You can use three new variables in custom request and response headers for

## Feature Feature You can use three new variables in custom request and response headers for Application Load Balancers: * `asn`: The Autonomous System Number (ASN) associated with the client's IP address. * `cloud_trace_id`: The trace ID extracted (or generated) from the HTTP request header. * `hostname`: The original hostname specified by the client in the `Host` HTTP request header. This allows preservation of the original host header (equivalent to `X-Forwarded-Host`). These variables are available for both global external Application Load Balancers and classic Application Load Balancers. For more information, see [Create custom headers in backend services](https://cloud.google.com/load-balancing/docs/https/custom-headers-global).