Update Dockerfile from LogRocket example

Dockerfile

@@ -1,37 +1,87 @@
+# Dockerfile is modified from the example given on the LogRocket blog
+# https://blog.logrocket.com/run-phoenix-application-docker/
+
 ARG ELIXIR_VERSION=1.17.3
 ARG OTP_VERSION=27.3.4.7
 ARG DEBIAN_VERSION=trixie-20260202-slim
+ARG BUILDER_IMAGE="hexpm/elixir:${ELIXIR_VERSION}-erlang-${OTP_VERSION}-debian-${DEBIAN_VERSION}"
+ARG RUNNER_IMAGE="debian:${DEBIAN_VERSION}"
 
-FROM "docker.io/hexpm/elixir:${ELIXIR_VERSION}-erlang-${OTP_VERSION}-debian-${DEBIAN_VERSION}"
+FROM ${BUILDER_IMAGE} as builder
 
 # Set the locale
 ENV LANG=en_US.UTF-8
 ENV LANGUAGE=en_US:en
 ENV LC_ALL=en_US.UTF-8
 
-# Install dependencies
-RUN apt-get update \
-    && apt-get install -y --no-install-recommends build-essential make gcc erlang-dev git autoconf automake libtool pkg-config \
-    && rm -rf /var/lib/apt/lists/*
+# Install dependencies, including C build tools for libsecp256k1
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends erlang-dev build-essential make gcc git autoconf automake libtool pkg-config && \
+    apt-get clean && \
+    rm -f /var/lib/apt/lists/*_*
 
 # Create a build directory and copy in the project files
 WORKDIR /app
-COPY . .
 
-# Compile the application
-RUN mix local.hex --force && mix local.rebar --force
-RUN mix deps.get --only prod
-RUN MIX_ENV=prod mix compile
+# Install Hex and Rebar
+RUN mix local.hex --force && \
+    mix local.rebar --force
+
+# Configure for prod build
+ENV MIX_ENV="prod"
 
-# Update the static Swagger documentation
-RUN MIX_ENV=prod mix phx.swagger.generate
+# Install Elixir application dependencies
+COPY mix.exs mix.lock ./
+RUN mix deps.get --only ${MIX_ENV}
 
-# Run as the isidore-dev user
-USER 1008
-RUN mix local.hex --force && mix local.rebar --force
+# Copy in config files before compiling dependencies.
+# This ensures config changes will force recompilation of dependencies.
+RUN mkdir config
+COPY config/config.exs config/${MIX_ENV}.exs config/
+
+# Compile Elixir application dependencies
+RUN mix deps.compile
+
+# Copy in static assets and source code
+# Note: Swagger docs must be generated before deployment; this image does not generate them.
+COPY priv priv
+COPY lib lib
+
+# Compile the app for production
+RUN mix compile
+
+# Copy in runtime config files.
+# Other config files are baked into the compilation, but runtime config is applied at runtime.
+COPY config/runtime.exs config/
+
+# Copy in any release files and create a release
+COPY rel rel
+RUN mix release
+
+# Lean runtime stage
+FROM ${RUNNER_IMAGE}
+RUN apt-get update && \
+    apt-get install -y libstdc++6 openssl libncurses5 locales && \
+    apt-get clean && \
+    rm -f /var/lib/apt/lists/*_*
+
+# Set the runtime 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
+
+# Transfer ownership of the app directory to the runtime user
+WORKDIR "/app"
+RUN chown 1008:1008 /app
 
-# Set environment variables for the application
-ENV PORT=4000
 ENV MIX_ENV="prod"
 
-CMD ["mix", "phx.server"]
+# Copy the final compiled release into the runtime stage
+COPY --from=builder --chown=1008:1008 /app/_build/${MIX_ENV}/rel/gc_index_relay ./
+
+USER 1008
+
+# Run the compiled binary
+CMD ["/app/bin/server"]