Phoenix Liveview - Assets out of container

Question

I'm struggling to do a Docker image in Phoenix 1.6 with Liveview and deploying with releases.

Running with mix phx.server everything goes fine but with a Dockerfile the assets are not loaded. Images and css/js files do not load.

The assets folder is copied with all the files and the mix assets.deploy compile the assets in the priv folder.

The Dockerfile. I'm using ESBuild to compile the assets.

ARG MIX_ENV="prod"

FROM hexpm/elixir:1.11.3-erlang-23.3.4.7-alpine-3.14.0 as build

# install build dependencies
RUN apk add --no-cache build-base git python3 curl

# prepare build dir
WORKDIR /app

# install hex + rebar
RUN mix local.hex --force && \
    mix local.rebar --force

# set build ENV
ARG MIX_ENV
ENV MIX_ENV="${MIX_ENV}"

# install mix dependencies
COPY mix.exs 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 config/config.exs config/$MIX_ENV.exs config/
RUN mix deps.compile

COPY priv priv

# note: if your project uses a tool like https://purgecss.com/,
# which customizes asset compilation based on what it finds in
# your Elixir templates, you will need to move the asset compilation
# step down so that `lib` is available.
COPY assets assets
RUN mix assets.deploy

# compile and build the release
COPY lib lib
RUN mix compile

# changes to config/runtime.exs don't require recompiling the code
COPY config/runtime.exs config/

COPY rel rel
RUN PORT=4001 mix release

# prepare release image
FROM alpine:3.12.1 AS app
RUN apk add --no-cache libstdc++ openssl ncurses-libs

ARG MIX_ENV
ENV USER="elixir"

WORKDIR "/home/${USER}/app"
# Creates an unprivileged user to be used exclusively to run the Phoenix app
RUN \
  addgroup \
   -g 1000 \
   -S "${USER}" \
  && adduser \
   -s /bin/sh \
   -u 1000 \
   -G "${USER}" \
   -h "/home/${USER}" \
   -D "${USER}" \
  && su "${USER}"

# Everything from this line onwards will run in the context of the unprivileged user.
USER "${USER}"

COPY --from=build --chown="${USER}":"${USER}" /app/_build/"${MIX_ENV}"/rel/acompanhante ./

ENTRYPOINT ["bin/acompanhante"]

# Usage:
#  * build: sudo docker image build -t elixir/my_app .
#  * shell: sudo docker container run --rm -it --entrypoint "" -p 127.0.0.1:4000:4000 elixir/my_app sh
#  * run:   sudo docker container run --rm -it -p 127.0.0.1:4000:4000 --name my_app elixir/my_app
#  * exec:  sudo docker container exec -it my_app sh
#  * logs:  sudo docker container logs --follow --tail 100 my_app
CMD ["start"]