Substitute environment variables in NGINX config from docker-compose

Question

I am trying to start an NGINX server within a docker container configured through docker-compose. The catch is, however, that I would like to substitute an environment variable inside of the http section, specifically within the "upstream" block.

It would be awesome to have this working, because I have several other containers that are all configured through environment variables, and I have about 5 environments that need to be running at any given time. I have tried using "envsubst" (as suggested by the official NGINX docs), perl_set, and set_by_lua, however none of them appear to be working.

Below is the NGINX config, as it is after my most recent trial

user  nginx;
worker_processes  1;
env NGINXPROXY;

load_module modules/ngx_http_perl_module.so;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;


events {
    worker_connections  1024;
}

http {
    perl_set $nginxproxy 'sub { return $ENV{"NGINXPROXY"}; }';

    upstream api-upstream {
        server ${nginxproxy};
    }

    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;

    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile        off;
    #tcp_nopush     on;

    keepalive_timeout  65;

    #gzip  on;

    include /etc/nginx/conf.d/*.conf;
}

Below is the NGINX dockerfile

# build stage
FROM node:latest
WORKDIR /app
COPY ./ /app
RUN npm install
RUN npm run build

# production stage
FROM nginx:1.17.0-perl
COPY --from=0 /app/dist /usr/share/nginx/html
RUN apt-get update && apt-get install -y gettext-base
RUN rm /etc/nginx/conf.d/default.conf
RUN rm /etc/nginx/nginx.conf
COPY default.conf /etc/nginx/conf.d
COPY nginx.conf /etc/nginx
RUN mkdir /certs
EXPOSE 80 443
CMD ["nginx", "-g", "daemon off;"]

Below is the section of the docker-compose.yml for the NGINX server (with names and IPs changed). The envsubst command is intentionally commented out at this point in my troubleshooting.

front-end:
        environment:
            - NGINXPROXY=172.31.67.100:9300
        build: http://gitaccount:[email protected]/group/front-end.git#develop
        container_name: qa_front_end
        image: qa-front-end
        restart: always
        networks:
            qa_network:
                ipv4_address: 172.28.0.215
        ports:
            - "9080:80"
        # command: /bin/bash -c "envsubst '$$NGINXPROXY' < /etc/nginx/nginx.conf > /etc/nginx/nginx.conf && nginx -g 'daemon off;'"

What appears to be happening is when I reference the $nginxproxy variable in the upstream block (right after "server"), I get output that makes it look like it's referencing the string literal "$nginxproxy" rather than substituting the value of the variable.

qa3_front_end       | 2019/06/18 12:35:36 [emerg] 1#1: host not found in upstream "${nginx_upstream}" in /etc/nginx/nginx.conf:19
qa3_front_end       | nginx: [emerg] host not found in upstream "${nginx_upstream}" in /etc/nginx/nginx.conf:19
qa3_front_end exited with code 1

When I attempt to use envsubst, I get an error that makes it sound like the command messed with the format of the nginx.conf file

qa3_front_end       | 2019/06/18 12:49:02 [emerg] 1#1: no "events" section in configuration
qa3_front_end       | nginx: [emerg] no "events" section in configuration
qa3_front_end exited with code 1

I'm pretty stuck, so thanks in advance for your help.

Answer 1

Since nginx 1.19 you can now use environment variables in your configuration with docker-compose. I used the following setup:

# file: docker/nginx/templates/default.conf.conf
upstream api-upstream {
    server ${API_HOST};
}


# file: docker-compose.yml
services:
    nginx:
        image: nginx:1.19-alpine
        volumes:
            - "./docker/nginx/templates:/etc/nginx/templates/"
        environment:
            NGINX_ENVSUBST_TEMPLATE_SUFFIX: ".conf"
            API_HOST: api.example.com
        

I'm going off script a little from the example in the documentation. Note the extra .conf extension on the template file - this is not a typo. In the docs for the nginx image it is suggested to name the file, for example, default.conf.template. Upon startup, a script will take that file, substitute the environment variables, and then output the file to /etc/nginx/conf.d/ with the original file name, dropping the .template suffix.

By default that suffix is .template, but this breaks syntax highlighting unless you configure your editor. Instead, I specified .conf as the template suffix. If you only name your file default.conf the result will be a file named /etc/nginx/conf.d/default and your site won't be served as expected.