Elixir on Heroku with Docker Containers

It is possible to deploy your Elixir application on Heroku using the Elixir Buildpack . However, you may want to deploy using Docker on Heroku instead. Perhaps your application has complex setup or configuration needs. Or perhaps you already have a Docker-ified application and you don’t want to have to do extra work to convert it to buildpacks and Procfiles.

Heroku supports Docker via the Container Registry and Runtime. Here’s the process of getting it set up:

Create a Heroku application with heroku create .
Set the Heroku stack to “container” heroku set:stack container. This enables the container functionality and ensures that Heroku doesn’t become confused if your project also contains other manifests (such as package.json or Gemfile).
Set up your Docker environment to talk to Heroku’s Docker registry instead of the default Docker registry: heroku container:login.
Build the image and push it to the Heroku registry: heroku container:push web.
Deploy it to your dynos: heroku container:release web.
Check your site and make sure everything works.
If your application does not boot and logs the error message Shall I install Hex? (if running non-interactively, use "mix local.hex --force") [Yn] ** (Mix) Could not find an SCM for dependency :phoenix from .Mixfile, you may have to make a small change to your Dockerfile.

Add ENV MIX_HOME=/opt/mix before you install hex & rebar in your Dockerfile. The reason this is needed from what I can gather is that Heroku’s Docker execution environment is different from your local development environment.

For reference, here’s my full Dockerfile for my Phoenix application:



        1
        FROM elixir:1.8.0-alpine
      

        2
        
      

        3
        RUN apk add make gcc libc-dev
      

        4
        
      

        5
        ENV CC=gcc
      

        6
        ENV MIX_HOME=/opt/mix
      

        7
        
      

        8
        RUN mix local.hex --force \\
      

        9
          && mix local.rebar --force
      

        10
        
      

        11
        WORKDIR /root/app
      

        12
        
      

        13
        ADD ./ /root/app/
      

        14
        
      

        15
        EXPOSE 4000
      

        16
        
      

        17
        ARG MIX_ENV=prod
      

        18
        RUN echo ${MIX_ENV}
      

        19
        ENV MIX_ENV=$MIX_ENV
      

        20
        ENV PORT=4000
      

        21
        
      

        22
        RUN mix deps.get
      

        23
        RUN mix deps.compile
      

        24
        RUN MAKE=cmake mix compile
      

        25
        RUN mix phx.digest
      

        26
        
      

        27
        CMD ["mix", "phx.server"]

1	FROM elixir:1.8.0-alpine
2
3	RUN apk add make gcc libc-dev
4
5	ENV CC=gcc
6	ENV MIX_HOME=/opt/mix
7
8	RUN mix local.hex --force \\
9	&& mix local.rebar --force
10
11	WORKDIR /root/app
12
13	ADD ./ /root/app/
14
15	EXPOSE 4000
16
17	ARG MIX_ENV=prod
18	RUN echo ${MIX_ENV}
19	ENV MIX_ENV=$MIX_ENV
20	ENV PORT=4000
21
22	RUN mix deps.get
23	RUN mix deps.compile
24	RUN MAKE=cmake mix compile
25	RUN mix phx.digest
26
27	CMD ["mix", "phx.server"]