Category Archives : Architecture


The SOA Manifesto – Pointlessness Manifested

You know what the Agile Manifesto doesn’t have? Video of a “very formal ceremony” announcing said manifesto. Instead, we just have artistically rendered picture of what sure looks like Martin Fowler pointing at a white board while some of the other original signatories look on. Sure, it’s a cool picture, but wouldn’t it have been much cooler if they had captured that moment on video instead? Especially if it was video of them all standing around looking vaguely uncomfortable while photographers took their picture and someone gravely read the manifesto to give it artificially inflated importance.

I only watched ten seconds of the SOA Manifestoannouncement video before I realized there’s nothing to see here, move along, just a bunch of navel gazing from the usual SOA suspects.

Seriously, if you having a big announcement about how cool, earth shattering, significant or, hell, even interesting your manifesto is, then it’s not any of those things. It’s a waste of my time.

Then I noticed that my previous manager and personal friend John deVadoss is one of the signatories. I have metric tons of respect for John, so I gave the SOA Manifesto a second chance.

It lost me at the second sentence.

Service orientation is a paradigm that frames what you do. Service-oriented architecture (SOA) is a type of architecture that results from applying service orientation. We have been applying service orientation to help organizations consistently deliver sustainable business value, with increased agility and cost effectiveness, in line with changing business needs.

Are you frakking kidding me? “Service-oriented architecture (SOA) is a type of architecture that results from applying service orientation.” Who the hell came up with that? I didn’t realize the International SOA Symposium had a Department of Redundancy Department.

When you define SOA in terms of SO, then you can’t possibly score well on the practicality quotient.

The rest of the manifesto isn’t much better. What made the Agile manifesto great IMO was that it ran counter to “common” beliefs like “changing requirements late in the process is bad” and “shipping software cycles should take years”. Sure, we all realize how right those Agile manifesto guys were now, but at the time it was the next best thing to heresy for many organizations. Those guys were agents of change. And I mean real change, not “this will help me sell books” change.

SOA manifesto on the other hand is basically repackaged common sense. Stuff like “Recognize that SOA ultimately demands change on many levels” and “The scope of SOA adoption can vary. Keep efforts manageable and within meaningful boundaries” Any help figuring out what that change is or what the scope should be? Nope. Thanks for the advice guys, but I had your so called “Guiding Principles” figured out long ago.

But hey, I’m sure the manifesto will help Thomas Erl et. al. sell more SOA books. So, I guess from that perspective it’s mission accomplished.


The Last Mile of the Internet

Christian Weyer makes a great comment on yesterday’s post about the barbarian rediscovery of async messaging:

But how do these two toolkits solve the NAT/Firewall issue? Without a solution to this they are pretty much useless in breadth usage.

Simply put, they don’t. Frankly, they don’t even try. And I agree with Christian that the NAT/Firewall issue makes any async messaging based approach useless for clients. It’s kind of like the last mile problem in the telco/cable industries – you’ve got this great capability in the center, but you can’t leverage its full potential because of the massive effort it takes to push that capability all the way to the edge of the network.

Dave Winer has been pretty explicit with his RSS Cloud work: “The goal is to have a Small Pieces Loosely Joined equivalent of Twitter.” PubSubHubbub doesn’t mention Twitter by name, but the protocol spec specifically says “Polling sucks. We think a decentralized pubsub layer is a fundamental, missing layer in the Internet architecture today”. Both specs have a fundamental design that looks like this:

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This picture leaves out multiple publishers and subscribers and the subscriber registration process, but you get the basic idea. And it all works great assuming that both the subscriber and the pub/sub infrastructure can accept incoming connections. While that seems like a fairly safe assumption for infrastructure pieces, it is clearly a faulty assumption for any subscriber running locally on a client machine. Client machines primarily live behind firewalls at the office, behind NAT routers at home or on mobile wireless network – all of which disallow most if not all incoming connections. In other words, this works just fine for server subscribers (like, say Google Reader) but not for client subscribers (like, say TweetDeck).

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As far as I can tell, the only way to enable client subscribers to play in this async messaging world is via some type of relay service. Any other solution I can think of depends on mass adoption of new technology, which as I mentioned in my last post is nearly impossible.

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In this approach, the client subscriber makes an outbound connection to some type of relay infrastructure, which in turn creates a endpoint on the public internet for that client. Registration for pub/sub happens as normal, using the relay endpoint as the notification URL. Then, when a message arrives on the relay endpoint, it’s sent back down the outbound connection to the client.

