ProxyPassReverse

ProxyPassReverse is a directive in the Apache HTTP Server, part of the mod_proxy module, used in reverse proxy configurations to rewrite certain response headers so that the client sees URLs tied to the proxy rather than the backend server. It does not alter the request sent to the backend, only the response returned to the client.

In operation, when a proxied backend returns a redirect or a resource URL that points to its own host, ProxyPassReverse rewrites those header values to reflect the proxy’s public URL space. This helps preserve a consistent URL experience for clients and prevents exposure of internal hostnames.

Syntax and usage are short and straightforward. The typical form is per mapping: ProxyPassReverse [path] URL. For example:

ProxyPass /app http://backend.example.com/app

ProxyPassReverse /app http://backend.example.com/app

or

ProxyPass / http://backend.example.local/

ProxyPassReverse / http://backend.example.local/

Headers affected are primarily Location and Content-Location, which carry absolute URLs, but the directive may be extended with related cookie directives if needed. Related directives include ProxyPassReverseCookiePath and ProxyPassReverseCookieDomain, which adjust cookie paths and domains in responses from the backend.

Use of ProxyPassReverse is recommended whenever a reverse proxy forwards requests to a backend server that generates absolute URLs in its responses. It ensures that clients interact with URLs that map to the proxy rather than to the backend, maintaining proper navigation and redirection across the proxy boundary.