Nginx realip module $lb_if_proxied variable: "-" if proxied, otherwise the load balancer's IP address

realip.nginx.conf

  # Create new variable $lb_if_proxied.
  #
  # With the realip module enabled, $remote_addr will be the end-user's IP
  # address, potentially from X-Forwarded-For, and $realip_remote_addr will be
  # the actual immediate client IP address.
  #
  # Return the load balancer IP address ($realip_remote_addr) if the request
  # looks like it was proxied. If the request does not look like it was proxied
  # (when $remote_addr is a private IP address), then return "-" instead.
  map $remote_addr $lb_if_proxied {
    "~^127\." "-";
    "~^10\." "-";
    "~^172\.1[6-9]\." "-";
    "~^172\.2[0-9]\." "-";
    "~^172\.3[0-1]\." "-";
    "~^192\.168\." "-";
    default $realip_remote_addr;
  }