Why?

During the last six months, I started using Docker to host my (mostly RoR) apps in development. I just wanted to try and learn something new, I ended up with a new approach to my everyday tasks.

You can find everything you need to install Docker and Compose in the official documentation. There is even a guide to bootstrap a RoR app with Docker here.

I found a number of example Dockerfiles (and docker-compose files) around but mainly focused on deploy. They did not work either for development, for me, or at all sometimes.

So, I decided to write down the solutions I came up with as for now, in case anyone was struggling as I was :)

TL;DR
You can find a list of Docker with Compose for RoR files examples here.

Yes, but why should I dockerize my app?

The main thing I love is not having to configure (almost) anything on the hosting machine, either in development or production.

Working on Linux I like to change distro every now and then. Every time I did I needed to install and configure many packages, in many versions. Yes I could script most of that, but I discovered I like to have a clean machine, with just the strict necessary for generic activities.

Now I don’t need to install/reinstall every version of ruby I use in every project I own, nor I do have to install every library I did in the past, just to pick up again an old project.

Everything is as simple as typing sudo docker-compose up (actually I made an abbr for that. Did I talk about fish yet?)

Anything else?

You can find a load of articles talking about the pros and cons of containerizing your application, both on a technical and a practical level.

Something that really made the difference for me was having the same environment in development and production. More than occasionally I found my apps working on my laptop and breaking in some way on the server. Not anymore, containers configuration is the same on any machine I install my apps on.

As I said before, nothing to configure, you pull the images and are ready to go!

Another perk I enjoy is the possibility to try any kind of software upgrade in the container, without risk. If something breaks, you just go back to the previous version of your docker files.

What about the downsides?

The configuration of Docker/Compose can be a pain, particularly if you are a beginner. But once it’s done you can spawn your app on any machine (with Docker installed) in no time.

Sometimes Rails basic configuration is tougher using Docker. Running system tests inside a container was not the easiest thing to implement.

As some problems are solved by containerizing applications, new ones are created. For instance, bundle breaks more easily when switching between branches and if you don’t know how to fix it can be frustrating. This sort of problems can be generally avoided, if you are willing to get used to slightly different patterns while developing.

So, I’m a Ruby on Rails developer wishing to try Docker, what should I do?

Official guides are very detailed and always up to date, i recommend to carefully read and follow every installation step for your OS. I really suggest installing Compose shell completions also.

Dockerfile and Compose references were very useful for me. Every command and option is explained clearly and in depth.

After that, you just have to add a couple of files to your project to configure its containers.


Next step: Adding the Dockerfile