Regex plus variable in Nginx `proxy_redirect`

[brsolomon-deloitte@…]

It is not currently documented or apparent if it is possible to use a regex that also includes Nginx variables in proxy_redirect.

For example, none of these work:

proxy_redirect ~*https?://\\$proxy_host/(.*)$ /app1/$1
proxy_redirect ~*https?://\$proxy_host/(.*)$ /app1/$1
proxy_redirect ~*https?://$proxy_host/(.*)$ /app1/$1

This is described here in further detail: ​https://stackoverflow.com/q/70205048/7954504

The use-case for this is the scenario where one only wants to change Location header when the redirect location is for the internal app, not for an external redirect.

[brsolomon-deloitte@…]

It looks like the answer is no, based on ​https://github.com/openresty/replace-filter-nginx-module/issues/5. It seems worthwhile to document that.

[Maxim Dounin]

Agreed, it probably worth explicitly documenting that variables cannot be used within a regular expression, especially given that without regular expressions variables are allowed in the redirect string.

Note well that the original task can be better solved by a pair of proxy_redirect directives, without using regular expressions:

proxy_redirect http://$proxy_host/ /app1/;
proxy_redirect https://$proxy_host/ /app1/;

Further, proxy_redirect default; (which is the default) should work, though it will only handle the exact protocol used in proxying, not both http and https.