title: Load a site based on header request in NGINX
body: <p>I have different static sites hosted at <code>http://static.example.com/</code> and
  I want to load different versions of the site based on the <code>X-Site-version</code> header sent to Nginx server. If no header is present than a default version should be loaded.</p>
  <p><strong>PSEUDO CODE</strong></p>
  <pre><code>if header X-Site-version === 2
   load /www/static/v2
  
  if header X-Siter-version === 1
   load /www/static/v1
  
  else
   load /www/static/v0
  </code></pre>