Docker + older version of Elixir/Phoenix
That looks like bitwalker/alpine-elixir issue 5:
when using tagged images, you may sometimes need to explicitly upgrade packages, as the installed packages are at the versions found when building the image.
Generally it's as simple as addingapk --update upgradebefore any commands which install packages.
Indeed, when you compare the old elixir 1.4.4-based Dockerfile, and the latest one, you will see an upgrade first in the latter:
apk --no-cache --update upgrade && \apk add --no-cache --update --virtual .elixir-build \...Try and add that to your Dockerfile.