You can use three new variables in custom request and response headers for Application Load Balancers:

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.