Alpine Linux Dockerfile, adds Ruby 2.2 using ruby-install

alpine_ruby-2.2.dockerfile

# Alpine with Ruby 2.2

FROM alpine:3.7

RUN apk upgrade --no-cache --update && \
    apk add --no-cache --update ca-certificates make bash build-base
RUN cd /tmp && \
    wget -O - https://github.com/postmodern/ruby-install/archive/v0.6.1.tar.gz | tar xzvf - && \
    ( cd ruby-install-0.6.1 && \
      make install ) && \
    rm -rf ruby-install-*
RUN ruby-install --cleanup ruby 2.2

RUN addgroup app && \
    adduser -D -G app -h /app -s /bin/sh app

USER app
WORKDIR /app