Entries Tagged 'soa' ↓

This is a few months old, but Werner Vogels republishes the Amazon.com Shareholder Letter. A summary of how the quintessential 21st century company views its competitive advantage:

1. Service Oriented Architecture
2. Distributed state management
3. Decision management

Regarding Service Orientation:

Our technologies are almost exclusively implemented as services: bits of logic that encapsulate the data they operate on and provide hardened interfaces as the only way to access their functionality. This approach reduces side effects and allows services to evolve at their own pace without impacting the other components of the overall system. Service-oriented architecture — or SOA — is the fundamental building abstraction for Amazon technologies. Thanks to a thoughtful and far-sighted team of engineers and architects, this approach was applied at Amazon long before SOA became a buzzword in the industry. Our e-commerce platform is composed of a federation of hundreds of software services that work in concert to deliver functionality ranging from recommendations to order fulfillment to inventory tracking. For example, to construct a product detail page for a customer visiting Amazon.com, our software calls on between 200 and 300 services to present a highly personalized experience for that customer.

In systems architecture, there are rarely any right answers – mostly just trade offs between one solution or another. In such cases it helps to bear in mind some fundamental principles as a guideline. One principle I often use is cost vs. benefit. Another useful principle is to minimize coupling between systems. Coupling is pervasive and leads to a kind of inertia in enterprise systems. Newton discovered that inertia prevents change and if there is one thing that enterprises struggle most with, it’s change.

Taking a leaf from the Agile playbook, a group of SOA thought leaders has put together the SOA Manifesto, a succinct list of SOA principles and preferences to guide Service Oriented Architecture. Great work!

(I could comment further, but it speaks for itself).

Go visit and find out.

The title of the InfoQ article, “Economics of Service Orientation” caught my interest, but unfortunately I was left disappointed. I felt that the article missed the mark somewhat and also missed some of the important costs of Service Orientation in its eagerness to concentrate on the benefits.

In my view, the real economics of SOA is about how many times you pay for the same function.

In the world of packaged applications you have very coarse control over the number and bundling of the functions that you have available. If you buy a packaged application, then you typically buy a bundle of functions or capabilities – some of these hopefully will be functions that you need, yet others will be functions that you don’t need.

An example of this is if you buy a billing application which has inbuilt functionality for handling customer contact details. You may not need customer contacts in your billing application because it already exists in your CRM (for example). However, as delivered, the billing application requires its own proprietary customer contact details module because it is incapable of working with a 3rd party’s CRM data. So there are a bunch of costs associated with purchasing a packaged application:

1. The cost of the functionality that you require.
2. The cost of the functionality that you don’t require (the vendor charges licence and support fees for the whole package, not just the bits you really want to use).
3. The infrastructure cost of hosting all this functionality – required and not required.
4. The cost of integrating the functionality you require into your business processes.
5. The cost of integrating and potentially mitigating the functionality that you don’t require.

If we consider cost 5) in the context of my example. Even though you have a perfectly good CRM, the billing system requires contact details to be managed within its own application database, so you have to integrate your CRM with the billing application. There may be side-effects of this integration which need to be mitigated. You may need to invent whole new business processes to manage duplication between two or more systems and the inevitable synchronization problems that arise.

In an SOA utopia, there is more fine grained control over the functions that you acquire from a vendor. In particular you can buy only the functions that you need and then have them plug into other services in your information infrastructure. This saves a number of costs:

1. You only pay for the function that you require
2. You don’t pay for the functions that you don’t require
3. You only pay to host the functionality you have bought – not a bunch of tag-alongs. And if your function is remotely hosted, the costs of hosting the new functionality may be very low.
4. You pay only the cost of integrating the required functionality into your business processes
5. You don’t have to pay to integrate and mitigate functionality you don’t require

So the economic value of SOA is in the finer granularity with which you can manage the cost of your IT functionality. The job of the enterprise architect moves from managing a portfolio of applications – complete with duplicates and overlaps – to one of managing services or functions, with hopefully minimal duplicates and overlaps.

But this picture wouldn’t be complete without considering the additional overheads required for a well functioning SOA. Architectural standards and governance are required to ensure that you buy the right services at the right time and that the services can be integrated properly into your business processes. You should then add in costs associated with:

• There is a cost for running an enterprise architecture function – managing standards and governance.
• The cost of acquiring a specific function may be higher because of the additional planning and research required to get the “right” function for your business processes and to fit into your enterprise services framework.
• The integration cost of exposing functions as services is generally going to be higher than just building a point integration. This is because of the greater degree of planning involved with providing a service in a reliable and re-usable manner.

But hopefully the additional cost of architectural governance and standards should be offset by the savings in managing services as opposed to packaged applications.

As a final note, it’s interesting to note that the economic model is similar for the vendors as it is for their customers. This is why many packaged application vendors are hopping on the bandwagon of SOA. These vendors have acquired applications with overlapping functionality and require a more fine-grained approach for managing and selling their functionality.

In my opinion, coupling is the most fundamental attribute of a system architecture and tight coupling is probably the most common architectural problem I see in distributed systems. The manner in which system components interact can be a chief determinant of the scalability and reliability of the final system.

So I really like Ian Robinson’s post on Temporal and Behavioural Coupling where he uses two coupling dimensions and the inevitable magic quadrant to classify systems based on their degree of temporal and behavioural coupling.

See Ian’s post for the slick professional graphics, but to summarise – event-oriented systems with low coupling  occupy the “virtuous” third quadrant of the matrix. Conversely the brittle “3-tier” applications that many of us struggle with, occupy the “evil” first quadrant where coupling in both dimensions is high.

However I’m a little miffed to see no mention of my favourite “document-oriented message” in Ian’s diagram. As Bill Poole writes; document messages have lower behavioural coupling than command messages, but more than event messages. So would you put document-oriented messages near the middle top of the matrix between command-oriented and event-oriented messages? Unfortunately that would break the symmetry. But it also highlights another problem.

Any type of message – document, command or event-oriented could temporally be tightly or loosely coupled. Temporal coupling is more a property of the message transport than of the message type. So I suggest that the two coupling dimensions are characterised as follows:

• Temporal coupling – characterised by message transport from RPC (tight coupling) through to MOM (loose coupling).
• Behavioural coupling – characterised by the message type from event-oriented (tight) through document-oriented to event-oriented (loose).

It so happens that distributed 3-tier systems generally employ both command-oriented messages and RPC transports – hence making them inherently “evil”. Whereas events (being asynchronous)  are naturally virtuous by typically being carried over MOM transports (it’s difficult to request an event notification).

Between heaven and hell, it is in the murky mortal realms of SOA where we need to be constantly mindful of the interactions between message type and transport – lest our system ends up in limbo.