Little trick to get AWS instance_id as variable in Nginx. Source: distinctplace.com/2014/07/22/little-trick-to-get-aws-instance_id-as-variable-in-nginx/

gistfile1.nginxconf

  perl_set  $instance_id  '
  sub  {
    if ($id)
    {
      # since this gets executed for EACH request, so use simple caching
      return $id;
    }

    # GET AWS instance metadata
    $id = `curl -s http://169.254.169.254/latest/meta-data/instance-id`;
    $id =~ s/(i\-)|(\s)//g;
    return $id;
  }
  ';