DevOps and Containers

“Works on my machine!”

We’ve all had that co-worker. I have had one at pretty much every company I’ve worked for. At several jobs, it devolved into a running joke.

There is a belief that containers alleviate this issue. And they may—or they may simply mask the issue. The choice is up to IT.

Inevitably, something that works on one machine and not another can be traced back to on-the-fly configuration changes. If “we use containers for DevOps” means that developers have full control of the container environment, then it must also mean that any configuration changes be codified into a documented container image that can be spun up repeatedly and even recreated in a Dockerfile if needed.

If, instead, it means that devs have a playground in containers and, once they get it going, they can chuck it into production—even if you don’t say it that bluntly—then you are making things worse with containers, not better. At least in the days of “works on my machine,” the issues had to be resolved because the only time you heard that phrase was if something didn’t work on the machines it needed to be deployed to!

As a developer, it is tempting in both container and virtual environments to upgrade a package or tweak a setting without documenting it. But a clean DevOps environment needs to be able to build the product from Dockerfiles, not from a pre-existing image. Yes, you can just clone the existing image, but then there is no documentation of what has actually been changed and it takes a lot more work for those following you and debugging future problems.

So take the time; keep an up-to-date Dockerfile (or whatever equivalent script is used to build your containers). It is not that significant an investment to stop for a minute, open a file and type a few lines. And it pays off in spades if, in the future, someone is trying to figure out what the heck is going on in there. Consider it self-documenting configuration. I’m not a fan of “self-documenting code,” but for config, it is pretty clear if you go, “Oh, we needed version 10.2, not version 10.1; let me update the init script.”

There are a fair number of shops out there that modify things running in production, and the world hasn’t ended yet—though that may well be how it happens. So, a good practice that will help those trying to follow behind you is clearly not a necessity. But each of us has gone back after a year and said, “Why did we do that this way?” which was (or wasn’t) then answered with, “Oh, here is exactly how the environment was configured.” But it might help answer the ‘why.’

Your apps are powering the world—or your specific apps are powering your little piece of it. And you’re kicking it just keeping them running. Now, go make them better! Consolidate changes, manage configuration through Dockerfiles, Ansible, init-scripts, whatever combination you use … And keep rocking.