The relay approach is technically feasible – it’s used in many places today. Exchange DirectPush uses this approach to support real-time delivery of mail to mobile devices – though the relay capability is built directly Exchange client access servers rather than available as a separate service. The .NET Service Bus – part of Windows Azure – provides a hosted relay infrastructure that anyone can leverage (though their support of non-windows platforms is pretty weak). I haven’t worked with it, but it looks like Opera’s new Unite platform includes a relay service as well (note, they call it a proxy service). Nice thing about Opera Unite is the async messaging infrastructure is built right into their browser, though you could achieve something similar in any browser using Flash or Silverlight.

Yes, having to relay messages sucks. But the question is, which sucks worse: polling or relaying?


Async Messaging and the Barbarian Hordes

At PDC 1996, Pat Helland did a six minute bit where he compared personal computing to the sacking of Rome and Microsoft Transaction Server to the Renaissance. It was called “Transaction Processing and the Barbarian Hordes” and in my opinion it should be required viewing for everyone in the tech industry.

Of course, the tech industry has changed significantly since PDC96. In particular, personal computing has become the new “Classical Rome” and web developers are the new barbarians. Just as Microsoft rediscovered transaction processing in the 90’s, it seems that RESTifarians are on the verge of rediscovering asynchronous messaging.

“The internet has been dead and boring for a while now.  It has reached a point of stability where flashes of technological creativity are rare, but every now and then some new technology can put a spark back in the ole gal (no sexism intended).

If you haven’t heard of WebHooks or PubSubHubBub its about time you did. Both are designed to  simplify and optimize the web.”

Mark Cuban, The Internet is about to change

Not to put too fine a point on it, but these “flashes of technological creativity” that Mark’s going gaga over aren’t new at all. Both Web Hooks and PubSubHubbub are essentially async messaging, the oldest form of messaging in the history of networking. But just as personal computing ignored the importance of transaction processing for a long time, REST has long ignored the importance of async messaging. Instead, web development has instead been focused exclusively on request/response – something I’ve struggled with for quite some time. But the rise of Twitter has driven many people to realize that something I’ve known since 2003: “In order to truly evolve syndication…we need to break free of the synchronous polling model.” [1]

imageI love the slogan from this Web Hooks presentation: “so simple you’ll think it’s stupid”. Web Hooks aren’t stupid – far from it – but they certainly are simple. They’re basically callbacks – which Web Hooks creator Jeff Lindsay readily acknowledges – invoked across the network using standard REST technology like HTTP and XML or JSON. The canonical webhook examples are Paypal Instant Payment Notification and GitHub Post-Receive Hooks. In both cases, you register a custom notification URL with the system in question. Then, when something specific happens in the system, a message gets POSTed to the registered URL. In some scenarios, it’s a simple notification. For example, when GitHub receives a commmit push, it POSTs a JSON message about the commit to the registered URL. In other scenarios, the initial message is the start of an async conversation – the system expects you to POST a message back to them sometime in the future. For example, when a customer makes a payment, PayPal POSTs a message to the URL you registered. You then confirm the payment by posting a message back to a well known PayPal URL.

Note, by the way, that both of these canonical examples depend on async messaging. GitHub isn’t going to do anything with a response anyway, so there’s no point in sending them a response. PayPal, on the other hand, is expecting a response. Yet, they use async messaging instead of an arguably simpler HTTP request/response operation. They do this for same reason WS-Transaction is the Anti-Availability Protocol – the last thing you want to do is lock up precious resources in your system waiting for some nimrod on the other side of the Internet to respond to a request you sent. Instead you what PayPal does – send an async message, listen on a separate channel for a response, correlate the messages explicitly via some kind of conversation identifier and release your precious resources to do other work while you wait for the response.

image As for PubSubHubbub, it’s focused on real time delivery of new information. Dave Winer’s recent RSS Cloud efforts focus on real-time notification as well. In both cases, instead of subscribers polling a given RSS feed for changes every X amount of time, they register for notification when the feed is updated. This is very similar to the way GitHub uses async messages for commit push notification as described above.

imageBoth PubSubHubbub and RSS Cloud include an intermediary that’s responsible for managing the list of current subscribers and relaying the notification when the publisher makes a change.  Honestly, I’m not a fan of the Hub/Cloud intermediary – it feels a little too ESB-like to me. However, since it’s only relaying notifications it receives without transformation, I can live with it. Besides, there’s no reason why a publisher can’t act as it’s own hub. The vast number of blogs and twitter users have so few subscribers that the extra layer of abstraction is probably not worth it. On the other hand, if you’re going to run a notification hub for the largest users, you might as well use it for smaller ones as well.

