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Put your Elixir app production release inside minimal docker image


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mix docker

🚨🚨 This project is now obsolete and abandoned! 🚨🚨

With docker multi-stage builds you can simply use:

# Dockerfile
FROM elixir:1.6.5-alpine as build

# install build dependencies
RUN apk add --update git

# prepare build dir
RUN mkdir /app

# install hex + rebar
RUN mix local.hex --force && \
    mix local.rebar --force

# set build ENV

# install mix dependencies
COPY mix.exs mix.lock ./
COPY config ./
COPY deps ./
RUN mix deps.compile

# build release
COPY . .
RUN mix release --no-tar --verbose

# prepare release image
FROM alpine:3.6
RUN apk add --update bash openssl

RUN mkdir /app && chown -R nobody: /app
USER nobody

COPY --from=build /app/_build/prod/rel/myapp ./


ENTRYPOINT ["/app/bin/myapp"]

and standard docker build.


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, "~> 0.5.0"}]
  1. Configure Docker image name
# config/config.exs
config :mix_docker, image: "recruitee/hello"
  1. Run mix docker.init to init distillery release configuration

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



Build a release

Run mix 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 configure the image tag?

By default, the image tag uses the following format: {mix-version}.{git-count}-{git-sha} You can provide your own tag template in config/prod.exs like this:

# config/config.exs
config :mix_docker,
  tag: "dev_{mix-version}_{git-sha}"

Additionally, you can pass the tag as an argument to mix docker.publish and mix docker.shipit:

mix docker.publish --tag "{mix-version}-{git-branch}"

See below for a list of possible variables

Variable Description
{mix-version} Current project version from mix.exs
{rel-version} Default distillery release version
{git-sha} Git commit SHA (10 characters)
{git-shaN} Git commit SHA (N characters)
{git-count} Git commit count
{git-branch} Git branch

What version of Erlang/Elixir is installed by default?

The default dockerfiles are based on bitwalker/alpine-erlang and elixir installed from apk repository

The following table summarizes the default versions:

mix_docker version alpine erlang elixir
up to 0.3.2 3.4 18.3 elixir@edge at the time of build
0.4.0 3.5 19.2 elixir@edge=1.4.1-r0
0.4.1 3.5 19.2 elixir@edge=1.4.2-r0

Please note that you can use any version you want by customizing your dockerfiles. See mix docker.customize for reference.

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 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_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 an Umbrella app?

The default build Dockerfile does not handle the installation of umbrella app deps, so you will need to modify it to match the structure of your project.

Run mix docker.customize and then edit to copy across each of your umbrella's applications.

COPY mix.exs mix.lock ./

RUN mkdir -p apps/my_first_app/config
COPY apps/my_first_app/mix.exs apps/my_first_app/
COPY apps/my_first_app/config/* apps/my_first_app/config/

RUN mkdir -p apps/my_second_app/config
COPY apps/my_second_app/mix.exs apps/my_second_app/
COPY apps/my_second_app/config/* apps/my_second_app/config/

# etc.

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 as follows (add nodejs and python):

# Install Elixir and basic build dependencies
    echo "@edge" >> /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.