you know anything at all about me, you know that I don’t tend to exaggerate).

What is it?

Imagine designing your solution by graphically creating endpoints and messages, seeing the routing laid out in front of you visually, being able to specify system wide error and audit queues, having your cross-cutting authentication applied automatically to all endpoints, correlating events together into sagas, pressing F5, and as everything springs to life, on your second monitor you can see the messages flowing through your specific debug session synchronized in real time as you step through your code.

Well, you don’t have to imagine – that’s now a reality.

Top that off with some nice production monitoring that includes heartbeats for all of your endpoints, notification of message processing failures (with the ability to send them back for reprocessing), and some cool extensibility to plug in your own custom checks.

It’s a whole new world of service-oriented development.

This short video will give you a sense of what it’s like:


Here’s some other things you might find interesting.

Testing you can trust

I’ll bet you didn’t know the level of testing that we’re now putting into each release.

Every time we put out a new release, we test it on cloud servers configured across all permutations of transports, containers, persistence technologies, server operating systems, as well as for compatibility with previously released versions 2 years back (!). This way, when you want to have a new system subscribe to events published by a system already in production, you’ll know that it will all “just work” – no matter what.

Running all of these tests in the cloud is something that we could never afford back when we were a regular free/open-source project, but is definitely worth it. We know you count on us for your mission-critical systems and will continue doing our very best to be worthy of that trust.

The roadmap

Now that the platform is out, the next big thing you can expect is the removal of all distributed transactions.

Over the past months (and even years) we’ve been making preparations for this, making all sorts of small backwards compatible changes and enhancements so that we can fully control the inbound and outbound behavior of messages. The investments we’ve been making in automated tests is also in support of this. We want to be absolutely positive that you will get the exact same logical behavior as before without losing any of the transactional guarantees you’ve come to expect from NServiceBus.

We’ll give you updates on this and the other things we’re working on soon, as part of our larger roadmap so that you’ll know roughly what kind of big features you can expect and when. Of course, we always leave some “slack” in our iterations for working on critical patches, enhancements, and refactoring.

In any case, the main idea here is for you to be able to give us feedback and input on what’s important to you and for us to communicate back what we will be able to commit to and when.

Expressing our thanks

It’s been quite a journey this past year – the company has doubled in size and we’ve really got a great group of people here. While we’re constantly looking ahead and seeing all the wonderful things that we want to do, I wanted to take a moment and look back.

It’s been almost two years of work on ServiceMatrix (previously named NSB Studio) – the absolute biggest investment we’ve made. This past year was really the biggest push, and when taken together with all of the other tools – the production monitoring in ServicePulse that so many people have been clamoring for; the under-the-hood visibility of ServiceInsight; and the unseen glue of ServiceControl tying them all together; well, it was a very ambitious year.

I wanted to thank everyone who took part in our betas – your feedback was absolutely invaluable;

To our Community Champs who keep asking us the difficult questions and pushing us to do better;

To all of you in our community who have believed in us;

To the growing ranks of paying customers who voted with their wallets as well as their hearts;

You have my personal thanks as well as those of the entire team.
It continues to be an honor and a privilege.

Go and get it

That’s it – go to www.particular.net and click the big “download now” button and take the new platform for a spin!

I can’t wait to hear what you all think.



Loosely-coupled orchestration recording now online

Monday, April 7th, 2014

When I was in London a couple of weeks ago teaching my SOA class, I gave an evening presentation called Loosely-Coupled Orchestration which talked about some of the challenges people face when introducing more event-driven and asynchronous patterns into their systems – for example, dealing with out-of-order message delivery.

I’m happy to say that the recording of that session is now online, courtesy of the good folks at Skills Matter, and you can now view that here.

In this presentation, you’ll also see a lot of the new capabilities that will be coming out soon with the release of our new Particular Service Platform – the suite of tools that makes NServiceBus that much more awesome. From monitoring of production issues, to debugging cross-endpoint message flows, to modeling of message-driven & service-oriented systems, it really takes distributed systems development to the next level.

Check it out!

