Merge Dockerfile and add CI

.github/workflows/ci.yml

@@ -0,0 +1,52 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  build-and-test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Build base stage
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: docker/Dockerfile
+          target: base
+          load: true
+          tags: elixir-docker-template:base
+
+      - name: Build dev stage
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: docker/Dockerfile
+          target: dev
+          load: true
+          tags: elixir-docker-template:dev
+
+      - name: Build prod stage
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: docker/Dockerfile
+          target: prod
+          load: true
+          tags: elixir-docker-template:prod
+
+      - name: Validate compose
+        run: docker compose config --quiet
+
+      - name: Run Hadolint
+        uses: hadolint/hadolint-action@v3.1.0
+        with:
+          dockerfile: docker/Dockerfile
+          ignore: DL3008

.gitignore

@@ -1 +0,0 @@
-mutagen.yml.lock

.hadolint.yaml

@@ -0,0 +1,2 @@
+ignored:
+  - DL3008

README.md

@@ -20,6 +20,7 @@ help to miss some hurdles.
 
 - Docker based environment for Elixir / Erlang
 - `justfile` for easier handling of the stack
+- Multi-stage Dockerfile for dev and production builds
 
 ## Prerequisites
 
@@ -28,6 +29,65 @@ You need to have the following installed:
 - [Docker](https://docker.io) for running the code
 - [Just](https://just.systems) for running commands
 
+## Docker Build
+
+The template uses a single `docker/Dockerfile` with multiple build stages:
+
+| Stage | Purpose |
+|-------|---------|
+| `base` | Base image with essential tools |
+| `dev` | Development environment (default) |
+| `prod` | Production build environment |
+
+### Build Commands
+
+```bash
+# Development (via compose)
+just start
+
+# Production
+docker build --target prod -t myapp:prod .
+```
+
+The versions are defined in the `FROM` statement in the base stage (currently Elixir 1.19.5, Erlang 28.3, Debian trixie).
+
+### Optimized Production Build
+
+For a smaller production image, you can use a two-stage build pattern. Create a separate `Dockerfile.prod` based on the template's commented sections:
+
+```dockerfile
+# Stage 1: Builder
+FROM docker.io/hexpm/elixir:1.19.5-erlang-28.3-debian-trixie-20260202-slim AS builder
+
+WORKDIR /app
+RUN mix local.hex --force && mix local.rebar --force
+
+COPY mix.exs mix.lock ./
+RUN mix deps.get --only prod
+RUN mix deps.compile
+
+COPY config/ config/
+COPY lib/ lib/
+COPY priv/ priv/
+RUN mix compile
+
+COPY rel/ rel/
+RUN mix release
+
+# Stage 2: Runtime
+FROM debian:trixie-20260202-slim
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+  libstdc++6 openssl libncurses6 locales ca-certificates \
+  && rm -rf /var/lib/apt/lists/*
+
+ENV LANG=en_US.UTF-8
+WORKDIR /app
+
+COPY --from=builder /app/_build/prod/rel/your_app ./
+CMD ["./bin/server"]
+```
+
 ## Usage
 
 To use the template either download the files and augment an existing project

compose.yml

@@ -3,7 +3,8 @@ services:
     init: true
     build:
       context: .
-      dockerfile: docker/Dockerfile.dev
+      dockerfile: docker/Dockerfile
+      target: dev
     stdin_open: true
     tty: true
     volumes:
@@ -34,9 +35,8 @@ services:
 #      - default
 
 volumes:
-  #  postgres-data:
+  # postgres-data:
   app:
-    # The lines below need to be removed when using mutagen
     driver: local
     driver_opts:
       o: bind

docker/Dockerfile

@@ -0,0 +1,92 @@
+# ============================================
+# Multi-stage Dockerfile for Elixir development
+#
+# Build stages:
+#   --target base : Base image with essential tools
+#   --target dev  : Development environment (default)
+#   --target prod : Production build environment
+#
+# Examples:
+#   docker build --target dev -t myapp:dev .
+#   docker build --target prod -t myapp:prod .
+# ============================================
+
+# ============================================
+# Stage 1: Base
+# Single source of truth for versions
+# ============================================
+FROM docker.io/hexpm/elixir:1.19.5-erlang-28.3-debian-trixie-20260202-slim AS base
+
+RUN apt-get update -qq && \
+  apt-get install -y --no-install-recommends \
+  build-essential git curl make \
+  # When using Postgres uncomment the following line
+  # libpq-dev postgresql-client\
+  && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+RUN mix local.hex --force && mix local.rebar --force
+
+# ============================================
+# Stage 2: Dev
+# Development environment with interactive shell
+# ============================================
+FROM base AS dev
+
+RUN apt-get update -qq && \
+  apt-get install -y --no-install-recommends \
+  erlang-crypto inotify-tools \
+  && rm -rf /var/lib/apt/lists/*
+
+COPY docker/app/run.sh /run.sh
+RUN chmod +x /run.sh
+
+CMD ["/run.sh"]
+
+# ============================================
+# Stage 3: Prod
+# Production build environment
+# ============================================
+FROM base AS prod
+
+RUN apt-get update && \
+  apt-get install -y --no-install-recommends \
+  libstdc++6 openssl libncurses6 locales ca-certificates \
+  && rm -rf /var/lib/apt/lists/*
+
+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
+ENV MIX_ENV=prod
+
+# To use for production:
+# 1. Uncomment to install dependencies:
+# COPY mix.exs mix.lock ./
+# RUN mix deps.get --only prod
+# RUN mix deps.compile
+
+# 2. Uncomment if your project has a config directory:
+# COPY config/config.exs config/prod.exs config/
+
+# 3. Uncomment if your project has assets:
+# RUN mix assets.setup
+# COPY assets assets
+# COPY priv priv
+# COPY lib lib
+
+# 4. Uncomment to compile the application:
+# RUN mix compile
+
+# 5. Uncomment to build assets for production:
+# RUN mix assets.deploy
+
+# 6. Uncomment to build the release:
+# COPY rel rel
+# RUN mix release
+
+# 7. Update CMD to match your app:
+# CMD ["/app/bin/server"]