Nginx regex location not matching

Question

I am serving some services on an Ubuntu VM using Nginx 1.14.0. In my server definition, I'm including a location block designed to forward requests from /api/v{version}/users{suffix} where version is supposed to be a number like 1.0 or 2.1 and suffix can be empty or could be part of the route. My goal is to forward to localhost:5006/v{version}/users{suffix}. The reason I'm doing things this way is that I also have /api/v{version}/rooms{suffix} and /api/v{version}/prompts{suffix} and these go to separate ports. Currently, my location block looks like this:

location ~ ^\/api\/v(([0-9]+)\.([0-9]+))\/users(.*)$ {
    proxy_pass https://localhost:5006/v$1/users$2;
    proxy_http_version 1.1;
    proxy_pass_request_headers on;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';
    proxy_set_header Host $host;
    proxy_cache_bypass $http_upgrade;
}

However, when I try to call /api/v1.0/users/31245 I get a 502 and, on inspection of my error logs, I see this:

[error] 2591#2591: *6052 no resolver defined to resolve localhost, client: [MY_IP_ADDR], server: [SERVER_NAME], request: "GET /api/v1.0/users/158015ab-3811-4137-8a13-102d9b400050 HTTP/1.1"

This appears to be happening because the request couldn't be matched to a location. I've tested this on several different Nginx testers and it seems to work so what am I doing wrong here?

Answer 1

Using variables within the proxy_pass statement requires Nginx to use a resolver. See this document for details.

Either specify a resolver statement, or better still, rewrite the block to avoid using variables in the proxy_pass statement.

For example:

location ~ ^/api/v[0-9]+\.[0-9]+/users {
    rewrite ^/api(.*)$ $1 break;
    proxy_pass https://localhost:5006;
    ...
}