Given my years at ZapThink, fighting to help architects understand what Service-Oriented Architecture really was and how to get it right, it’s no surprise that many people ask me this question.

If you took my SOA course, you can probably guess my answer: it depends.

Even to this day we don’t have a universally accepted definition of SOA. But even if we did, we’d also have to figure out what “SOA done wrong” means, in order to contrast microservices with it.

However, the question “Are Microservices ‘SOA Done Right’?” itself is a mix of apples and, well not oranges – more like confusion between apples and best practices for running an orchard.

What we really mean to ask is whether microservices architecture is SOA done right. But then, of course, we’d have to figure out what microservices architecture was. And if you think defining SOA is difficult, pinning down microservices architecture is unquestionably frying pan into fire time.

The last thing I want to do, however, is make this Cortex into a discussion of the definitions of terms. True, defining terms is what architects love to do best – even though they never end up agreeing. It’s no wonder that the collective term for these folks is an argument of architects.

stationSOA Done Wrong

In my Bloomberg Agile Architecture Certification course I paint the difference between what I like to call first generation and second generation SOA. The first generation centered on the role of the ESB, and sported Web Services as the primary type of service.

It might well be argued that this middleware-heavy, XML-laden approach to SOA was SOA done wrong, and to be sure, many times it was – but then again, on occasion a particularly hardworking and indubitably masochistic architecture team actually got this stuff to work.

Second-generation SOA is REST-based, favoring lighter weight approaches to moving messages around than the heavyweight ESBs that gave SOA a bad rep. Note, however, that the rise of REST-based SOA predates the microservices wave – so only through some convoluted revisionism might we call this approach microservices architecture.

We might therefore also ask whether this second generation, REST-based SOA was SOA done wrong as well. Once again, the answer is sometimes yes, sometimes no.

RESTful interfaces clearly cleaned up a lot of the mess that Web Services left behind. But implementing properly abstracted, governed service interfaces in the absence of traditional middleware often proved to be surprisingly difficult.

ESBs might be SOA crutches to be sure, but don’t forget, the alternative to crutches is often falling on your face.

Reinventing the Service

Fortunately, the microservices story isn’t about ESBs. It’s about services. Starting from the earliest days of first-generation SOA and running throughout SOA’s RESTful days, the word service meant a contracted software interface. In other words, a service abstracted the underlying software rather than being software itself.

Microservices, in contrast, rethink the notion of service altogether. No longer is a service a contracted software interface at all. Instead, a microservice is a unit of execution.

I like to define a microservice as a parsimonious, cohesive unit of execution. By unit of execution I mean that microservices contain everything from the operating system, platform, framework, runtime, and dependencies, packaged together. And naturally, microservices are fully encapsulated, supporting interactions entirely through their (usually RESTful) APIs.

See my recent BrainBlog post for a deeper discussion of microservices (in particular, what I mean by parsimonious and cohesive) – as well as some insight into how microservices architecture is supposed to work. But even with my thought-provoking connected car scenario from that post, we still have the questions of the day: is such a microservices architecture SOA? And if so, is it SOA done right?

Microservices typically have RESTful interfaces, and we’re likely to have sufficient metadata that will qualify as a service contract. As a result, we end up with the awkward namespace collision that microservices expose services – but aren’t services themselves in the sense of service as a contracted interface.

But that distinction is neither here nor there. Maybe it’s time to update our notion of service to include units of execution. Especially if we’re using containers.

Microservice Architecture as Container-Oriented Architecture

It’s no coincidence, of course, that the definition of microservice makes them particularly well-suited for containers. And while you could certainly implement microservices without containers and vice-versa, there’s no question that the cool kids are combining these two approaches.

If you’ve been following the activity in the container world, you’ll have noticed that quite a bit of thought has been going into the question as to what container-oriented architecture best practices might be. Docker in particular is blazing this trail – but the work isn’t nearly ready for prime time.

Even in its formative state, however, container-oriented architecture doesn’t look much like SOA – done right or not. And yet, the questions of whether microservice architecture and container-oriented architecture will end up being the same thing – or even whether they should be the same thing – still remain to be answered.

Regardless of which side you fall on these questions, there are aspects of container-oriented architecture that weren’t part of the SOA story – or at least, the first-generation SOA story: cloud architecture best practices.

What cloud computing brought to the SOA table are the principles of horizontal scalability and elasticity, automated recovery from failure, eventually consistent data (or more precisely, tunable data consistency), and a handful of other now-familiar architectural principles.

