This page is served by the header-echo/1.0 origin server running on host 3bacd26aa932. It is designed to demonstrate how Envoy's ext\_proc filter can inspect and transform both headers and body content in real time. The origin application at internal.example.com returns raw upstream responses that the edge proxy reshapes before they reach the client.

 In production, body rewrite rules are used to replace legacy hostnames such as legacy.bigip.local with their public equivalents, redact internal identifiers like internal-build-9876, and patch version strings (e.g. appserver/3.2.1) without redeploying the backend. All replacements happen at the edge in a single streaming pass with no full-body buffering.