Oh, I almost forgot, there are still some seats left for my course in New York City. Details here.



Code for my Programming in 4D talk

Wednesday, April 2nd, 2014

Click here for the animationSo, I’ve been a bad presenter.

I’ve given my Programming in 4D talk already several times and I haven’t yet uploaded the code for it.

And seeing as I’m going to be giving it again today (at the DevWeek conference in London), I figured that I should finally get my act together and put it online.

Interestingly enough, the other conferences I’ve spoken at either didn’t record it or didn’t put the recording online. Hopefully DevWeek will do better <FingersCrossed/>.

The overall solution

The scenario I talk about in this presentation is (again) a standard one in the world of retail: customers who want to return products that they’ve purchased and get a refund.

I’ve used our new ServiceMatrix tooling to model the solution like this (click for a larger image):

RefundPolicySolution

If you’d like to download the complete solution, click here.

Now, we’re going to focus on the RefundPolicy object that you can see towards the bottom left.

The Refund Policy

So, in this scenario, what we’re going to implement is a process whereby if you return your products within 30 days of the purchase, you’ll receive a 100% refund; if you return your products within 60 days you’ll receive a 50% refund, and anything longer than that and no refund for you.

Here’s the code:

public class RefundPolicy : Saga<RefundPolicySagaData>, 
                            IAmStartedByMessages<OrderAccepted>, 
                            IHandleMessages<ProductsReturned>, 
                            IHandleTimeouts<Percent>, 
                            IHandleSagaNotFound
{
    public void Handle(OrderAccepted message)
    {
        Data.OrderId = message.OrderId;
        Console.WriteLine("OrderAccepted");
 
        Data.Percent = 100;
 
        RequestTimeout(TimeSpan.FromDays(30), 50.Percent());
        RequestTimeout(TimeSpan.FromDays(60), 0.Percent());
    }
 
    public void Handle(ProductsReturned message)
    {
        Console.WriteLine("ProductsReturned");
 
        Bus.Send<IssueRefund>(m => m.Percent = Data.Percent);
        MarkAsComplete();
    }
 
    public override void ConfigureHowToFindSaga()
    {
        ConfigureMapping<ProductsReturned>(m => m.OrderId).ToSaga(s => s.OrderId);
    }
        
    public void Timeout(Percent state)
    {
        Console.WriteLine("Timeout");
        Data.Percent = state;
 
        if (state == 0)
            MarkAsComplete();
    }
 
    public void Handle(object message)
    {
        if (message is ProductsReturned)
            Console.WriteLine("No refund for you");
    }
}
 
public class RefundPolicySagaData : ContainSagaData
{
    [Unique]
    public int OrderId { get; set; }
 
    public Percent Percent { get; set; }
}


And what’s so good about that?

Well, not to steal my own thunder and give you a reason not to watch the video when it comes out, the trick is in the two RequestTimeout calls that are invoked when an OrderAccepted message arrives. You see, what that does is that it takes the data that defines the behavior of the refund policy and persists that via a queue, which will play back the data to our object according to the defined schedule.

This way, if/when the business decides to change the rules (say, reducing the timeframes to 20 days and 40 days), that will only affect users who are placing new purchases. The customers who made a purchase 50 days earlier (when the rules were still 30/60) will get the correct behavior applied to them.

Next steps

Of course, nobody would want a developer to have to open this code and change it in order to make a simple change like 30/60 -> 20/40, so we could externalize the data by creating a dictionary property on the saga where the key is the TimeSpan and the value is the Percent. Then, we could pull those values from either a config file or database and inject them into the property on the saga.

