Dry

Without a doubt, Microservices as an architecture has grasped the imagination of modern development like no other.

We’ve found that, contrary to what many will tell you, it defies tight definition. Specifying how microservices should interact with each other, how they should store and master data, and how they should be deployed is great for a conference talk, but the style has been adopted too broadly now to be prescriptively tied down by anyone. Opinions abound, and yet you will find no consensus in what microservices actually are beyond the use of some form of effective isolation, usually network based.

My good friend Peter Ledbrook has been pondering the question how can we share code between microservices

This is something we’ve had the opportunity to experiment with, on new projects and also longer running systems. This has given us some insight, which I’m happy to share here.

The process for building a new microservice is pretty well established by now.

• Define the service contract
• Expose on a network (somehow, http, messaging, or maybe https://muoncore.io[Muon])
• Profit?

…​

The Original DRY, WET and Slogan Based Development

Hopefully, you now understand some of my pain when I’m arguing against DRY, and arguing against deep abstractions. The original definition of DRY though, Single Source of Truth etc, that’s ok right? I mean, WET (Write Everything Twice etc) just sounds so bad, and it’s the opposite of DRY, right?

Well …​ no, not really. This is development by slogan, pure and simple. Luke is right to fear this, it leads to dogma and dogmatic position taking and so to endless, needless, debate and argument over developer practices.

Don’t Repeat Anything == The Tower of Coupling

Copy and Paste, it’s bad. We have this drilled into us as received knowledge. We must build abstractions to avoid copying code, or concepts that seem similar, at all costs. We must do this, or we are bad developers and we’ve built a WET (Write Everything Twice .. etc) system, which isn’t DRY, so it’s bad.

I did a fun little talk a while ago that touched on this (seriously, go and do something a little silly every so often, it’s fun), and pointed to the problem that is inherent in applying DRY too broadly; Coupling.

I recently had a thought provoking exchange on Twitter with Luke Daley who is a Gradle developer, creator of the Ratpack web framework and all around awesome fellow.

We were briefly discussing DRY, aka Don’t Repeat Yourself, that great maxim of modern software development. My opening gambit was that ‘DRY totally sucks’ (because well, Twitter..). Luke picked me up on this, asking for a more nuanced view, more depth. His entirely reasonable request, to not ‘propagate software development by slogan’, which I’ve unashamedly stolen as my title is one we should all pay attention to.

No programmer likes to plan for their work to be taken offline and shutdown, but part of good antifragile thinking is allowing things that aren’t successful, to end. Applying that to Microservices, one of the natural parts of that architectural style is creating and destroying instances of a service. As part of the lifecycle of services, you sometimes have to create different versions of a service, and so manage the retiring of a previous version (although we try to avoid versioning where possible).