Example of Dockerfile for an Elixir application

elixir-node.dockerfile

FROM elixir:1.12-alpine AS builder

ARG BUILD_ENV=prod
ARG BUILD_REL=my_app

# Install system dependencies
RUN mix local.hex --force
RUN mix local.rebar --force

# Add sources
ADD . /workspace/
WORKDIR /workspace

ENV MIX_ENV=${BUILD_ENV}

# Fetch dependencies
RUN mix deps.get

# Build project
RUN mix compile

# Run test-suite
RUN mix test --cover

# Build release
RUN mix release ${BUILD_REL}

FROM alpine:latest AS runner

ARG BUILD_ENV=prod
ARG BUILD_REL=my_app

# Install system dependencies
RUN apk add --no-cache openssl ncurses-libs libgcc libstdc++

# Install release
COPY --from=builder /workspace/_build/${BUILD_ENV}/rel/${BUILD_REL} /opt/myapp

## Configure environment

# We want a FQDN in the nodename
ENV RELEASE_DISTRIBUTION="name"

# This value should be overriden at runtime
ENV RELEASE_IP="127.0.0.1"

# This will be the basename of our node
ENV RELEASE_NAME="${BUILD_REL}"

# This will be the full nodename
ENV RELEASE_NODE="${RELEASE_NAME}@${RELEASE_IP}"

# If empty, the default cookie generated by `mix release` will be used
# OVERRIDE IT!!
ENV RELEASE_COOKIE=""

ENTRYPOINT ["/opt/myapp/bin/${BUILD_REL}"]
CMD ["start"]

The launcher.sh script:

#!/bin/sh

set -e

DEFAULT_COOKIE="$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 128 | head -n 1)"
export RELEASE_COOKIE="${RELEASE_COOKIE:-"$DEFAULT_COOKIE"}"
export RELEASE_NODE_IP="${RELEASE_NODE_IP:-"127.0.0.1"}"

export RELEASE_DISTRIBUTION="name"
export RELEASE_NODE="${RELEASE_NAME}@${RELEASE_NODE_IP}"

exec /opt/myapp/bin/${RELEASE_NAME} $@

The .dockerignore:

# The directory Mix will write compiled artifacts to.
/_build/

# If you run "mix test --cover", coverage assets end up here.
/cover/

# The directory Mix downloads your dependencies sources to.
/deps/

# Where third-party dependencies like ExDoc output generated docs.
/doc/

# Ignore .fetch files in case you like to edit your project deps locally.
/.fetch

# If the VM crashes, it generates a dump, let's ignore it too.
erl_crash.dump

# Also ignore archive artifacts (built via "mix archive.build").
*.ez

# Ignore package tarball (built via "mix hex.build").
myapp-*.tar

# Temporary files for e.g. tests
/tmp

# Dockerfiles
/docker/

# some more files depending on the project...