Udi Dahan   Udi Dahan – The Software Simplist
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Archive for the ‘NOSQL’ Category



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…



Queries, Patterns, and Search – food for thought

Sunday, April 28th, 2013

fishWith all the talk of CQRS, the area that doesn’t get enough treatment (in my opinion) is that of queries. Many are already beginning to understand the importance of task-based UIs and how that aligns to the underlying commands being sent, validated, and processed in the system as well as the benefits of messaging-centric infrastructure (like NServiceBus) for handling those commands reliably. When it comes to queries, though, it isn’t nearly as well understood what it means for a query to be “task based”.

Starting with CRUD

Let’s start with a traditional CRUD application and work our way out from there.

In these environments, we often see users asking us to build “excel-like” screens that allow them to view a set of data as well as sort, filter, and group that data along various axes. While we might not get this requirement right away, after some time users begin to ask us to allow them to “save” a certain “query” that they have set up, providing it some kind of name.

That, right there, is a task-based query and it is the beginning of deeper domain insight.

Pattern matching

Any time a user is repeatedly running the same query (this can be once a day or some other unit of time) there is some scenario that the business is trying to identify and is using that user as a pattern-matching engine to see if the data indicates that that scenario has occurred.

It’s quite common for us to get a requirement to add some field (often a boolean or enum) to an entity which defaults to some value and then see that same field used in filtering other queries. These measures are sometimes instituted as a temporary stop-gap while a larger feature is being implemented, though (as the saying goes) there is nothing more permanent than a temporary solution.

Where we developers go wrong

The thing is, many developers don’t notice these sorts of things happening because we don’t actually look at the kinds of queries users are running.

One excellent technique to better understand a domain is to sit down with your users while they’re working and ask them, “what made you run that query just now?”, “why that specific set of filters?”.

What I’ve noticed over the years is that our users find very creative ways to achieve their business objectives despite the limitations of the system that they’re working with. We developers ultimately see these as requirements, but they are better interpreted as workarounds.

I’ll talk some more about how a software development organization should deal with these workarounds in a future post, but I want to focus back in on the queries for now.

Oh, and don’t get me started on caching or NoSQL, not that I think that those tools don’t provide value – they do, but they’re only relevant once you know which business problem you’re solving and why.

Not all queries are created equal

Even before bringing up the questions I described in the previous section, any time you get query-centric requirements the first question to ask is “how often will the user be running this specific query?”.

If the answer is that the specific query will be run periodically (every day, week, etc), then drill deeper to see what pattern the user will be looking for in the data. If the person you’re talking to doesn’t know to answer that question, then go find someone who does. Every periodic query I’ve seen has some pattern behind it – and in my conversations with thousands of other developers over the years, I’ve seen that this is not just my personal experience.

But there is a case where a query does get run repeatedly without there being a pattern behind it.

I know this sounds like I’m contradicting myself, but the distinction is the word “specific” that I emphasized above.

There are certain users who behave very differently from other users – these users are often doing what I call research, i.e. the “I don’t know what I’m looking for but I’ll know it when I see it” people.

These researchers tend to repeatedly query the data in the system however they tend to run different queries all the time. This is the reason why traditional data warehouse type solutions don’t tend to work well for them. Data warehouses are optimized for running specific queries repeatedly.

Keeping the Single-Responsibility Principle in mind – we should not try to create a single query mechanism that will address these two very different and independently evolving needs.

And now on to Search

Search is a feature that is needed in many systems and whose complexity is greatly underestimated.

While the developer community has taken some decent strides in understanding that search needs to be treated differently from other queries, the common Lucene/Solr solutions that are applied are often overwhelmed by the size of the data set on which the business operates.

The problem is compounded by our user population being spoiled by Google – that simple little text box and voila, exactly what you’re looking for magically appears instantaneously. They don’t understand (or care) how much engineering effort went into making that “just work”.

