Front end development with docker

This was originally published on 8 Feb 2015 in my old blog.

A more recent example of this idea based on Docker for Mac can be found at

Recently I decided to figure out how Docker would fit into my workflow as a front end developer.

I've always loved the idea of having easily reproducible development environments and keeping them as close to production as possible, and have tried to achieve that for things that I've worked with recently. Given that this is one of the main aspects of Docker, I've naturally been interested in it since it came along.

At my current workplace we use a Vagrant VM with a shell script for provisioning (soon to be converted into Chef to make it close to the production deployment procedure), which works quite well. Everyone gets the same environment, when something gets screwed up you can destroy the whole thing and recreate it from scratch, and when something needs to be updated it's easy for everyone to do it.

However, our infrastructure has grown over time, and with the proliferation of microservices, the idea of rebuilding the whole thing because of a minor update seems a bit wasteful. Which is why we've been thinking that containerisation might be something we want to seriously consider.

While I've read a lot about Docker and experimented with it before, I had never really tried to actually setup a project with it, and as part of a new pet project I decided to give it a try and see how it would fit in with a front end development workflow, which potentially will also be useful knowledge if we decide to go the container way at my workplace.

I won't explain much about what Docker is and how it works, so if you'd like to learn more about that, have a look at their User Guide and interactive tutorial.

Also, given that I'm fairly inexperienced with Docker and while I've done a lot of reading and research, there might be obvious and glaring mistakes on my approach, or things that could be done better, so please do let me know if there is any way I could improve upon this approach.

The App

While the workflow I'm about to describe here should work for any front end development setup, I think it's a good idea to first explain what I'm trying to build and how it'll fit into a container setup.

First of all, what's a common front end development setup nowadays? There's all sorts of build systems which can be used to run your code in development and build it for production, but most of these follow the principle of having some kind of file watcher for development, recompiling JS, CSS and whatever else necessary, and then having a separate task for building a production ready version of those assets.

Separately, there is some server (some times part of the developer build chain, some times separate) that serves those files for development.

In this specific case I have a very simple Node.js app, which exists solely for the purpose of doing the "OAuth dance" with an external service, so that users can login with their personal accounts on that 3rd party service and then get back to the app.

Other than that, all the app does is serve a client side only single page app, which I'm serving from the Node.js app directly for simplicity.

To be fair, using containers or even a VM here is kind of overkill, but this is mostly for experimentation and demonstration purposes, and this approach would fit well into any kind of infrastructure.

So anyway, that's one container right there, for the Node.js app. And that's pretty much the only thing I want to ship and run in production.

Now, I could be completely lazy and just add all my development tools to that container and be done with it. I could then run Docker in interactive mode, run a file watcher with my build chain in there and that would work.

And pretty much all the articles I've seen so far where people use Docker for front end development follow that pattern. Given that one of the principles of using containers is keeping them as lightweight and simple as possible, that approach goes a bit against that point.

So I'd like to avoid shipping anything that isn't necessary which means I want to keep the front end build chain outside of that container. In fact, that container shouldn't even have to worry with having to build those assets for production.

The Setup

The way building new containers with Dockerfiles works is usually something like this:

  • Choose a base image
  • Define the work directory where things will run
  • Tell Docker how to copy your app context (which is the directory where your Dockerfile lives) into the container
  • Expose ports
  • Define the commands which install whatever you want to run in the container
  • Define the entrypoint command, which is usually the main process you want to run in the container

Alternatively or in addition, you can setup data volumes. These can come from other containers, or from your local filesystem. The former is a way of sharing data across containers, where as the latter, while it can serve the same purpose, seems to be more often used for development purposes.

A thing we need to understand is that when in a Dockerfile we define that some data will be copied into the container, that only happens at build time. If you want to detect file changes while the container is running, you need to use a data volume. It's essentially like a shared directory in a VM. If you're using boot2docker on a Mac it's actually a shared directory on a VM, because that's what boot2docker is (and that poses a problem which I'll get to further ahead).

