How setup location block to strip port from url - nginx

Question

I'm trying to setup nginx to reverse proxy to a port dynamically based on port found in path.
So https://my-nginx.uksouth.cloudapp.azure.com/58585/some/route goes to https://localhost:58585/some/route
And https://my-nginx.uksouth.cloudapp.azure.com/59595/some/route goes to
https://localhost:59595/some/route
I can hard code the config like this
server {
server_tokens off;
server_name my-nginx.uksouth.cloudapp.azure.com;
listen [::]:443 ssl ipv6only=on; # managed by Certbot
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/my-nginx.uksouth.cloudapp.azure.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/my-nginx.uksouth.cloudapp.azure.com/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
location /58585 {
proxy_pass http://localhost:58585/;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto https;
proxy_redirect off;
}
location /59595 {
proxy_pass http://localhost:59595/;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto https;
proxy_redirect off;
}
}
server {
if ($host = my-nginx.uksouth.cloudapp.azure.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
listen 80 default_server;
listen [::]:80 default_server;
server_name my-nginx.uksouth.cloudapp.azure.com;
return 404; # managed by Certbot
}
and reverse proxy like this
ssh -R 58585:localhost:58585 myuser#my-nginx.uksouth.cloudapp.azure.com
ssh -R 59595:localhost:59595 myuser#my-nginx.uksouth.cloudapp.azure.com
This works as expected; then I've tried to make this dynamic
So https://my-nginx.uksouth.cloudapp.azure.com/targetPort/some/route goes to https://localhost:$targetPort/some/route
The best I can come up with is the following but this keeps failing and with a 502 bad gateway.
location ~ /([0-9]+) {
set $targetPort $1;
proxy_pass http://localhost:$targetPort/;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto https;
proxy_redirect off;
}
Can someone guide me with the correct way to do this ?
Thanks!

Answer 1

According to documentation:
In some cases, the part of a request URI to be replaced cannot be determined:
When location is specified using a regular expression, and also inside named locations.
In these cases, proxy_pass should be specified without a URI.
I think you can try to use rewrite here to specify an URI:
location ~ ^/(\d+) {
set $targetPort $1;
rewrite /\d+(.*) $1 break;
proxy_pass http://localhost:$targetPort;
...
}
Maybe this can be optimized for one regex matching instead of two:
location ~ ^/(\d+)(.*) {
set $targetPort $1;
set $newuri $2;
rewrite . $newuri break;
proxy_pass http://localhost:$targetPort;
...
}
But it needs to be tested, nginx behavior is unpredictable sometimes.
Update
This is definitely can be optimized to
location ~ ^/(?<targetPort>\d+)(?<newURI>.*) {
rewrite . $newURI break;
proxy_pass http://localhost:$targetPort;
...
}