Current Docker Exploration

docker-compose.yml

version: '2'
services:
  db:
    image: kiasaki/alpine-postgres
    volumes:
      - ./pgdata:/pgdata
    ports:
      - "5432:5432"
    environment:
      POSTGRES_DB: quarterly_development
      POSTGRES_USER: postgres
      PGDATA: /pgdata
  redis:
    image: redis
  web:
    build: .
    links:
      - db
      - redis
    volumes:
      - .:/home/quarterly/repo
      - ./keys:/root/.ssh/
    ports:
      - '9393:9393'
    env_file:
      - .env
    environment:
      REDIS_URL: redis://redis:6379
    restart: always
    command: foreman start

Dockerfile

FROM ruby:2.1.8-alpine
MAINTAINER DW & Braidn <itsallbroken@godynamo.com>
# Env
ENV REFRESHED_AT 2016-09-21
ENV PROJECT_NAME quarterly
ENV REPO_DIR /home/$PROJECT_NAME/repo
ENV GEM_HOME /home/$PROJECT_NAME/gems
ENV ENV_FILE /home/$PROJECT_NAME/repo/.env
ENV BUILD_PACKAGES bash libffi-dev openssl-dev linux-headers zlib-dev readline-dev yaml-dev git curl-dev ruby-dev build-base
ENV RUBY_PACKAGES ruby-io-console ruby-bundler nodejs libxml2-dev libxslt-dev postgresql-dev
# Build all required packages
RUN apk update && \
    apk upgrade && \
    apk add $BUILD_PACKAGES && \
    apk add $RUBY_PACKAGES && \
    rm -rf /var/cache/apk/*
# Create and switch to repo dir
RUN mkdir -p $GEM_HOME $REPO_DIR
WORKDIR $REPO_DIR
# Copy the rest of the app
ADD . $REPO_DIR
# Symlink vendor
RUN ln -sn /home/$PROJECT_NAME/repo/vendor/bundle $GEM_HOME
# Install gems. Bundler won't allow us to install with documentation.
#### NOTE: In production, the bundle command should be appended with `--without development test`
COPY Gemfile* $REPO_DIR/
# Nokogiri FTW
RUN bundle config build.nokogiri --use-system-libraries
# Set some defaults for bundler
ENV BUNDLE_GEMFILE=$REPO_DIR/Gemfile \
  BUNDLE_JOBS=6 \
  BUNDLE_PATH=$GEM_HOME
# Bundle ALL the gems
RUN gem install bundler && gem install tzinfo-data && bundle install
# Provide a Healthcheck for Docker risk mitigation
HEALTHCHECK --interval=3600s --timeout=20s --retries=2 CMD curl http://localhost:3000 || exit 1
# Define an entrypoint for default
ENTRYPOINT ["bundle", "exec"]
# Default command, running app as a service 
CMD ["bundle", "exec", "foreman", "start"]

What's the elevator pitch for using the Alpine distro vs Ubuntu?