Dockerfile

# Find eligible builder and runner images on Docker Hub. We use Ubuntu/Debian instead of
# Alpine to avoid DNS resolution issues in production.
#
# https://hub.docker.com/r/hexpm/elixir/tags?page=1&name=ubuntu
# https://hub.docker.com/_/ubuntu?tab=tags
#
#
# This file is based on these images:
#
#   - https://hub.docker.com/r/hexpm/elixir/tags - for the build image
#   - https://hub.docker.com/_/debian?tab=tags&page=1&name=bullseye-20220801-slim - for the release image
#   - https://pkgs.org/ - resource for finding needed packages
#   - Ex: hexpm/elixir:1.13.4-erlang-25.0.4-debian-bullseye-20220801-slim
#
ARG ELIXIR_VERSION=1.18.4
ARG OTP_VERSION=27.3.4.1
ARG DEBIAN_VERSION=bookworm-20250630-slim

ARG BUILDER_IMAGE="hexpm/elixir:${ELIXIR_VERSION}-erlang-${OTP_VERSION}-debian-${DEBIAN_VERSION}"
ARG RUNNER_IMAGE="debian:${DEBIAN_VERSION}"

FROM ${BUILDER_IMAGE} AS builder

ARG DEPLOY_DOMAIN="https://elixirschool.com"

# install build dependencies
RUN rm -f /etc/apt/apt.conf.d/docker-clean

RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
    --mount=type=cache,target=/var/lib/apt,sharing=locked \
    apt-get update -y && \
    apt-get install -y build-essential git npm --fix-missing --no-install-recommends && \
    apt-get clean && \
    rm -f /var/lib/apt/lists/*_*

# prepare build dir
WORKDIR /app

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

# set build ENV
ENV MIX_ENV="prod"

# install mix dependencies
COPY mix.exs mix.lock ./
RUN mix deps.get --only $MIX_ENV
RUN mkdir config

# copy compile-time config files before we compile dependencies
# to ensure any relevant config change will trigger the dependencies
# to be re-compiled.
COPY config/config.exs config/lessons.exs config/redirects.exs config/${MIX_ENV}.exs config/
RUN mix deps.compile

COPY priv priv

COPY lib lib

COPY assets assets

COPY Makefile Makefile

# install npm dependencies
RUN cd assets && npm ci

# install content from remote repository
RUN make content

# generate rss and sitemap static files
RUN mix school_house.gen.rss ${DEPLOY_DOMAIN}
RUN mix school_house.gen.sitemap ${DEPLOY_DOMAIN}

# compile assets
RUN mix assets.deploy

# Compile the release
RUN mix compile

# Changes to config/runtime.exs don't require recompiling the code
COPY config/runtime.exs config/

COPY rel rel
RUN mix release

# start a new build stage so that the final image will only contain
# the compiled release and other runtime necessities
FROM ${RUNNER_IMAGE}

RUN rm -f /etc/apt/apt.conf.d/docker-clean

RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
    --mount=type=cache,target=/var/lib/apt,sharing=locked \
    apt-get update -y && \
    apt-get install -y libstdc++6 openssl libncurses5 locales ca-certificates tini && \
    apt-get clean && \
    rm -f /var/lib/apt/lists/*_*

# Set the locale
RUN sed -i '/en_US.UTF-8/s/^# //g' /etc/locale.gen && locale-gen

ENV LANG=en_US.UTF-8
ENV LANGUAGE=en_US:en
ENV LC_ALL=en_US.UTF-8

WORKDIR "/app"
RUN chown nobody /app

# set runner ENV
ENV MIX_ENV="prod"

# Appended by flyctl
ENV ECTO_IPV6=true
ENV ERL_AFLAGS="-proto_dist inet6_tcp"

# Allow any release script to be ran without prefix
ENV PATH="$PATH:/app/bin"

# Only copy the final release from the build stage
COPY --from=builder --chown=nobody:root /app/_build/${MIX_ENV}/rel/school_house ./
COPY --from=builder --chown=nobody:root /app/priv/static ./static

USER nobody

ENTRYPOINT ["tini", "--"]

CMD ["/app/bin/server"]