The Microservices train is leaving the station baby and everyone is getting on board. Lots of folks have written about Microservices and their benefits but a recent project experience has left me more interested in when you should use the approach.

Here are two posts which jibe with some of what I’ve recently felt.

Eric Lindvall of Papertrail:

When you’re starting out, and when you’re small, the speed at which you can make changes and improvements makes all the difference in the world. Having a bunch of separate services with interfaces and contracts just means that you have to make the same change in more places and have to do busywork to share code.

What can you do to reduce the friction required to push out that new feature or fix that bug? How can you reduce the number of steps that it takes to get a change into the hands of your users? Having code in a single repository, using an established web framework like Rails or Django can help a lot in reducing those steps. Don’t be scared of monolithic web apps when you’re small. Being small can be an advantage. Use it.

Adrian Cockcroft ex. Netflix:

I joined Netflix in ‘07 and the architecture then was a monolithic development; a two week Agile sort of train model sprint if you like. And every two weeks the code would be given to QA for a few days and then Operations would try to make it work, and eventually … every two weeks we would do that again; go through that cycle. And that worked fine for small teams and that is the way most people should start off. I mean if you’ve got a hand full of people who are building a monolith, you don’t know what you are doing, you are trying to find your business model, and so it’s the ability to just keep rapidly throwing code at the customer base is really important.

Once you figure out how… Once you’ve got a large number of customers, and assuming that you are building some Web-based, SasS-based kind of service, you start to get a bigger team, you start to need more availability.

Large projects with long-term timelines seem like good candidates for using the Microservices approach¹.

On the other hand, new products or services may not be the right situation to immediately dive in with a Microservices approach. It’s likely that the idea itself is being fleshed out and investing anywhere outside of that core goal is ultimately waste. Carving process boundaries throughout your domain in this early turbulent stage is going to slow you down when you inevitably need to move them.

Pushing infrastructure style functionality—such as logging or email delivery—out into services makes sense, but waiting to see how things develop seems worthwhile when it comes to the core domain. Initially focussing on understanding the domain and investing in getting changes out to production as quickly as possible is likely more important then developing loads of cross-process plumbing.

A monolithic application isn’t such a bad place to start. The trick, as always, is to know when to change that plan.