Home » How can I use environment variables in Nginx.conf

How can I use environment variables in Nginx.conf

Solutons:


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.

The official nginx image recommends using envsubst, but as pointed out by others it will replace also $host and other variables, which is not desirable. But fortunately envsubst can take as a parameter the names of variables to replace.

To avoid a very complex command parameter to the container (as in the linked example), you can write a Docker entrypoint script which will fill in the environment variables before executing the command. The entrypoint script is also a good place for validating the parameters and setting default values.

Here is an example of an nginx container which takes in API_HOST and API_PORT parameters as environment variables.

nginx-default.conf.template

resolver  127.0.0.11 valid=10s;  # recover from the backend's IP changing

server {
  listen  80;

  location / {
    root  /usr/share/nginx/html;
  }

  location /api {
    proxy_pass  http://${API_HOST}:${API_PORT};
    proxy_set_header  Host $http_host;
  }
}

docker-entrypoint.sh

#!/usr/bin/env sh
set -eu

envsubst '${API_HOST} ${API_PORT}' < /etc/nginx/conf.d/default.conf.template > /etc/nginx/conf.d/default.conf

exec "$@"

Dockerfile

FROM nginx:1.15-alpine

COPY nginx-default.conf.template /etc/nginx/conf.d/default.conf.template

COPY docker-entrypoint.sh /
ENTRYPOINT ["/docker-entrypoint.sh"]
CMD ["nginx", "-g", "daemon off;"]

Doing this with Lua is substantially easier than it sounds:

server {
    set_by_lua $server_name 'return os.getenv("NGINX_SERVERNAME")';
}

I found that here:

https://docs.apitools.com/blog/2014/07/02/using-environment-variables-in-nginx-conf.html

Edit:

Apparently this requires installing the lua module: https://github.com/openresty/lua-nginx-module

Edit 2:

Note that with this approach you have to define env variable in Nginx:

env ENVIRONMENT_VARIABLE_NAME

You have to do this in toplevel context in nginx.conf or it won’t work! Not in server block or in config of some site in /etc/nginx/sites-available, because it is included by nginx.conf in http context (which is not top-level context).

Also note that with this approach if you try to make a redirect e.g.:

server {
    listen 80;
    server_name $server_name;
    return 301 https://$server_name$request_uri;
}

it won’t work as well:

2016/08/30 14:49:35 [emerg] 1#0: the duplicate "server_name" variable in /etc/nginx/sites-enabled/default:8

And if you give a separate variable name to it:

set_by_lua $server_name_from_env 'return os.getenv("NGINX_SERVERNAME")';

server {
    listen 80;
    server_name $server_name_from_env;
    return 301 https://$server_name$request_uri;
}

nginx won’t interpret it and will redirect you to https://%24server_name_from_env/.

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