Questions[nginx](server)

I have a docker container running Nginx, that links to another docker container. The host name and IP address of the second container is loaded into the Nginx container as environment variables on startup, but is not know before then (it's dynamic). I want my nginx.conf to use these values - e.g.

upstream gunicorn {
    server $APP_HOST_NAME:$APP_HOST_PORT;
}

How can I get environment variables into the Nginx configuration on startup?

EDIT 1

This is the entire file, after the suggested answer below:

env APP_WEB_1_PORT_5000_TCP_ADDR;
# Nginx host configuration for django_app

# Django app is served by Gunicorn, running under port 5000 (via Foreman)
upstream gunicorn {
    server $ENV{"APP_WEB_1_PORT_5000_TCP_ADDR"}:5000;
}

server {
    listen 80;

    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log;

    location /static/ {
        alias /app/static/;
    }
    location /media/ {
        alias /app/media/;
    }
    location / {
        proxy_pass http://gunicorn;
    }
}

Reloading nginx then errors:

$ nginx -s reload
nginx: [emerg] unknown directive "env" in /etc/nginx/sites-enabled/default:1

EDIT 2: more details

Current environment variables

root@87ede56e0b11:/# env | grep APP_WEB_1
APP_WEB_1_NAME=/furious_turing/app_web_1
APP_WEB_1_PORT=tcp://172.17.0.63:5000
APP_WEB_1_PORT_5000_TCP=tcp://172.17.0.63:5000
APP_WEB_1_PORT_5000_TCP_PROTO=tcp
APP_WEB_1_PORT_5000_TCP_PORT=5000
APP_WEB_1_PORT_5000_TCP_ADDR=172.17.0.63

Root nginx.conf:

root@87ede56e0b11:/# head /etc/nginx/nginx.conf
user www-data;
worker_processes 4;
pid /var/run/nginx.pid;
env APP_WEB_1_PORT_5000_TCP_ADDR;

Site nginx configuration:

root@87ede56e0b11:/# head /etc/nginx/sites-available/default
# Django app is served by Gunicorn, running under port 5000 (via Foreman)
upstream gunicorn {
    server $ENV{"APP_WEB_1_PORT_5000_TCP_ADDR"}:5000;
}

server {
    listen 80;

Reload nginx configuration:

root@87ede56e0b11:/# nginx -s reload
nginx: [emerg] directive "server" is not terminated by ";" in /etc/nginx/sites-enabled/default:3

Nginx is running on port 80, and I'm using it to reverse proxy URLs with path /foo to port 3200 this way:

location /foo {
                proxy_pass http://localhost:3200;
                proxy_redirect     off;
                proxy_set_header   Host $host;
}

This works fine, but I have an application on port 3200, for which I don't want the initial /foo to be sent to. That is - when I access http://localhost/foo/bar, I want only /bar to be the path as received by the app. So I tried adding this line to the location block above:

rewrite ^(.*)foo(.*)$ http://localhost:3200/$2 permanent;

This causes 302 redirect (change in URL), but I want 301. What should I do?

I'm looking for an overly simplified answer to the following question. I'm trying to build a foundational understanding of how Nginx works alongside something like Gunicorn.

Do I need both Nginx and something like Gunicorn to deploy Django apps on Nginx?

If so, what actually handles the HTTP requests?

Ps. I don't want to use Apache and mod_wsgi!

How can I check what modules have been added to an nginx installation?

I want to rewrite all http requests on my web server to be https requests, I started with the following:

server {
    listen      80;

    location / {
      rewrite     ^(.*)   https://mysite.com$1 permanent;
    }
...

One Problem is that this strips away any subdomain information (e.g., node1.mysite.com/folder), how could I rewrite the above to reroute everything to https and maintain the sub-domain?