Lucene and Solr work well when your data set isn’t too large, and then they become pretty useless as the quality of their results degrades. The thing is that many of us in IT tend to work on projects where we have an unrealistically small data set that we use to test the system and, at these volumes, it looks like our solutions work great. But if you have 20 million customers, do you think a full text search on “Smith” is going to find just the right one?

Larger data sets require a relevance engine – something that feeds off of what users do AFTER the query to influence the results of future queries. Did the user page to the next screen? That needs to be fed back in. Did they click on one of the results? That needs to be fed back in too. Did they go back to the search and do another similar search right after looking at a result – that should possibly undo the previous feedback.

And that’s just relevance for beginners.

You know what makes Google, you know, Google? It’s that they have this absolutely massive data set of what users do after the query that informs which results they return when. You probably don’t have that. That and search is/was their main business for many years – I’m betting that it’s not your main business.

You should discuss this with your stakeholders the next time they ask for search functionality in your system.

In closing

I know that the common CQRS talking points tell you to keep your queries simple, but that doesn’t mean that simple is easy.

It takes a fair bit of domain understanding to figure out what the queries in the system are supposed to be – what tasks users are trying to achieve through these queries. And even when you do reach this understanding, convincing various business stakeholders to change the design of the UI to reflect these insights is far from easy.

It often seems like the reasonable solution to give our users everything, to not limit them in any way, and then they’ll be able to do anything. What ends up happening is that our users end up drowning in a sea of data, unable to see the forest for the trees, ultimately resulting in the company not noticing important trends quickly enough (or at all) and therefore making poor business decisions.

Even if your company doesn’t believe itself to be in “Big Data” territory, I’d suggest talking with the people on the “front lines” just in case. Many of them will report feeling overwhelmed by the quantity of stuff (to use the correct scientific term) they need to deal with.

It’s not about Lucene, Solr, OData, SSRS, or any other technology.

It’s on you. Go get ’em.



UI Composition Techniques for Correct Service Boundires

Saturday, June 23rd, 2012

PrismOne of the things which often throws people off when looking to identify their service boundaries is the UI design. Even those who know that the screen a user is looking at is the result of multiple services working together sometimes stumble when dealing with forms that users enter data into.

Let’s take for example a screen from the Marriott.com online reservation system (below). This screen collects information about the guest staying at the hotel (name, phone number, address, etc) and credit card information.

marriott

While we might have wanted to keep guest information in a separate service from the credit card information (which may very well be the corporate card of someone responsible for travel), the above screen would seem to indicate that the data would be collected together, validated together, and would also have to be processed together.

The traditional way

In standard layered architectures you would have all the data submitted by the user passed in a single call from a controller to some “service layer” (possibly running on a different machine), which would then persist that data in one transaction.

Even if some attempt was made to separate things out, there likely would be some “orchestration service” that received the full set of data and it would make calls to the other “services”, passing in the specific data that each “service” is responsible for.

I am putting quotes around the word “service” to indicate that I don’t consider these proper services in the SOA sense (as they lack the necessary autonomy) – they are more like functions or procedures, whether or not they’re invoked XML over HTTP is besides the point.

What to do?

Like so many other things, the solution is simple but a bit counter-intuitive as it doesn’t follow the way most web development is done, i.e. one submit button => one call to the server.

Let’s say the “Red” service is responsible for guest information and the “Blue” service is responsible for credit card data. In this case, each service would have its own javascript come down with the page and that script would register itself for a callback on the click of the submit button. Each service would take the data the user entered into its part of the page and independently make a call to “the” server (could be to 2 separate servers) where the data is persisted (potentially to 2 different databases).

This raises other questions, of course.

Now that the data submitted is being processed in 2 transactions rather than just one, we may need to figure out how to correlate the data. In this specific case, it’s not such a big deal as there is no direct relationship between the guest and the credit card – both need to be independently correlated to some reservation ID.

That reservation ID would likely have been “created” on a button click on a previous screen by some other service. The reason why I put the word “created” in quotes is that this could be as simple as having the client generate a new GUID and put that in a cookie (which would cause the reservation ID to end up being submitted along with subsequent requests). Another alternative would be to put the reservation ID in the session.

