Add Dockerfile

Dockerfile

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+FROM hexpm/elixir:1.13.3-erlang-23.2.3-alpine-3.15.0 as build
+
+WORKDIR /app
+
+RUN apk add gcc git librdkafka-dev musl-dev
+
+# install Hex + Rebar
+RUN mix do local.hex --force, local.rebar --force
+
+# set build ENV
+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
+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
+RUN mix release
+
+# prepare release image
+FROM hexpm/elixir:1.13.3-erlang-23.2.3-alpine-3.15.0 AS app
+
+# install runtime dependencies
+#RUN apk add --update bash openssl postgresql-client
+
+EXPOSE 4000
+ENV MIX_ENV=prod
+
+# prepare app directory
+RUN mkdir /app
+WORKDIR /app
+
+# 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"]