With all this in mind, there were a few limitations that made this development setup not so obvious:

  • You can only have one Dockerfile per directory
  • You can only copy files into the container which are already inside the current context
  • You can only mount volumes with absolute paths

After a bunch of fiddling around I came up with the following setup, which is actually rather simple (but maybe a bit hacky):

|-- Dockerfile
|-- app
|   |-- Dockerfile
|   |-- Makefile
|   |-- app.js
|   |-- build
|   |   |-- ...
|   |-- package.json
|   |-- public
|       |-- ...
|-- fig.yml
  • The top level Dockerfile defines the development toolchain container
  • app/Dockerfile defines the server container, and it's what we want to ship to production
  • There's a fig.yml which we use for Fig to start everything up together

Let's start with the server Dockerfile, which lives inside the app directory:

FROM nodesource/node:trusty
COPY . /src
RUN npm install --prod
CMD /usr/bin/node app.js

That's fairly simple. It uses a base image with Node.js installed, copies the current context into the /src directory, installs dependencies and starts the server.

Note how we're using the --prod flag for npm install, which ensures we're not installing anything necessary for development.

A thing to notice is that app.js serves the index.html file and everything under build as static files.

Now let's have a look at the top level file for the build toolchain:

FROM nodesource/node:trusty
COPY app/ /src
RUN npm install -g watchy
RUN npm install

We're using the same base image, copying the same data (which in this case is inside the app directory), installing different dependencies (without the --prod flag npm installs devDependencies by default). We're not running any command as an entrypoint here, because we want to use this container not just for our development setup, but also to build the assets for production. More on that ahead.

Now, remember how I mentioned earlier that we want to use volumes in order to check what files changed and reload the code appropriately?

We could've specified the volumes in the Dockerfile, but because they're not necessary for production we want to keep them out of there.

A thing that got me is that if you use volumes and have a RUN command in your Dockerfile, those RUN commands can't really operate on data that comes from the volumes, because they will not be available at that moment. This is why we need to make sure that we still use the COPY command to get the necessary data there at build time.

So how do we specify the volumes? Remember that fig.yml file up there? We're going to use fig to help us start all of our containers at once, but also to setup our volumes:

  build: app/
  - "6001:6001"
  - app/:/src
  build: .
  - app/:/src
  entrypoint: ["/usr/bin/watchy", "-w", "public/javascripts", "--", "/usr/bin/make", "all"]

Here we're also specifying the command which runs the file watcher, because we only want to use fig for development.

You start everything with fig up and your development environment is up and running.

Production deployments

I didn't spend a lot of time trying to figure this one out, but the idea is also simple. We should have a task in that Makefile that builds assets for production, which we can run in the context of our development container, such as:

docker run -ti myproject_projectclient make production

Then, if you rebuild your production container that data should be ready for it to copied into it's own context.

The caveat(s)

Now, this is all very nice and adaptable to different setups. It's just one extra container which you use for managing your front end development toolchain.

However, at the moment there is one major issue with this setup, which only applies if you're running a Mac with boot2docker but it's nevertheless a show stopper.

If you ever did front end development with Vagrant/Virtualbox and shared directories, you've certainly come across the issue with file change detection being too slow if you're using the default file sharing mechanism in Virtualbox. The way to usually fix this is to use NFS, and maybe tweak a few options in order to speed things up.

It works fine, we use it on our development VM at work, but at the moment it's not possible to change that with boot2docker, or at least not trivial. Here's a whole thread on that issue where some people have managed to get it working, but it doesn't seem like there is yet a straightforward out of the box solution for anyone.

Apart from that, there's a bunch of other things that could've been more straightforward. While I don't particularly appreciate the overly agressive tone of this article and a lot of the issues pointed out don't apply to this use case, I particulary agree with the part about the Dockerfile. It feels like this should and could be simpler, specially if the idea from the outset is to have many small containers for each service.

In conclusion

This was an interesting experiment but until a way to fix the NFS file share issue comes along, I probably won't be using Docker for any kind of front end development.

However, this is what I see as possibly the best approach to setup a Docker development environment for the front end, in a way that lets you take advantage of Docker and easily integrate with existing, more complex infrastructures.