title: Docker PHP Addons E: Package 'php-json' has no installation candidate
body: <p>Today I tried to install some PHP extensions for the default php docker container. My dockerfile looks like this:</p>
  
  <pre><code>FROM php:7.2-cli
  #remove apt install restriction
  RUN rm /etc/apt/preferences.d/no-debian-php
  
  #Install php-addons
  RUN apt-get update \
  &amp;&amp; apt-get install -y php-zip php-xml php-json php-mbstring
  
  COPY . /
  WORKDIR /
  </code></pre>
  
  <p>I got 2 errors by default.</p>
  
  <blockquote>
    <p>Err:1 <a href="http://deb.debian.org/debian" rel="nofollow noreferrer">http://deb.debian.org/debian</a> stretch InRelease
      Temporary failure resolving 'deb.debian.org'
    Could not resolve 'archive.ubuntu.com'</p>
  </blockquote>
  
  <p>AND</p>
  
  <blockquote>
    <p>E: Package 'php-json' has no installation candidate</p>
  </blockquote>