How to configure nginx to act as a load balancer for proxies?

Question

I am aware that nginx can be configured to act as a load balancer, but I'm wondering if it is possible to load balance between proxies? Let's say I have multiple proxies running on localhost, and I want to use nginx to provide a single point of connection so that I can rotate between the proxies. I am trying to achieve something similar to the post here, which is using HAProxy instead of nginx. I have the following nginx.conf:

events {  }

http {
    upstream proxies {
        server localhost:9998;
        server localhost:9999;
        server localhost:10000;
    }
    server {
        listen 8080;

        location / {
            proxy_pass http://proxies;
        }
    }
}

However, when I send a curl request like this:

curl http://icanhazip.com -x localhost:8080

It ignores the url, and I get a response similar to what I would expect if I had directly sent a request to one of the proxy servers like so:

curl localhost:9999

Of course, I did not really expect it to work, since there must be some option to tell nginx to treat the upstream servers as proxies themselves. However, I was not able to find how to do this after searching online.

Answer 1

The nginx docs say upstreams are distributed using a round-robin method.

By default, requests are distributed between the servers using a weighted round-robin balancing method

https://nginx.org/en/docs/http/ngx_http_upstream_module.html

Answer 2

as you can see in your haproxy post haproxy akt as a forward proxy

option http_proxy

What this option mean is described in the manual https://cbonte.github.io/haproxy-dconv/1.6/configuration.html#4-option%20http_proxy

It sometimes happens that people need a pure HTTP proxy which understands basic proxy requests without caching nor any fancy feature. In this case, it may be worth setting up an HAProxy instance with the "option http_proxy" set. In this mode, no server is declared, and the connection is forwarded to the IP address and port found in the URL after the "http://" scheme.

No host address resolution is performed, so this only works when pure IP addresses are passed. Since this option's usage perimeter is rather limited, it will probably be used only by experts who know they need exactly it. This is incompatible with the HTTP tunnel mode.

As far as I know nginx does not have this feature.

A similar question it this. https://superuser.com/questions/604352/nginx-as-forward-proxy-for-https

Why can't you use the haproxy as described in the post of your link?