Nginx location redirect to destination URL obtained from a different server

Question

In my current scenario there are a dozen domains with a PHP redirect script set up on them that obtains the destination URL from a SQL database based on the $_SERVER['QUERY_STRING'] parameter passed in the URL initially requested by the User.

NginX is configured like this on each of these servers (which we'll call Domains_A/B/C):

        location /r/ {
            rewrite ^/r/(.*)$ /r/index.php?$1;
        }

So the request goes like User > Domains_A/B/C > Destination URL

But what I would like is to not have to duplicate the PHP redirect script and keep this script on a single domain. This may be obtained by doing something like this:

Domains_A/B/C

        location /r/ {
            rewrite ^/r/(.*)$ https://Domain_X/r/index.php?$1;
        }

Domain_X (with PHP redirect script)

        location /r/ {
            rewrite ^/r/(.*)$ /r/index.php?$1;
        }

But this multiplies the redirects as User > Domain_A/B/C > Domain_X (with PHP redirect script) > Destination URL. And also the Referer sent to Destination URL is Domain_X which is something I am trying to avoid.

I would like to not multiply the redirects and to keep Domains_A/B/C as the Referer too. As in have NginX obtain the destination URL from Domain_X when Domains_A/B/C are accessed and point the redirect directly at the Destination URL from Domains_A/B/C.

Something along these lines on Domains_A/B/C:

        location /r/ {
            set Destination_URL get from https://Domain_X/r/index.php?$1;
            rewrite ^/r/(.*)$ Destination_URL;
        }

Is this possible? I was not able to find a solution yet.

Answer 1

You can proxy_pass the request to the domain that has the redirect script:

On Domains_A/B/C:

location /r/(.*)$ {
    proxy_pass https://Domain_X/r/index.php?$1;
}

Or (in my installations it worked only like this)

location ~ ^/r/(.*)$ {
    proxy_set_header Host PHP_SCRIPT_DOMAIN_NAME;
    proxy_pass https://PHP_SCRIPT_DOMAIN_IP:443/r/index.php?$1;
}

And on Domain_X (which has the PHP script).

location /r/ {
    rewrite ^/r/(.*)$ /r/index.php?$1;
}