Here’s how the code of the saga would change:

public class RefundPolicy : Saga<RefundPolicySagaData>, 
                            IAmStartedByMessages<OrderAccepted>, 
                            IHandleMessages<ProductsReturned>, 
                            IHandleTimeouts<Percent>, 
                            IHandleSagaNotFound
{
    public Dictionary<TimeSpan, Percent> DataDefinitions { get; set; }
 
    partial void HandleImplementation(OrderAccepted message)
    {
        Data.OrderId = message.OrderId;
        Console.WriteLine("OrderAccepted");
 
        Data.Percent = 100;
 
        foreach(var kv in DataDefinitions)
            RequestTimeout(kv.Key, kv.Value);
    }

And the code to do the property injection would look like this:

public class RefundPolicyDataConfigurator : INeedInitialization
{
    public void Init()
    {
        Dictionary<TimeSpan, Percent> data = null /* get from config instead */;
        Configure.Instance.Configurer
            .ConfigureProperty<RefundPolicy>(p => p.DataDefinitions, data);
    }
}

Classes the implement INeedInitialization are invoked at process startup, and that call to ConfigureProperty instructs the container to set the DataDefinitions property of our RefundPolicy every time it is resolved (which is on every message).

In closing

We now have a solution which allows non-developers to make changes to the refund policy definitions without requiring us to deploy any new code to production. Also, any changes that are made will preserve the promises we made to our users in the past.

Of course, if you want changes to rules to impact all users immediately, this approach wouldn’t be so good.

Again, if you’d like to download the complete solution, the code is here, and if it wasn’t already obvious, this code makes use of NServiceBus quite heavily.

When the recording comes online, I’ll update this post with a link as well as do another blog post.

Hope you like it.



Ask Udi 1: Alternative Architectures & Preaching to the Unconverted

Friday, June 28th, 2013

As promised, the podcast is back.

Download episode 1 here      and then      Subscribe to the feed.

There were 16 questions submitted and a couple hundred votes for the various topics. I was able to cover the top two questions.

Do you have a question you want to ask?
Want to vote on which questions will be answered next week?
Click here

This week’s questions

Rob Eisenberg asked:

It seems that every project I walk into has the exact same architecture, regardless of what the company is building. It’s that standard 3-tier pattern: data-business-presentation. But, there are other large-scale architectural patterns available. I’d love to hear some case studies that pair business problems with the rationale for choosing an “alternative architecture.”

And since it’s not just about knowing the right approach but also being able to convince others, I included Rvonwink’s question too:

Some of us see the genuine benefits of pub/sub, EDA and SOA design. However, how do you go about persuading the cynics, time pressed and uninformed:

Our developers hate debugging pub/sub models; Others love the ’simplicity’ of monolithic domains; Our DBA questions why messaging is required (since “the bus simply persists messages elsewhere”); Our sys admins hate deploying new applications or changing the deployment topology; Our boss is scared to tell the business there is a little extra work to start splitting apart services.

Next week

Currently the top questions for next week are:

  • Composite UI, Business Components and Deployment
  • How to handle predetermined technology choices
  • How do you manage NULL pointer exception in general?

What would you like to hear? Let me know.

Until next week…



Life without distributed transactions

Monday, December 31st, 2012

transactionsOccasionally I get questions about the issue of transactional messaging – why is it so important, why does NServiceBus default to this behavior, and if we didn’t use it, what bad things could happen. I’m talking specifically about the ability to enlist a queue in a distributed transaction here.

I think the reason for this interest is the rise in popularity of cloud platforms and queuing systems like RabbitMQ (which don’t support distributed transactions) and the difficulty of setting up distributed transactions even in on-premise.

Of course, there’s also the regular scalability hand-wringing going on even though most people wouldn’t bump up against those limits anyway.

In this post, I’ll talk about the nature of the problem, explain the pitfalls in some of the common solutions, but I’ll put off the description of how to provide consistency without distributed transactions to a future post as this one is already going to be quite long.

I’ll start with the basic fault-tolerance issues and then explain how things spiral out from there.

Starting with the basics

OK, so we have a queuing system in place that dispatches messages to our business logic which does some transactional work against a database.

Let’s say that we completed the transaction against our database but before we could acknowledge to the queue that the message was processed successfully, our machine crashed. What our machine comes up again, the queue will once again dispatch us the same message. Unless we have some logic to detect that we’ve already processed it (called “idempotence” in the REST community), we will end up processing it again.

In short, the problem is duplicates.

Attempted solutions to the duplicate problem

Most queuing systems don’t do anything about duplicates, actually giving it a proper architectural name: At-least-once message delivery, as opposed to the Once-and-only-once model that a queue that supports distributed transaction provides.

