title: Error updating Dockerfile FROM php:7.2-fpm to php:7.3-fpm
body: <p>Because I want PHP 7.3 features I am trying to update the project from PHP 7.2 to PHP 7.3. Within docker-compose.yml I have:</p>
  
  <pre><code>php:
      build: ./docker/php
      volumes:
          - .:/var/www/html
      links:
          - mysql:mysql
      depends_on:
          - mysql
      networks:
        - pimcorenet
  </code></pre>
  
  <p>My Dockerfile is like:</p>
  
  <pre><code>FROM php:7.2-fpm
  
  # install git
  RUN apt-get update &amp;&amp; \
          apt-get install -y --no-install-recommends git
  
  #install some base extensions
  RUN apt-get install -y \
          zlib1g-dev \
          zip \
          libpng-dev \
          exiftool \
          libfreetype6-dev \
          libjpeg62-turbo-dev \
          libmcrypt-dev \
          libicu-dev \
          libpq-dev \
          libxpm-dev \
          libvpx-dev \
          mariadb-client \
          libxml2-dev
  
  RUN docker-php-ext-install -j$(nproc) \
          zip \
          exif \
          bcmath \
          intl \
          pcntl \
          mysqli \
          pdo \
          gd \
          pdo_mysql \
          pdo_pgsql \
          mbstring \
          soap \
          opcache \
          iconv
  
  # Install Imagick
  RUN apt-get update &amp;&amp; apt-get install -y \
      libmagickwand-dev --no-install-recommends \
      &amp;&amp; pecl install imagick \
      &amp;&amp; docker-php-ext-enable imagick
  
  # Install Composer
  RUN echo "Install Composer"
  RUN curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer
  RUN composer --version
  </code></pre>
  
  <p>I am getting the following error:</p>
  
  <blockquote>
    <p>E: Failed to fetch
    <a href="http://cdn-fastly.deb.debian.org/debian/pool/main/r/readline/readline-common_7.0-5_all.deb" rel="nofollow noreferrer">http://cdn-fastly.deb.debian.org/debian/pool/main/r/readline/readline-common_7.0-5_all.deb</a>
    Could not resolve 'cdn-fastly.deb.debian.org' E: Failed to fetch
    <a href="http://cdn-fastly.deb.debian.org/debian/pool/main/j/jquery/libjs-jquery_3.3.1~dfsg-3_all.deb" rel="nofollow noreferrer">http://cdn-fastly.deb.debian.org/debian/pool/main/j/jquery/libjs-jquery_3.3.1~dfsg-3_all.deb</a>
    Could not resolve 'cdn-fastly.deb.debian.org' E: Failed to fetch
    <a href="http://cdn-fastly.deb.debian.org/debian/pool/main/f/freetype/freetype2-doc_2.9.1-3_all.deb" rel="nofollow noreferrer">http://cdn-fastly.deb.debian.org/debian/pool/main/f/freetype/freetype2-doc_2.9.1-3_all.deb</a>
    Could not resolve 'cdn-fastly.deb.debian.org' E: Failed to fetch
    <a href="http://cdn-fastly.deb.debian.org/debian/pool/main/i/icu/icu-devtools_63.1-6_amd64.deb" rel="nofollow noreferrer">http://cdn-fastly.deb.debian.org/debian/pool/main/i/icu/icu-devtools_63.1-6_amd64.deb</a>
    Could not resolve 'cdn-fastly.deb.debian.org' E: Failed to fetch
    <a href="http://cdn-fastly.deb.debian.org/debian/pool/main/j/javascript-common/javascript-common_11_all.deb" rel="nofollow noreferrer">http://cdn-fastly.deb.debian.org/debian/pool/main/j/javascript-common/javascript-common_11_all.deb</a>
    Could not resolve 'cdn-fastly.deb.debian.org' ..... more errors</p>
    
    <p>ERROR: Service 'php' failed to build: The command '/bin/sh -c apt-get
    install -y         zlib1g-dev         zip         libpng-dev<br>
    exiftool         libfreetype6-dev         libjpeg62-turbo-dev<br>
    libmcrypt-dev         libicu-dev         libpq-dev         libxpm-dev 
    libvpx-dev         mariadb-client         libxml2-dev' returned a
    non-zero code: 100</p>
  </blockquote>
  
  <p>What is the exact problem with this? Is it because some required PHP extensions are not yet available for PHP 7.3 or have been replaced? How do I resolve this? Just changed <code>FROM php:7.2-fpm</code> to <code>FROM php:7.3-fpm</code>. </p>