And in fact, these cloud principles complement next-generation SOA, just as they form the basis of container-oriented architecture. And since microservices are container-friendly by design, our argument of architects might argue that microservices architecture is SOA plus cloud architecture done right.

Service Composition: The Missing Piece of the Puzzle

One important aspect of the SOA story is missing from this discussion, however: service composition. Central to first-generation SOA was the goal of composing services in order to implement business processes – a goal that led to the BPEL standard for Web Service composition, a debacle that to this day remains notorious for its abject failure.

Bottom line: if you want to talk about SOA done wrong, look no further than how service compositions failed to implement business processes.

As we moved to second generation, REST-based SOA, the service composition story takes an interesting turn, as REST does have an angle here: hypermedia. Roy Fielding’s original vision for REST was as an architectural style for building hypermedia systems – and lo and behold, what is a hypermedia system but an executable composition of RESTful services?

Still with me? No? Well, you’re not alone. Few people understood all this gobbledygook about hypermedia, in particular, REST’s hypermedia constraint – you know, hypermedia as the engine of application state? – so they decided to punt on the whole shebang. REST in practice became little more than an API style, which it remains to this day.

So now we’re discussing microservices architecture – which means we have to ask how best to compose microservices. The jury is still out on this question, but there’s one thing I can say about microservice composition: it must be parsimonious and it must be cohesive.

And given that microservices have RESTful interfaces, the architectural approach for composing them that is both parsimonious and cohesive is to treat microservice compositions as hypermedia systems.

Mark my words: microservices architecture will never be SOA done right unless it means building hypermedia systems of microservices. You heard it here first, folks.

The Intellyx Take: SOA Done Right

SOA has always been a rather loose collection of architectural best practices. And you know what makes a practice a best practice? You try a bunch of things, and the one that sucks the least is the best practice. At least, until a better one comes along.

Now that SOA has a few decades under its belt, the loose collection of best practices we call SOA continues to mature, as new practices gradually supplant earlier contenders. In this bucket we’re now adding various microservices best practices and container best practices – both unquestionably in their “whatever sucks the least” phase.

And we’ve also added cloud best practices and REST best practices to the mix – including the hypermedia best practices that have always been the raison d’être of REST. And to be sure, we have our tried and true SOA practices – not the ones that led us to failure, but the practices that through years of hard work and trial and error finally led us to successful implementations that supported our business agility drivers.

SOA done right, therefore, isn’t a fixed goal to aspire to. It’s a journey of architectural discovery, as we piece together the hard-fought lessons of enterprise system deployments, one practice at a time. And as long as we learn the lessons of the past, we will continue to make progress toward our ultimate business goals – sucking less as we go.

Intellyx advises companies on their digital transformation initiatives and helps vendors communicate their agility stories. At the time of writing, none of the organizations mentioned in this article are Intellyx customers. Image credit: Aussie~mobs.

4 Comments

  1. Mike Edwards says:

    What do “building hypermedia systems of microservices” and “REST best practices” mean in the context of microservices?

    • Jason Bloomberg says:

      I’m sure I’ll weigh in on these questions in a future newsletter. I’d also like to see what the broader microservices community comes up with as well. I get the sense that nobody has firm answers yet, especially if you’re looking for working deployments.

  2. Marcelo Carvalho Fernandes says:

    Hi Jason!
    I work with an ESB but since the beginning in 2008 we just build RESTful services (no SOAP). More recently we are applying on our ESB almost everything vendors now try to sell as “API Management” tools.

    I would like to know why the distinction of “first generation SOA” being the use of ESB and “second SOA generation” as being REST if you can do REST with ESB. Do you consider then as mutually exclusive?

    By the way, I came to this post after you commented a LinkedIn post of Software AG related to SOA and Microservices.

    Thanks in advance,

    Marcelo

    • Jason Bloomberg says:

      I characterized first and second generation SOA as ESB-centric and REST-based, but those characterizations represent general implementation patterns rather than specific requirements. You could certainly implement REST-based SOA with an ESB, and similarly, you could have RESTful interfaces and still have an architecture I’d characterize as first-generation.

      Here’s an article from 2011 where I explained more what I meant by REST-based SOA: http://jasonbloomberg.sys-con.com/node/1935038 . Note that in the intervening time, the world has moved on to microservices architecture, so even REST-based SOA is not fully current in terms of its practices.

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