refactor docker image building

build/Dockerfile

@@ -0,0 +1,17 @@
+# borrowed from https://github.com/BretFisher/jekyll-serve
+
+FROM ruby:2.7-alpine
+
+RUN apk add --no-cache build-base gcc bash cmake git
+RUN apk add --no-cache imagemagick
+
+# install both bundler 1.x and 2.x
+RUN gem install bundler -v "~>1.0" && gem install bundler jekyll
+
+EXPOSE 4000
+
+WORKDIR /site
+
+ENTRYPOINT [ "jekyll" ]
+
+CMD [ "--help" ]

build/Dockerfile-serve

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+FROM docker.rzen.dev/jekyll:latest
+
+COPY docker-entrypoint.sh /usr/local/bin/
+
+# on every container start, check if Gemfile exists and warn if it's missing
+ENTRYPOINT [ "docker-entrypoint.sh" ]
+
+CMD [ "bundle", "exec", "jekyll", "serve", "--force_polling", "-H", "0.0.0.0", "-P", "4000" ]

build/docker-entrypoint.sh

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+#!/bin/bash
+set -e
+
+if [ ! -f Gemfile ]; then
+  echo "NOTE: hmm, I don't see a Gemfile so I don't think there's a jekyll site here"
+  echo "Either you didn't mount a volume, or you mounted it incorrectly."
+  echo "Be sure you're in your jekyll site root and use something like this to launch"
+  echo ""
+  echo "docker run -p 80:4000 -v \$(pwd):/site bretfisher/jekyll-serve"
+  echo ""
+  echo "NOTE: To create a new site, you can use the sister image bretfisher/jekyll like:"
+  echo ""
+  echo "docker run -v \$(pwd):/site bretfisher/jekyll new ."
+  exit 1
+fi
+
+bundle install --retry 5 --jobs 20
+
+exec "$@"