Jenkins – Interpolate Environment Variables Inside Dockerfile

From the official Nginx docker file:

Using environment variables in nginx configuration:

Out-of-the-box, Nginx doesn't support using environment variables inside most configuration blocks.

But envsubst may be used as a workaround if you need to generate your nginx configuration dynamically before nginx starts.

Here is an example using docker-compose.yml:

image: nginx
volumes:
 - ./mysite.template:/etc/nginx/conf.d/mysite.template
ports:
 - "8080:80"
environment:
 - NGINX_HOST=foobar.com
 - NGINX_PORT=80
command: /bin/bash -c "envsubst < /etc/nginx/conf.d/mysite.template > /etc/nginx/conf.d/default.conf && nginx -g 'daemon off;'" 

The mysite.template file may then contain variable references like this :

listen ${NGINX_PORT};

Update:

But you know this caused to its Nginx variables like this:

proxy_set_header        X-Forwarded-Host $host;

damaged to:

proxy_set_header        X-Forwarded-Host ;

So, to prevent that, i use this trick:

I have a script to run Nginx, that used on the docker-compose file as command option for Nginx server, i named it run_nginx.sh:

#!/usr/bin/env bash
export DOLLAR='$'
envsubst < nginx.conf.template > /etc/nginx/nginx.conf
nginx -g "daemon off;"

And because of defined new DOLLAR variable on run_nginx.sh script, now content of my nginx.conf.template file for Nginx itself variable is like this:

proxy_set_header        X-Forwarded-Host ${DOLLAR}host;

And for my defined variable is like this:

server_name  ${WEB_DOMAIN} www.${WEB_DOMAIN};

Also here, there is my real use case for that.

I am deleting my previous answer as I was answering something completely different. I found your problem, its the http://127.0.0.1 and ports which is wrong, 127.0.0.1 inside nginx's conf means the httpd container itself in this case not the host.

If you re-define that to server_jenkins and clients_jenkins and also suffix the 8080 port for both of those, then it should work.

server {
    listen       8080;
    server_name server.build.example.com;
    root /tmp;

    location / {
        proxy_pass   http://server_jenkins:8080;
    }
}
server {
    listen       8080;
    server_name clients.build.example.com;
    root /tmp;

    location / {
        proxy_pass   http://clients_jenkins:8080;
    }
}

Also, I noticed that the http directive causes errors, but as you mentioned the file you have provided can be just a snippet.