Put your Elixir app production release inside minimal docker image
Latest commit d3f4a8e Feb 13, 2017 @teamon teamon v0.3.2


mix docker

Build Status

Put your Elixir app inside minimal Docker image. Based on alpine linux and distillery releases.


  1. Add mix_docker to your list of dependencies in mix.exs:

    def deps do
      [{:mix_docker, "~> 0.3.0"}]
  2. Configure Docker image name

    # config/config.exs
    config :mix_docker, image: "recruitee/hello"
  3. Run mix docker.init to init distillery release configuration

  4. Run mix docker.build & mix docker.release to build the image. See Usage for more.



Build a release

Run mix docker.build to build a release inside docker container

Create minimal run container

Run mix docker.release to put the release inside minimal docker image

Publish to docker registry

Run mix docker.publish to push newly created image to docker registry

All three in one pass

Run mix docker.shipit

Customize default Dockerfiles

Run mix docker.customize


How to configure my app?

Using ENV variables. The provided Docker images contain REPLACE_OS_VARS=true, so you can use "${VAR_NAME}" syntax in config/prod.exs like this:

config :hello, Hello.Endpoint,
  server: true,
  url: [host: "${DOMAIN}"]

config :hello, Hello.Mailer,
  adapter: Bamboo.MailgunAdapter,
  api_key: "${MAILGUN_API_KEY}"

How to attach to running app using remote_console?

The easiest way is to docker exec into running container and run the following command, where CID is the app container IO and hello is the name of your app.

docker exec -it CID /opt/app/bin/hello remote_console

How to install additional packages into build/release image?

First, run mix docker.customize to copy Dockerfile.build and Dockerfile.release into your project directory. Now you can add whatever you like using standard Dockerfile commands. Feel free to add some more apk packages or run some custom commands. TIP: To keep the build process efficient check whether a given package is required only for compilation (build) or runtime (release) or both.

How to move the Dockerfiles?

You can specify where to find the two Dockerfiles in the config.

# config/config.exs
config :mix_docker,
  dockerfile_build: "path/to/Dockerfile.build",
  dockerfile_release: "path/to/Dockerfile.release"

The path is relative to the project root, and the files must be located inside the root.

How to configure a Phoenix app?

To run a Phoenix app you'll need to install additional packages into the build image: run mix docker.customize.

Modify the apk --no-cache --update add command in the Dockerfile.build as follows (add nodejs and python):

# Install Elixir and basic build dependencies
    echo "@edge http://nl.alpinelinux.org/alpine/edge/community" >> /etc/apk/repositories && \
    apk update && \
    apk --no-cache --update add \
      git make g++ \
      nodejs python \
      elixir@edge && \
    rm -rf /var/cache/apk/*

Install nodejs dependencies and cache them by adding the following lines before the COPY command:

# Cache node deps
COPY package.json ./
RUN npm install

Build and digest static assets by adding the following lines after the COPY command:

RUN ./node_modules/brunch/bin/brunch b -p && \
    mix phoenix.digest

Add the following directories to .dockerignore:


Remove config/prod.secret.exs file and remove a reference to it from config/prod.exs. Configure your app's secrets directly in config/prod.exs using the environment variables.

Make sure to add server: true to your app's Endpoint config.

Build the images and run the release image normally.

Check out this post for detailed walkthrough of the Phoenix app configuration.