Dockerfile: upgrade to Ubuntu 20.04 LTS

Dockerfile

-FROM ubuntu:bionic
+FROM ubuntu:focal AS nodejs_base
 
-LABEL maintainer="JP Stauffert"
+LABEL maintainer="andreas.knote@uni-wuerzburg.de"
 
-RUN apt-get update && apt-get install -y curl && \
+# set noninteractive installation
+ENV DEBIAN_FRONTEND noninteractive
+
+RUN apt-get update && apt-get upgrade && \
+    apt-get install -y \
+    curl ssh git-lfs build-essential locales
+
+RUN apt-get update && \
     curl -sL https://deb.nodesource.com/setup_13.x | bash - && \
-    apt-get update && apt-get install -y \
-    nodejs \
-    imagemagick \
-    ruby-full build-essential zlib1g-dev \
-    git-lfs ssh locales && \
+    apt-get install -y nodejs && \
+    echo 'Node: ' && \
+    node -v && \
+    echo 'NPM: ' && \
+    npm -v
+
+FROM nodejs_base AS ruby_jekyll
+
+RUN apt-get update && \
+    apt-get install -y \
+    ruby-full zlib1g-dev && \
     echo '# Install Ruby Gems to ~/gems' >> ~/.bashrc && \
     echo 'export GEM_HOME="$HOME/gems"' >> ~/.bashrc && \
     echo 'export PATH="$HOME/gems/bin:$PATH"' >> ~/.bashrc && \
-    gem update --system && \
     gem install jekyll bundler jekyll-redirect-from && \
-    echo 'Node: ' && \
-    node -v && \
-    echo 'NPM: ' && \
-    npm -v && \
     echo 'jekyll: ' && \
     jekyll -v && \
     echo 'gem: ' && \
-    gem -v && \
-    echo 'nodejs: ' && \
-    nodejs -v && \
-    locale-gen en_US.UTF-8 && \
+    gem -v 
+
+RUN locale-gen en_US.UTF-8 && \
     dpkg-reconfigure --frontend=noninteractive locales && \
     update-locale LANG="en_US.UTF-8" LANGUAGE="en_US" LC_CTYPE="en_US.UTF-8" LC_NUMERIC="en_US.UTF-8" LC_TIME="en_US.UTF-8" LC_COLLATE="en_US.UTF-8" LC_MONETARY="en_US.UTF-8" LC_MESSAGES="en_US.UTF-8" LC_PAPER="en_US.UTF-8" LC_NAME="en_US.UTF-8" LC_ADDRESS="en_US.UTF-8" LC_TELEPHONE="en_US.UTF-8" LC_MEASUREMENT="en_US.UTF-8" LC_IDENTIFICATION="en_US.UTF-8" LC_ALL="en_US.UTF-8" && \
     dpkg-reconfigure --frontend=noninteractive locales
+
 ENV LANG en_US.UTF-8 
 ENV LC_ALL en_US.UTF-8
 
+FROM ruby_jekyll AS image_resize
+
+RUN apt-get update && apt-get install -y \
+    imagemagick
+
+FROM image_resize AS hci_theme 
+
 ## Start prebuilding
 COPY package.json /
 RUN npm install --only=dev
@@ -39,4 +54,4 @@ RUN gem install bundler
 RUN bundle install
 RUN rake
 RUN rm -rf node_modules
-RUN rm package-lock.json
\ No newline at end of file
+RUN rm package-lock.json