WHat does Path.expand("./uploads/") return? Is it as expected and really the folder you have configured as target for copying the uploaded files to? relative pathes can be mean at times, especially if one isn’t careful or conscious about the actual working directory.

Sadly you haven’t told us how you are starting your application… That could give some hints about the actual working directory.

See this excerpt from the docs

The preferred form is to use :from with an atom or tuple, since it will make your application independent from the starting directory. For example, if you pass:

    plug Plug.Static, from: "priv/app/path"

Plug.Static will be unable to serve assets if you build releases or if you change the current directory. Instead do:

    plug Plug.Static, from: {:app_name, "priv/app/path"}

have you tried it with tuple?

@wojtekmach I should have mentioned I tried that as well without any luck.

@NobbZ The path I want to access is /app/uploads. Docker mounts the app in /app so if I run a remote console to the running app in production and do Path.expand("./uploads") I get the correct path: /app/uploads. Plus, Arc is able to write to the correct path without any further modifications.

I think posting my Docker file might help:

# Build Stage
FROM elixir:1.9 as build

ENV DEBIAN_FRONTEND=noninteractive
ENV HOME=/opt/app/ TERM=xterm

RUN \
  curl -sL https://deb.nodesource.com/setup_10.x | bash - && \
  curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - && \
  echo "deb http://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list && \
  apt-get update && apt-get -y install nodejs yarn

## Install Hex+Rebar
RUN mix local.hex --force && \
  mix local.rebar --force

WORKDIR /opt/app

ENV MIX_ENV=prod

## Cache elixir deps
RUN mkdir config
COPY config/* config/
COPY mix.exs mix.lock ./
RUN mix do deps.get, deps.compile

## Cache node deps
COPY assets/*.json ./assets/
COPY assets/yarn.lock ./assets/
RUN cd ./assets && yarn install

## Compile assests & create digest
COPY . .
RUN npm run deploy --prefix ./assets
RUN mix phx.digest

## Compile Elixir release
RUN MIX_ENV=prod mix distillery.release --env=prod

# Release Stage
FROM elixir:1.9-slim

EXPOSE 4000
ENV MIX_ENV=prod REPLACE_OS_VARS=true SHELL=/bin/sh

WORKDIR /app
COPY --from=build /opt/app/_build/prod/rel/c37 ./

ENTRYPOINT ["bin/c37"]

The app is started when docker-compose creates the web service with the foreground option

Really should set it to /app/uploads then, don’t use relative paths without the tuple format and even then only within an application itself, not outside of it. The CWD can change in unexpected ways in a massively concurrent system.

I am curious if Plug.Static requires things it is serving to be local though, hmm…

Thanks for the suggestion, but I already tried “hardcoding” the full path, and it did not work either.

Is it possible to define environment specific plugs, or would having 2 plugs be good enough? The paths are different on prod and dev, so if I hardcode them to “/app/uploads” dev breaks.

As plug is a macro, I’m not even sure if it resolve the path during compile time or runtime. Wrap an IO.insoect and watch application build as well as start carefully for output. The :label option is of great help for such things.

At compile-time for Plug.Static.

And I just tested it here with an absolute directory and it worked, so there is something else going on that’s possibly not related to the path for Plug.Static?

Yeah, I thought about that myself, but I really do not want to start a marathon of a debugging session when simply a Base64 encode of the image will solve my issues. Once this application gets more usage, uploaded assets will be stored on S3 anyways, but I just can’t fight this nagging feeling. What I’m trying to do should work.I just can’t figure out why.

Any chance at making an SSCCE that we can just git clone and spool up or so?

Are you working with a Docker image as well?