Dockerfile.musl

# platforms: linux/x86_64
FROM ruby:2.1.10-alpine

# A few RUN actions in Dockerfiles are subject to uncontrollable outside
# variability: an identical command would be the same from `docker build`'s
# point of view but does not indicate the result would be identical at
# different points in time.
#
# This causes two possible issues:
#
# - one wants to capture a new state and so wants the identical
#   non-reproducible command to produce a new result. This could be achieved
#   with --no-cache but this affects every single operation in a Dockerfile
# - one wants to identify a specific state and leverage caching at that
#   specific state.
#
# To that end a BUILD_ARG is introduced to capture an arbitrary identifier of
# that state (typically time) that is introduced in non-reproducible commands
# to make them appear different to Docker.
#
# Of course it only works when caching data is available: two independent
# builds with the same value and no cache shared would produce different
# results.
ARG REPRO_RUN_KEY=0

# `apk update` is uncontrolled and fetches whatever is today's index.
# For the sake of reproducibility subsequent steps (including in dependent
# images) should not do `apk update`, instead this base image should be
# updated by changing the `REPRO_RUN_KEY`.
RUN true "${REPRO_RUN_KEY}" && apk update

ENV LANG=en_US.UTF-8

## Install a pinned RubyGems and Bundler
RUN gem update --system 2.7.11
RUN gem install bundler --version 1.17.3

# Install additional gems that are in CRuby but missing from the above
# JRuby install distribution. These are version-pinned for reproducibility.
RUN gem install rake:12.3.3