The solution often suggested is to have your logic check to see if it has already processed a message with that ID before – in essence storing the ID of each message processed for some period of time. Of course, there is some performance overhead with that, but it might be a small price to pay compared to dealing with it in the logic of every use case.

On the other hand, you’ll often have some messages (like Update commands) for which it looks like you can safely process them multiple times, in which case you might want not to pay the performance overhead there. The thing is, if your logic publishes an event in addition to the regular database work (something that is quite common) and you process the same message twice, you will probably end up publishing the event twice as well.

These duplicates are different in that here we have two distinct messages with different IDs that contain the same business data. This means that recipients of these messages will not be able to filter them out at an infrastructure level anymore.

NOTE: Deduplication abilities in queues

Although the Azure Service Bus doesn’t support distributed transactions meaning you still have the issue mentioned above, Microsoft added the ability to detect and filter out duplicates based on message contents rather than just the ID. This helps quite a bit but it’s important to understand that that doesn’t cover everything for you. Let me explain:

More complex logic

In some of your most important use cases, you may have both entity updates as well as entity creation happening together in your domain model. You might be using some kind of event model (like I wrote about here) to percolate out the information that an entity was created in order to keep your service layer decoupled from the internals of the domain model.

In the callback code from these domain events, you will likely publish out an event on the queuing system containing information like the ID of the entities created as well as other business data. And there’s the rub.

You see, without distributed transactions, you can run into some problematic scenarios:

For example, if you don’t make sure that your event publishing calls to the queuing system include the same transaction object as the one you used when retrieving the original message from the queue, then those calls could “escape” before you know if the database transaction is going to succeed. Deadlocks always happen at the lousiest times. Anyway, if you’re using database generated IDs for your entities, then those IDs will get published out in events despite the database rolling back and your subscribers will now be making decisions on wrong data – not just eventually consistent data.

In this case, processing the message again doesn’t really solve the problem – it just means that you’ll be publishing events with different IDs, so an infrastructure like Azure Service Bus couldn’t really de-duplicate them.

On the other hand, if you do use the same transaction and combine in the infrastructural message ID based de-duplication described above (as identifying duplicate calls for complex business logic is damn hard), you’ll run into another problem.

Consider what would happen if your server crashes right after finishing its database work but before it completes the transaction against the queuing system. When going to retry the message, the infrastructure filtering thing would know not to call your business logic again and that message would be quietly swallowed. Unfortunately, the event publishing calls to the queuing system from the first time the message was processed were rolled back and since your business logic isn’t called again, the event publishing won’t happen again.

Oops.

In closing

I hope I’ve been able to clarify what kind of scenarios distributed transactions solve for you and some of the difficulties in solving them yourself.

Now, to be clear, you could solve these problems by going in-depth on each of your use cases, analyzing the consistency needs and structuring the code differently to address those needs. But give this another thought, if our consistency is dependent on calling otherwise independent APIs in exactly the right order, and that a change in this order would not cause any visible functional effects, what would happen when developers with less expertise maintain this code?

The folks in the event sourcing community have their solution to this which is based on writing their business logic differently. As the adoption of this pattern is still pretty limited (probably still in the Innovator section of the Technology Adoption Curve), it’ll be interesting to see how it holds up with larger teams in the mainstream.

Oh, and in case it wasn’t clear from before, the guys in the REST community haven’t even begun addressing this problem when it comes to server-to-server integration.

We’re working on a solution for this with NServiceBus that won’t require you to change how you write business logic. We’ve got one big release to do before we can roll this in, and that’s coming soon (with all sorts of cool things like support for ActiveMQ and queues in the database). The solution we’ve found is architecturally sound but you’ll have to wait for my next post to hear about it.

Stay tuned.



Service-Oriented API implementations

Monday, December 10th, 2012

gearsIt’s quite common for our systems to need to expose an API for external parties to call that isn’t exactly aligned with our service boundaries – at least, when you follow the “vertical services” model rather than the “layered services” approach. I’ve blogged many times about the problems with layering, so I won’t go into that now beyond to say that you really, REALLY, should avoid it.

