Switch to Alpine

Dockerfile

@@ -1,29 +1,27 @@
-# LTS Image
-FROM ubuntu:18.04
+FROM ruby:alpine
 
 LABEL maintainer="github.google-sre-ebook@captnemo.in"
 
-ARG DEBIAN_FRONTEND="noninteractive"
+RUN apk add \
+    build-base \
+    linux-headers \
+    wget \
+    bash
+
+# Install pandoc
+RUN wget -nv https://github.com/jgm/pandoc/releases/download/2.5/pandoc-2.5-linux.tar.gz \
+    && tar xzf pandoc-2.5-linux.tar.gz --strip-components 1 -C /usr/local \
+    && rm pandoc-2.5-linux.tar.gz
+
+COPY Gemfile* /tmp/
+
+WORKDIR /tmp
+
+RUN gem install bundler --no-document \
+    && bundle install
 
 WORKDIR /src
 
-RUN apt-get update && apt-get install -y --no-install-recommends \
-    build-essential \
-    calibre \
-    pandoc \
-    ruby \
-    ruby-dev \
-    wget \
-    zlib1g-dev \
-    file \
-    && gem install bundler --no-ri --no-rdoc \
-    && apt-get clean \
-    && rm -rf /var/lib/apt/lists/*
-
-COPY . /src/
-
-RUN bundle install
-
 ENTRYPOINT ["/src/bootstrap.sh", "docker"]
 
 VOLUME ["/output"]