Using njs to fetch environment variables

nginx_njs_environment_variables.md

There are many ways to parse in variable into the nginx config file. Some uses set_by_lua which is offered by lua-nginx-module. Some use envstubst to populate varilabes into a template file.

Today I am going to show you how to do that with njs the JS scripting engine for nginx.

## /etc/nginx/fetch_env.js
function fetch_upstream_host(r) {
  return process.env.UPSTREAM_HOST;
}

function fetch_upstream_port(r) {
  return process.env.UPSTREAM_PORT;
}

## /etc/nginx/nginx.conf
load_module modules/ngx_http_js_module.so;

env UPSTREAM_HOST;
env UPSTREAM_PORT;

http {
  js_include fetch_env.js;
  js_set $upstream_host fetch_upstream_host;
  js_set $upstream_port fetch_upstream_port;

  server {
    # ....

    location / {
      # ....

      proxy_pass http://$upstream_host:$upstream_port;
    }
  }
}