I’ve been giving talks on what are now called microservices for the past two years. The big idea is that in some situations rather than building a monolithic application (e.g. application = one huge WAR file) you should apply the Scale Cube (specifically y-axis splits aka. functional decomposition) and design your application as a collection of independently deployable services.
I have often introduced the idea as “SOA light” since you are building a service-oriented architecture. The trouble with the term SOA, however, is that it is associated with a lot of baggage: SOAP, ESBs, heavyweight ceremony, etc. Instead, I’ve talked about “Decomposing the monolith” or “Decomposing the WAR”. I’ve also used the term modular, polyglot architecture but that’s a bit of a mouthful.
At Oredev 2012, I encountered Fred George who was giving a talk on what he called microservices, which was a variant of what I had been talking about. What was especially intriguing about his approach was about how it pushed things to the extreme with a very heavy emphasis on very small services. The term microservices along with the idea of tiny 100 LOC services has got a fair amount of buzz recently. Martin fowler blogged about microservices and there has been some discussion on twitter.
On the one hand, I like the term microservices. It’s short and it catchy. The problem, however, is that it IMHO places excessive emphasis on smallness. After all, as I described at the start of this post the big idea is to break up the otherwise monolithic application into smaller, more manageable services by applying function decomposition. Some of those services can be just a few lines of code. For example, in one of my sample applications I have a 12 line Sinatra service that responds to SMS messages. While some services can be this small, others will need to be a lot larger. And that’s just fine. It all depends. Partitioning an application is a tricky design problem that has to balance a large number of constraints. To paraphrase Einstein, “Services should be made as small as possible, but no smaller.”