While I think Mark’s laid the “new technology” hype on pretty thick, I do think he hits the nail on the head regarding the major new business opportunities that can come from adopting the heretofore ignored async messaging model on the web:

“This could be an open door for the content business…Using The Associated Press as an example, AP could post their stories to a HUB. In realtime, the HUB can update member websites so that they will always have information first, before any aggregator. It may not take long for aggregators to recognize the new data on the member sites, but they won’t have it first.

The New York Times could do the same thing. Subscribers could get everything first, in realtime. Then after some delay which might be 1 minute, it might be 30 minutes depending on what the paper thinks is the value related to timeliness, it could post on the website and on twitter and facebook as updates. Would NY Times online readers pay $1 a month to be guaranteed that they get their news first, before anyone else ? I dont know.

In the sports world, text based play by play websites could be updated in realtime rather than pulling every 30 seconds or requiring the user to hit refresh every few seconds.”

Arguably, this opportunity is easier to realize precisely because async messaging isn’t new technology. Getting people to adopt a new technology is incredibly hard. It’s much easier to get people to adopt a new pattern for using an existing technology. And async messaging has been possible as long as the web has been in existence.

Web Hooks and PubSubHubbub are long overdue but very welcome steps forward in the evolution of the Internet. I wonder what the barbarians will rediscover next?


[1] Of course, writing a prediction like this is a far sight from actually implementing it. If I had actually put some engineering effort behind this in 2003, maybe I’d be a household name in the tech community by now. On the other hand, I said some things in that same post that have turned out to be spectacularly incorrect (“Indigo is going to make Longhorn a great platform for SOA”) so it probably wouldn’t have made much of a difference.


Architecture Astronauts and Over Engineers

Since it’s apparently Architecture Week™ [1] here at DevHawk, here’s another of my favorite Dilbert cartoons of all time – relevant to the discussion at hand.

Dilbert.com

Two interesting comments on yesterday’s post:

Architectural thinking is a necessary (and very important) part of software development – but beyond the systems level (which is systems administration and not software architecture) I have a hard time seeing divorcing architectural thinking from the actual development as anything but a terrible thing. Although I see that your definition of architecture (at the functional level) does not match my caricature of the ‘architecture astronauts’ which I do think can be endemic in languages that encourage additional layers of architecture. [Michael Foord]

So based on the definition of architecture I’m reading into your post, you wouldn’t consider the choice of object-oriented versus functional programming styles from an architectural perspective? I’m trying to understand what level of architecture you mean here. Like Michael, I usually think of architecture even down into the implementation patterns level (hence the architecture astronauts), but that seems to be included in what you might be calling an engineering concern. [Ryan Riley]

Let me be very clear. Using my definition, there is no such thing “architecture even down into the implementation patterns level”. I’d argue that the implementation patterns level is engineering, not architecture. From what I’ve seen, the terms “architecture” and “engineering” tend to be used interchangeably in the software industry, and frankly I think that’s a mistake. I said as much in yet another post I wrote four years ago:

Architecture is the intersection between business and IT.

If a decision doesn’t effect a business person, it’s not an architecture decision. I’m not saying it’s not important – I think the role of the software engineer is critical in large-scale enterprise system design and construction. And I will readily admit that often a single person is responsible for both architecture and engineering. But that doesn’t make them the same activity. As long as we continue to confuse the two disciplines, we hold them both back.

Michael and Ryan (or anyone else for that matter) are welcome to disagree with my definition of architecture. I often joke that if you asked ten architects to define “architecture”, you’d get twelve answers. But that’s my definition and I’m sticking to it.

But what of the Architecture Astronauts? Both Michael and Ryan mentioned them. Unsurprisingly, I think that term is used too broadly as well. If you go back and read Joel’s original post of Architecture Astronauts, there wasn’t much reference, if any, to the implementation layer at all.

