Nginx reverse proxy to server that's specified in the path - nginx

Question

I have an nginx reverse proxy location setup like so:
location /192.168.0.10 {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Host $server_name;
proxy_cookie_path /phpmyadmin/ /;
proxy_redirect off;
proxy_pass http://192.168.0.10/;
}
location /192.168.0.11 {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Host $server_name;
proxy_cookie_path /phpmyadmin/ /;
proxy_redirect off;
proxy_pass http://192.168.0.11/;
}
location /192.168.0.12 {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Host $server_name;
proxy_cookie_path /phpmyadmin/ /;
proxy_redirect off;
proxy_pass http://192.168.0.12/;
}
location /192.168.0.13 {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Host $server_name;
proxy_cookie_path /phpmyadmin/ /;
proxy_redirect off;
proxy_pass http://192.168.0.13/;
}
location /192.168.0.14 {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Host $server_name;
proxy_cookie_path /phpmyadmin/ /;
proxy_redirect off;
proxy_pass http://192.168.0.14/;
}
location /192.168.0.15 {.....
This structure repeats about 96 times so that we can have a reverse proxy to each one. Is there a way to simplify it so that there is only one structure and that the IP in the location's path magically just appears in the proxy_pass directive? Because this is becoming a pain to manage as we add and remove servers.

Answer 1

I think the following regex matching location should work:
location ~ ^/(?<proxy>192\.168\.0\.(?:10|11|12|13|14|15|...))(?:/(?<path>.*))?$ {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Host $server_name;
proxy_cookie_path /phpmyadmin/ /;
proxy_redirect off;
proxy_pass http://$proxy/$path;
}
You can additionally optimize that non-capturing group (?:10|11|12|13|14|15|...), for example to match any number from 10 to 105 it can be written as (?:10[0-5]|[1-9]\d).
Update 1
As requested by OP, PCRE regex for any IPv4 address with strict checking (for matching only correct IPv4 addresses from 0.0.0.0 to 255.255.255.255, adapted from this answer) can be written as
location ~ "^/(?<proxy>(?:25[0-5]|2[0-4]\d|[01]?\d?\d\.){3}(?:25[0-5]|2[0-4]\d|[01]?\d?\d))(?:/(?<path>.*))?$" {
...
}
Due to the curly brackets usage regex pattern must be enclosed in double quotes.
Update 2
Previous solutions won't preserve the request query string, more correct solution to keep all the request query arguments is to use proxy_pass http://$proxy/$path$is_args$args directive:
location ~ "^/(?<proxy>(?:25[0-5]|2[0-4]\d|[01]?\d?\d\.){3}(?:25[0-5]|2[0-4]\d|[01]?\d?\d))(?:/(?<path>.*))?$" {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Host $server_name;
proxy_cookie_path /phpmyadmin/ /;
proxy_redirect off;
proxy_pass http://$proxy/$path$is_args$args;
}