How can I render a specific node as the content for the maintenance page?

Question

Given a nid X, how do I have Drupal render it as the content for the maintenance page?

Answer 1

Use the Twig tweak module and create an overwrite template for maintenance-page.html.twig. Then copy & paste stuff from your base theme, but replace {{ page.content }} from the base theme with {{ drupal_entity('node', X) }}

E.g. for stable 9 theme this would look like

<header role="banner">
  {% if logo %}
    <a href="{{ front_page }}" title="{{ 'Home'|t }}" rel="home">
      <img src="{{ logo }}" alt="{{ 'Home'|t }}"/>
    </a>
  {% endif %}

  {% if site_name or site_slogan %}
    {% if site_name %}
      <h1>
        <a href="{{ front_page }}" title="{{ 'Home'|t }}" rel="home">{{ site_name }}</a>
      </h1>
    {% endif %}

    {% if site_slogan %}
      <div>{{ site_slogan }}</div>
    {% endif %}
  {% endif %}
</header>

<main role="main">
  {% if title %}
    <h1>{{ title }}</h1>
  {% endif %}

  {{ page.highlighted }}

  {# disabled {page.content} here #}
  {{ drupal_entity('node', X) }}
</main>

{% if page.sidebar_first %}
  <aside role="complementary">
    {{ page.sidebar_first }}
  </aside>
{% endif %}

{% if page.sidebar_second %}
  <aside role="complementary">
    {{ page.sidebar_second }}
  </aside>
{% endif %}

{% if page.footer %}
  <footer role="contentinfo">
    {{ page.footer }}
  </footer>
{% endif %}

Answer 2

In order to customize the Maintenace Page in Drupal 8/9 We need to do following items but not restricted to:

1. Create a Basic Page or Article in Drupal for Maintenance page and keep its node id in handy

2. Update settings.php to include your custom theme machine name in the config value like: $settings['maintenance_theme'] = 'your_theme_machine_name';

3. Copy maintenance-page.html.twig from batrik theme or core/modules/system/templates/maintenance-page.html.twig and keep at your_theme_name/templates/system/maintenance-page.html.twig

4. Update your maintenance-page.html.twig as in below snippet to embed the content you have in place from Article/Basic page in 1st step

    {#
    /**
     * @file
     * Bartik's theme implementation to display a single Drupal page while offline.
     *
     * All available variables are mirrored in page.html.twig.
     *
     * @see template_preprocess_maintenance_page()
     */
     #}
   
     <header role="banner">
       {% if logo %}
         <a href="{{ front_page }}" title="{{ 'Home'|t }}" rel="home">
           <img src="{{ logo }}" alt="{{ 'Home'|t }}"/>
         </a>
       {% endif %}
    </header>
   
   
    <article{{ attributes }}>
      {% block article_title %}
        <div class="container">
           <div class="row">
             <div class="col-12 col-xs-12">
               <div class="s-inner-content">                
                 {# disabled {page.content} here #}
                 {# render body field from Article or Basic page with specific node id #}
                 {{ drupal_field('body', 'node', nid) }}                
               </div>
             </div>
           </div>  
        </div>
      {% endblock %}
   
   </article>
   

In order to have some static page like maintenance-page--ofline.html.twig in drupal 8/9 as in Drupal 7 when Database is down we need to refer to the ongoing discussion on issues: https://www.drupal.org/project/drupal/issues/2720109

We can also refer existing discussion: Drupal 8 maintenance page theming