A short intro to SOA, done right

In the “vertical services” approach I espouse, you often see components from multiple services deployed to any given endpoint. While these services usually don’t need to communicate with each other at all, occasionally you’ll see them leaving “breadcrumbs” behind for each other – things like UserId or OrderId in the session. What’s especially important is that these IDs are accessible even before the entity is finalized – this enables each service to collect its own data without needing any other service to know about that data.

In an ecommerce environment, we would see one service owning money, another the product catalog (excluding prices, those would be owned by the previous service), another service owning the customers’ payment info (credit cards, etc), and yet another owning shipping addresses – all of these separate from the one that owns the shopping cart. Let’s call these Finance, Catalog, Payment, Shipping, and finally Shopping – just so that we have something to reference later.

The API

While we can do all sorts of cool browser composition with the UI in our own system, enabling each service to collect and display its own information, if we want to expose an API for clients to call, we wouldn’t want to force those clients to have to make a separate call to each service in order to make a purchase. Instead, we’d want something that looks like:

MakePurchase(Guid orderId, Dictionary cart, CreditCardInfo cc, Address shippingAddress)

In case you were wondering, the service which owns the definition of this API is different from all of the above services – it is a service that is primarily technical in nature and is responsible for things like integration and data transformations. I call this service IT/Ops.

Getting the data from the API to the services

So, we don’t want any of our business-centric services to know about anybody else’s data structures, so that leaves it to IT/Ops to pass the data to them. The thing is that we still want to do that in the most loosely-coupled way possible – with messaging being a good candidate for that.

So, what we’ll do is have IT/Ops send a message containing the data to the other services, but with a slight twist.

Here’s what the code would look like with NServiceBus:

Bus.SendLocal(new Order { Id = orderId, Cart = cart,
                          CreditCard = cc, ShippingAddress = shippingAddress });



Why the SendLocal?

So that the components from the other services can all run together with IT/Ops in the same process giving a nice tight deployment model.

UPDATE:

If you’re using a transport like RabbitMQ that is set up as a remote broker, the overhead of going back through the broker might not be worth the improved reliability you’d get by going through messaging. In that case, you might want to consider the Domain Events approach. This would give you a similar level of decoupling but then IT/Ops would need to set up an surrounding transaction, well, that is if you want all the services processing to succeed/fail as one unit. If you don’t, you’d probably be better off just sending messages from IT/Ops to endpoints that host each of the components of the other services.

End Update

Before we get to the services, let me show you the Order class – specifically, the interfaces it implements:

public class Order : ShoppingOrder, PaymentsOrder, ShippingOrder
{
    public Guid OrderId { get; set; }
    public Dictionary<Guid, int> Cart { get; set; }
    public CreditCardInfo CreditCard { get; set; }
    public Address ShippingAddress { get; set; }
}

public interface ShoppingOrder
{
    Guid OrderId { get; set; }
    Dictionary<Guid, int> Cart { get; set; }
}

public interface PaymentsOrder
{
    Guid OrderId { get; set; }
    CreditCardInfo CreditCard { get; set; }
}

public interface ShippingOrder
{
    Guid OrderId { get; set; }
    Address ShippingAddress { get; set; }
}




Each of the above interfaces represents the data that each service cares about. Therefore, each service will provide an assembly that handles that message/data and persists it to its database, like this:


public class ShoppingAPIHandler : IHandleMessages<ShoppingOrder>
{
    public void Handle(ShoppingOrder message)
    {
        //persist to shopping service db
    }
}

public class PaymentsAPIHandler : IHandleMessages<PaymentsOrder>
{
    public void Handle(PaymentsOrder message)
    {
        //persist to payment service db
    }
}

public class ShippingAPIHandler : IHandleMessages<ShippingOrder>
{
    public void Handle(ShippingOrder message)
    {
        //persist to shipping service db
    }
}



Since the Order object being sent is a polymorphic match for all of these interfaces, NServiceBus knows to invoke all of these handlers. By the way, if you care about the order of invocation, then you can control that as well (but I won’t get into that here).