The Architecture Astronauts will say things like: “Can you imagine a program likeNapster where you can download anything, not just songs?” Then they’ll build applications like Groove that they think are more general than Napster, but which seem to have neglected that wee little feature that lets you type the name of a song and then listen to it — the feature we wanted in the first place. Talk about missing the point. If Napster wasn’t peer-to-peer but it did let you type the name of a song and then listen to it, it would have been just as popular

[Joel on Software, Don’t Let Architecture Astronauts Scare You]

I feel that my definition fits very well with the way Joel writes about architecture in this paragraph. The Architect Astronaut is trying to solve a real business problem – people need access to information besides music. But the mistake they make is thinking they can solve multiple problems with a single solution. So they abstract higher and higher until they’ve lost sight of the original problem and can only focus on the abstractions. If you look at what Joel has to say about technologies like Hailstorm and Jini, you see the same pattern emerge.

This isn’t to say that similar problems of over-abstraction don’t happen at the implementation layer – they do. But they happen for very different reasons. Astronaut Architects are trying to solve multiple problems with a single solution. But when over-abstraction happens at the implementation level, it because someone thought they could predict the future.

We’ve all seen our fair share of over-engineered systems that introduce significant unneeded complexity on the off chance that the development team can successfully predict the kind of change likely to come in the next version of the product. Invariably, the team’s precognitive abilities are revealed to be as poor as everyone else’s, so they’re left with a bunch of extra layers of software cruft that has to be maintained but provides zero additional value to the system. I’ve blogged about that problem before as well: Kitchen Sink Variability.

Since I’m big on keeping the terminology of architecture and engineering separate, then I’d argue that we need a different term than Architecture Astronaut for people who want to introduce additional layers of abstraction at the implementation layer on the off chance that they don’t suck at precognition. Since we call such systems over-engineered, wouldn’t that make the people who build them “Over Engineers”?


[1] It’s like Shark Week, but with white boards and even more terrifying.


Dynamic Languages in Architecture

In the comments from yesterday’s post, IronPython MVP and author extraordinaireMichael Foord asked:

Has your view on architecture as a discipline separate from coding changed since working with dynamic languages?

In a word:“No” (though as always, I reserve the right to be wrong and/or convinced otherwise.)

When I was an architect, I tried very hard to treat it as a “discipline separate from coding”. To use my last post as an example, building a central repository of system audit information is an architectural decision. A bad one IMHO – at least the way Dilbert’s PHB described it – but an architectural decision all the same. It was a decision about what kind of system to build, part of an overall application portfolio, as opposed to a decision about how to build the system.

I’ve held this opinion of architecture for a long time. Four years (and three jobs) ago, I wrote the following:

IMO, building a system that has a set of functional requirements (track customers, process orders, etc) and non-functional constraints (sub-second response time, support 10,000 concurrent users, use Microsoft Windows platform, etc) is an engineering problem. Coming up with the lists of functional requirements and non-functional constraints is the architecture problem.

Working with dynamic languages has dramatically changed my view of engineering and design of individual systems. But from the pure architecture perspective, I want to be able to treat individual systems as black boxes as much as possible. That means the programming language is an implementation detail that shouldn’t matter to the architect.

Note the significant bet-hedging language in the paragraph above. I’m using phrases like “shouldn’t matter” and “as much as possible” because we all know that there’s no such thing as a “pure architecture perspective”. Unlike building architecture, software architecture is in constant flux at every level. At the enterprise level, there are always new regulatory obligations, new competitors and new partners to consider. At the end-to-end process level, there are always new systems or new version of existing systems coming on line. And at the individual system level, there are always new – or at least new versions – of tools, frameworks and languages being released.

Once you introduce time into your architecture perspective, individual system engineering will affect the overall architecture, since system engineering affects the rate of change. Language choice will certainly have some engineering impact. However, in my experience language choice is rarely high on the list of concerns relative to things like project scope and team experience.

So my “No” answer to Michael’s question is predicated on the following:

  • As an architect, I want to consider individual systems as black boxes where implementation details like language choice are completely irrelevant.
  • As a practical architect, I realize that some system implementation details are relevant – especially over time – but in my experience language choice isn’t one of them.

On the other hand, most IT shops try to standardize on one programming language – certainly MS IT did – so maybe language choice would be more architecturally relevant in a mixed language shop. I’d love to hear from folks who have multiple standard languages in their IT shop – especially if you have both static and dynamic languages on your standards list.