Docker configuration for TelemetryMetricsStatsd

defmodule StatsdDemoWeb.Telemetry do
  use Supervisor
  import Telemetry.Metrics

  def start_link(arg) do
    Supervisor.start_link(__MODULE__, arg, name: __MODULE__)
  end

  @impl true
  def init(_arg) do
    children = [
      {TelemetryMetricsStatsd, metrics: metrics(), formatter: :datadog, port: 8125}
    ]

    Supervisor.init(children, strategy: :one_for_one)
  end

  def metrics do
    [
      # Phoenix Metrics
      summary("phoenix.endpoint.stop.duration",
        unit: {:native, :millisecond}
      ),
      summary("phoenix.router_dispatch.stop.duration",
        tags: [:route],
        unit: {:native, :millisecond}
      ),
      counter("phoenix.socket_connected.count",
        tags: [:endpoint]
      ),

      # VM Metrics
      summary("vm.memory.total", unit: {:byte, :kilobyte}),
      summary("vm.total_run_queue_lengths.total"),
      summary("vm.total_run_queue_lengths.cpu"),
      summary("vm.total_run_queue_lengths.io")
    ]
  end
end

# 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:1.14.0-erlang-25.1-debian-bullseye-20210902-slim
#
ARG ELIXIR_VERSION=1.14.0
ARG OTP_VERSION=25.1
ARG DEBIAN_VERSION=bullseye-20220801-slim

ARG NODE_BULDER_IMAGE="node:18.3.0-alpine3.16"
ARG ELIXIR_BUILDER_IMAGE="hexpm/elixir:${ELIXIR_VERSION}-erlang-${OTP_VERSION}-debian-${DEBIAN_VERSION}"
ARG RUNNER_IMAGE="debian:${DEBIAN_VERSION}"

########################################
# 1. Node build stage
########################################
FROM ${NODE_BULDER_IMAGE} as node-builder

# prepare build dir
WORKDIR /app
RUN mkdir assets

# set build ENV
ENV NODE_ENV=prod

# install npm dependencies
COPY ./services/statsd_demo/assets/package.json ./assets/
COPY ./services/statsd_demo/assets/package-lock.json ./assets/
RUN npm install --prefix assets

########################################
# 2. Elixir build stage
########################################
FROM ${ELIXIR_BUILDER_IMAGE} as elixir-builder

# install build dependencies
RUN apt-get update -y && apt-get install -y build-essential git \
  && 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 ./services/statsd_demo/mix.exs ./
COPY ./services/statsd_demo/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 ./services/statsd_demo/config/config.exs config/
COPY ./services/statsd_demo/config/${MIX_ENV}.exs config/
RUN mix deps.compile

COPY ./services/statsd_demo/priv priv

COPY ./services/statsd_demo/lib lib

COPY ./services/statsd_demo/assets assets
COPY --from=node-builder /app/assets/node_modules assets/node_modules

# compile assets
RUN mix assets.deploy

# Compile the release
RUN mix compile

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

COPY ./services/statsd_demo/rel rel
RUN mix release

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

RUN apt-get update -y && apt-get install -y libstdc++6 openssl libncurses5 locales \
  && 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"

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

USER nobody

CMD ["/app/bin/server"]