environment variables in config files

[iridial]

Is this a new feature request?

• I have searched the existing issues

Wanted change

hello, would it be possible to use values set in environment variables inside nginx config? the official nginx container allows this by using templates: https://github.com/nginxinc/docker-nginx/blob/master/entrypoint/20-envsubst-on-templates.sh

for reference, this solution uses such feature:
https://serverfault.com/questions/577370/how-can-i-use-environment-variables-in-nginx-conf

docker-compose.yml:

version: "3.9"
services:
  nginx:
    image: nginx:1.23
    volumes:
        - ./template-variables:/etc/nginx/templates/10-variables.conf.template:ro

    environment:
        EXTERNAL_IP: "1.2.3.4"

template-variables:

map $host $external_ip {
  default "$EXTERNAL_IP";
}

nginx.conf:

server {
     location / {

          proxy_set_header X-Real-IP $external_ip;
      }
}

Reason for change

for instance, in a reverse proxy setup, if I need to set a secret which needs be passed in a request to the backend,
I'd like to set its value in the container env variables, instead of writing it in the nginx config directly.

proxy_set_header X-Api-Key $mysecret;

Proposed code change

No response

[github-actions]

Thanks for opening your first issue here! Be sure to follow the relevant issue templates, or risk having this issue marked as invalid.