Nginx: log the actual forwarded proxy_pass request URI to upstream

Question

I've got the following nginx conf:

http {

  log_format upstream_logging '[proxied request] '
                              '$server_name$request_uri -> $upstream_addr';
  
  access_log /dev/stdout upstream_logging;

  server {

    listen 80;
    server_name localhost;
    
    location ~ /test/(.*)/foo {
      proxy_pass http://127.0.0.1:3000/$1;
    }
  }
}

When I hit:

http://localhost/test/bar/foo

My actual output is:

[proxied request] localhost/test/bar/foo -> 127.0.0.1:3000 

While my expected output is:

[proxied request] localhost/test/bar/foo -> 127.0.0.1:3000/bar

Is there a variable or a way to produce the actual proxied URI in the log?

Answer 1

If not production, you can test what is being sent by nginx after launching the simplest listening server on the desired local address and port (instead of a real one):

$ nc -l 127.0.0.1 3000
POST /some/uri HTTP/1.0
Host: 127.0.0.1
Connection: close
Content-Length: 14

some payload

Response can be simulated by manually entering HTTP/1.1 200 OK, followed with 2 new lines, while nc is running.

Answer 2

I have used tcpflow -cg directly inside my NGINX docker. It has a lot of output, but the interesting part is this one:

172.023.000.001.37378-172.023.000.007.00080: GET /react/home.html HTTP/1.1
Host: localhost
[...]

172.023.000.007.49748-172.023.000.002.01234: GET /home.html HTTP/1.0
Host: website-react:1234
[...]

From this you can read: http://localhost/react/home.html --> http://website-react:1234/home.html