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Dockerfile

@@ -1,55 +1,76 @@
-FROM hexpm/elixir:1.13.3-erlang-23.2.3-alpine-3.15.0 as build
+# 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-20210902-slim - for the release image
+#   - https://pkgs.org/ - resource for finding needed packages
+#   - Ex: hexpm/elixir:1.13.3-erlang-23.2.3-debian-bullseye-20210902-slim
+#
+ARG DOCKER_IMAGE="hexpm/elixir:1.13.3-erlang-23.2.3-alpine-3.15.0"
 
-WORKDIR /app
 
+
+FROM ${DOCKER_IMAGE} as builder
+
+# install build dependencies
 RUN apk add gcc git librdkafka-dev musl-dev
 
-# install Hex + Rebar
-RUN mix do local.hex --force, local.rebar --force
+# prepare build dir
+WORKDIR /app
+
+# install hex + rebar
+RUN mix local.hex --force && \
+    mix local.rebar --force
 
 # set build ENV
-ENV MIX_ENV=prod
+ENV MIX_ENV="prod"
 
 # install mix dependencies
 COPY mix.exs mix.lock ./
-COPY config config
-RUN mix deps.get --only $MIX_ENV
-RUN DEBUG=1 mix deps.compile
-#
-## build assets
-#COPY assets assets
-#RUN cd assets && npm install && npm run deploy
-#RUN mix phx.digest
 
-# build project
-#COPY priv priv
+RUN mix deps.get --only $MIX_ENV
+RUN mkdir config
+
+# copy compile-time config files before we compile dependencies
+# to ensure any relevant config change will trigger the dependencies
+# to be re-compiled.
+COPY config/config.exs config/${MIX_ENV}.exs config/
+RUN mix deps.compile
+
+# Compile the release
 COPY lib lib
+
 RUN mix compile
 
-# build release
-# at this point we should copy the rel directory but
-# we are not using it so we can omit it
-# COPY rel rel
+# Changes to config/runtime.exs don't require recompiling the code
+COPY config/runtime.exs config/
+
+COPY rel rel
 RUN mix release
 
-# prepare release image
-FROM hexpm/elixir:1.13.3-erlang-23.2.3-alpine-3.15.0 AS app
+# start a new build stage so that the final image will only contain
+# the compiled release and other runtime necessities
+FROM ${DOCKER_IMAGE}
 
-# install runtime dependencies
-#RUN apk add --update bash openssl postgresql-client
+# Set the locale
+#RUN sed -i '/en_US.UTF-8/s/^# //g' /etc/locale.gen && locale-gen
 
-EXPOSE 4000
-ENV MIX_ENV=prod
+#ENV LANG en_US.UTF-8
+#ENV LANGUAGE en_US:en
+#ENV LC_ALL en_US.UTF-8
 
-# prepare app directory
-RUN mkdir /app
-WORKDIR /app
+WORKDIR "/app"
+RUN chown nobody /app
+
+# Only copy the final release from the build stage
+COPY --from=builder --chown=nobody:root /app/_build/prod/rel/kafkaex_lag_exporter ./
 
-# copy release to app container
-COPY --from=build /app/_build/prod/rel/kafkaex_lag_exporter .
-# COPY entrypoint.sh .
-RUN chown -R nobody: /app
 USER nobody
 
-ENV HOME=/app
-CMD ["/app/bin/kafkaex_lag_exporter", "start"]
+CMD ["/app/bin/server"]