title: How to inject environment variables in Varnish configuration
body: <p>I have 2 environments variables :</p>
  
  <pre><code>echo $FRONT1_PORT_8080_TCP_ADDR # 172.17.1.80
  echo $FRONT2_PORT_8081_TCP_ADDR # 172.17.1.77
  </code></pre>
  
  <p>I want to inject them in a my default.vcl like : </p>
  
  <pre><code>backend front1 {
      .host = $FRONT1_PORT_8080_TCP_ADDR;
  }
  </code></pre>
  
  <p>But I got an syntax error on the <code>$</code> char.</p>
  
  <p>I've also tried with <a href="https://www.varnish-cache.org/vmod/variable-support" rel="noreferrer">user variables</a> but I can't define them outside <code>vcl_recv</code>.</p>
  
  <p>How can I retrieve my 2 values in the VCL ?</p>