nginx: use environment variables

Question

I have the following scenario: I have an env variable $SOME_IP defined and want to use it in a nginx block. Referring to the nginx documentation I use the env directive in the nginx.conf file like the following:

user www-data; worker_processes 4; pid /run/nginx.pid;  env SOME_IP; 

Now I want to use the variable for a proxy_pass. I tried it like the following:

location / {     proxy_pass http://$SOME_IP:8000; } 

But I end up with this error message: nginx: [emerg] unknown "some_ip" variable

Answer 1

With NGINX Docker image

Apply envsubst on template of the configuration file at container start. envsubst is included in official NGINX docker images.

Environment variable is referenced in a form $VARIABLE or ${VARIABLE}.

nginx.conf.template:

user  nginx; worker_processes  1;  error_log  /var/log/nginx/error.log warn; pid        /var/run/nginx.pid;  events {     worker_connections  1024; }  http {     server {         listen       80;         location / {             access_log off;             return 200 '${MESSAGE}';             add_header Content-Type text/plain;         }     } } 

Dockerfile:

FROM nginx:1.17.8-alpine COPY ./nginx.conf.template /nginx.conf.template CMD ["/bin/sh" , "-c" , "envsubst < /nginx.conf.template > /etc/nginx/nginx.conf && exec nginx -g 'daemon off;'"] 

Build and run docker:

docker build -t foo . docker run --rm -it --name foo -p 8080:80 -e MESSAGE="Hellou World" foo 

NOTE:If config template contains dollar sign $ which should not be substituted then list all used variables as parameter of envsubst so that only those are replaced. E.g.:

CMD ["/bin/sh" , "-c" , "envsubst '$USER_NAME $PASSWORD $KEY' < /nginx.conf.template > /etc/nginx/nginx.conf && exec nginx -g 'daemon off;'"] 

Nginx Docker documentation for reference. Look for Using environment variables in nginx configuration.

Using environment variables in nginx configuration

Out-of-the-box, nginx doesn’t support 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:

web:   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 && exec nginx -g 'daemon off;'" 

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

listen ${NGINX_PORT};

Answer 2

You can access the variables via modules - I found options for doing it with Lua and Perl.

Wrote about it on my company's blog:

https://web.archive.org/web/20170712003702/https://docs.apitools.com/blog/2014/07/02/using-environment-variables-in-nginx-conf.html

The TL;DR:

env API_KEY; 

And then:

http { ...   server {     location / {       # set var using Lua       set_by_lua $api_key 'return os.getenv("API_KEY")';        # set var using perl       perl_set $api_key 'sub { return $ENV{"API_KEY"}; }';       ...     }   } } 

EDIT: original blog is dead, changed link to wayback machine cache