Just a quick heads up: There seems to be a bug in Erlang/OTP 21.3, which can cause some errors when making http requests. If you’re using the official Elixir images that use Erlang/OTP 21 it might affect your app, because they got rebuilt with the latest version that contains the bug.

The quickest workaround is to instead of using FROM elixir:1.7.4 in your Dockerfile, replicate the elixir image layer and point it to an earlier image, for example 21.2.7:

FROM erlang:21.2.7

# elixir expects utf8.
ENV ELIXIR_VERSION="v1.7.4" \
	LANG=C.UTF-8

RUN set -xe \
	&& ELIXIR_DOWNLOAD_URL="https://github.com/elixir-lang/elixir/archive/${ELIXIR_VERSION}.tar.gz" \
	&& ELIXIR_DOWNLOAD_SHA256="c7c87983e03a1dcf20078141a22355e88dadb26b53d3f3f98b9a9268687f9e20" \
	&& curl -fSL -o elixir-src.tar.gz $ELIXIR_DOWNLOAD_URL \
	&& echo "$ELIXIR_DOWNLOAD_SHA256  elixir-src.tar.gz" | sha256sum -c - \
	&& mkdir -p /usr/local/src/elixir \
	&& tar -xzC /usr/local/src/elixir --strip-components=1 -f elixir-src.tar.gz \
	&& rm elixir-src.tar.gz \
	&& cd /usr/local/src/elixir \
	&& make install clean

CMD ["iex"]

Posting it here, because I know it affected more than just myself, might save some of you some time.