It’s quite possible that the reservation ID would only be persisted much later in the service that owns it when the user actually confirms the reservation on the website.

In any case, what we can see is that each of the commands of our respective services can now be processed independently of the others in an entirely asynchronous fashion thus vastly improving the autonomy of our services.

Some words on CQRS

This style of UI composition where services leverage javascript code running in the browser isn’t technically difficult in the slightest. The rest of the implementation of each service – having a controller that takes that data and passes it on for persistence can be quite simple.

I’d say even more strongly, most of the time you shouldn’t need to use any fancy-dancy messaging to get that data persisted – that is, unless you’re still stuck with the big relational database behind 23 firewalls type data tier. Embrace NoSQL databases for the simplicity and scalability they provide – don’t try to re-invent that using messaging, CQRS, persistent view models, event-sourcing, and other crap.

There are other very valid business reasons to embrace CQRS, but they have nothing to do with persistence.

Also notice, this is all happening within a service boundary / bounded context.

In closing

If you aren’t leveraging these types of composite UI techniques, it’s quite likely that your service boundaries aren’t quite right. Do be aware of the UI design and use it to inform your choices around boundaries, but be aware of certain programming “best practices” that may lead you astray with your architecture.

Also, if you’re planning on coming to my course in Toronto to learn more about these topics, just wanted to let you know that there’s one week left for the early-bird discount.

Finally, it’s good I have a birthday that comes around once a year to remind me that my time here isn’t unlimited and that I had better get off my rear and do something meaningful with the time I do have. If you get value from these posts, leave a comment or send me a tweet to let me know – it does wonders for my motivation.

Thanks a bunch.



Common CQRS Abuses

Sunday, February 26th, 2012

Abuse #1

“I’m using CQRS because I need to scale.”

While CQRS may be more scalable than other more traditional architectures, the use of asynchronous communication often complicates the user interaction model causing users to not see the changes they made to data in the UI until later. Trying to compensate for this (by writing even more code) digs one deeper into the complexity hole.

When I point to non-collaborative subdomains and state “You don’t need CQRS for that”, the reason is that in these areas you don’t tend to have much read/write contention. While multiple users/actors may be working in parallel, they don’t touch the same set of data (or do so only very rarely).

In these environments, all you need is a scalable data storage technology – something designed to scale-out (unlike most relational databases). This can take the form of NOSQL databases like HBase and Cassandra. Often all you need is the UI to query that directly and show the results, and the same goes for persisting the data back – possibly with some basic validation and calculation code on the side.

No commands, events, DTOs, publish/subscribe, domain model, etc.

As Ayende says – JFHCI, just f-ing hard code it.

You’d be surprised how much of your data this approach can apply to.

With the time you save on all the less important stuff, you’ll have more time to apply CQRS the right way for the high-value/high-complexity parts of your system.

***

Just a final note, as registration for my course in New York is coming to a close in 2 weeks, I wanted to let you all know that the price for the course will be going up this April, after the course in Sydney. The reason for this is that the courses I run myself (at the current rate) have been cannibalizing attendees from the partner companies I do the course with.

I’ll be providing significant discounts to independent consultants (and others paying their own way) to try to keep things fair. Hope to see you there.

Go to the registration page.



   


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Recommendations

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.

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“Udi, one of the great minds in this area.
A man I respect immensely.”





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"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."

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“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.
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“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.”

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“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.
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“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.
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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.”

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“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.”

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Awesome. Just awesome.

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“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.
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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.
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“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.

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“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.
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On the personal level - Udi is a great communicator and can persuade even the most difficult audiences (I was part of such an audience myself..) by bringing sound explanations that draw on his extensive knowledge in the software business. Working with Udi was a great learning experience for me, and I'll be happy to work with him again in the future.”

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

Consult with Udi

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

97 Things Every Software Architect Should Know



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