Also, since all of these handler assemblies are deployed to the same endpoint, and the Order object is sent just once, this means that all the handlers will be invoked in a single transaction on a single thread – either all of them succeeding, or all failing. Since they’re all connected on the same Order Id, referential integrity can be preserved as well.

Wrapping up

When you are building a system on SOA principles, you’ll often find that you need a service like IT/Ops to handle data transformation and other broker-centric tasks. While much of SOA is based on the Bus Architectural Style – meaning primarily publish/subscribe interaction between services – that doesn’t mean that your business-centric services cannot have their components deployed in the same process.

I’d go so far as to say that if you aren’t deploying components from multiple services in process with each other at least some of the time then it’s quite likely that your service boundaries are probably incorrect.

Anyway, I hope you found this post interesting. Shout out to Slawek who gave me the idea for this post.

By the way, if you’d like to learn more about these kinds of patterns, the next batch of courses is open for registration – but the early bird prices are almost over, so you’d better hurry.

Register for   Denver CO, USA,     Bad Ems, Germany,     Perth, Australia.



NServiceBus 3.2 Released

Wednesday, May 23rd, 2012

Following on the official announcement, I wanted to talk a bit about this new release – specifically the modeling tools we’ve integrated with NServiceBus.

Drag & Drop? Code-Gen?! Run Away!!

You see, I’ve always been very opposed to draggy-droppy development environments. Also, I’ve had pretty bad experiences with code generation – usually taking the stance that if there was something repetitive that was being handled by code-gen, it would have been better to design the system in such a way that it wouldn’t require anything repetitive.

And yet, here I am, telling you that I think that the draggy-droppy code-gen that we’ve introduced with ServiceMatrix make NServiceBus that much better – not only does it shorten and flatten the learning curve for those looking at NServiceBus for the first time, but it also really improves the productivity of those already experienced with it.

I almost can’t believe I’m saying this, but it is the future.

The current state of things

That being said, it currently is still very much a v1 release – more of an accelerator for setting a new system up quickly than something integrated in the full system life-cycle.

Update:We’ve now get everything updated for VS2012 and would love your feedback. Check out ServiceMatrix.

Here are some things that are on the roadmap for the future:

  1. Making large solutions easier to navigate by integrating a kind of “pivoting view” that shows different dimensions of the solution and the relationships between them instead of the current single-dimensional tree view.Done
  2. Round-tripping – changes to code sync-ing back to the model. Renaming a message or a handler should work whether you go model-first or code-first.
  3. Audit visualizations – taking the results of the previous run from our audit log and making it easy to see who sent which messages to whom, rewinding, fast-forwarding, and replaying the audit log to debug that last execution

I’ll be honest with you – building this stuff is expensive. If we hadn’t gone down the path of commercializing NServiceBus, there was no way we could have gotten this far, let alone have a chance to do all the other things we’re planning.

On Licensing

We’ve made our fair share of mistakes along the way, particularly around licensing.
We’re a bunch of engineers – what did we know about sales?

But we’re learning and are working to get better at it – like introducing a new license calculator.

So, I’d like to take this opportunity to thank the NServiceBus community at large for sticking by us as we make these transitions, our paying customers for voting with their hearts and their wallets for the continued existence of NServiceBus, and the open-source committers who continue to contribute both with their time and their genius.

We couldn’t have done it without you and we really appreciate your support.

Go on then, give it a download, and let us know what you think. There is some nice “getting started” documentation that will take you, step by step, from a blank Visual Studio to a running ASP MVC integrated publish/subscribe solution.



Logically Distributed, Physically Centralized

Sunday, May 6th, 2012

centralized-distributedWhen people pull back the covers on something like MSMQ, particularly its private queues (the way NServiceBus uses it), and they see that MSMQ is storing its messages in C:\Windows\System32, well, they’re not particularly happy.

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

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

So, here’s the thing:

Virtualization

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

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

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

Databases too

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

Think about that for a second.

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

In closing

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

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

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



   


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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
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“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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