Dynamic default.conf of nginx in docker

Question

This is my default.conf I'm replacing the original default.conf with the following one in my Dockerfile.

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

server {

    listen 443;
    server_name $servername;

    ssl_certificate           /etc/ssl/private/server.crt;
    ssl_certificate_key       /etc/ssl/private/server.key;

    ssl on;

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

    location / {

      proxy_set_header        Host $host;
      proxy_set_header        X-Real-IP $remote_addr;
      proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header        X-Forwarded-Proto $scheme;

      proxy_pass          http://xxx:2368;
      proxy_read_timeout  90;

      proxy_redirect      http://xxx:2368 https://$servername:443;
    }
}

The error I receive is

2017/06/26 21:08:15 [emerg] 1#1: unknown "servername" variable
nginx: [emerg] unknown "servername" variable

When I replace $servername with 192.168.xx.xx (the real IP of my server), than everything works fine. But I want it to be dynamic.

How can I define the value of the $servername so that my docker will pick it up and it will be used by nginx?

Or can I write my default.conf in another way to make this dynamic?

minamijoyo · Accepted Answer · 2017-06-28 15:36:55Z

10

Use envsubst to dynamically embed environment variables in the nginx configuration. envsubst is a lightweight template engine and it is also included in the official nginx:alpine image.

To install envsubst to your custom image:

alpine:

$ apk --no-cache add gettext

debian:

$ apt-get install gettext-base

Here is a simple example for how to use envsubst:

$ cat test.conf.template
hoge=$HOGE

$ docker run --rm \
    -v $(pwd)/test.conf.template:/tmp/test.conf.template \
    -e HOGE=aaa \
    nginx:alpine \
    /bin/sh -c "envsubst < /tmp/test.conf.template > /tmp/test.conf && cat /tmp/test.conf"
hoge=aaa

Note that if you want to use the $ symbol in the configuration file like nginx.conf, you need to specify the name of the environment variable to embed.

An example of dynamically embedding the environment variable SERVER_NAME in nginx.conf is as follows:

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

server {

    listen 443;
    server_name ${SERVER_NAME};

    ssl_certificate           /etc/ssl/private/server.crt;
    ssl_certificate_key       /etc/ssl/private/server.key;

    ssl on;

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

    location / {

      proxy_set_header        Host $host;
      proxy_set_header        X-Real-IP $remote_addr;
      proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header        X-Forwarded-Proto $scheme;

      proxy_pass          http://xxx:2368;
      proxy_read_timeout  90;

      proxy_redirect      http://xxx:2368 https://${SERVER_NAME}:443;
    }
}

The arguments are somewhat complicated, so it is shown here in docker-compose.yml format:

version: '2'
services:
  nginx:
    image: nginx:alpine
    command: >
      /bin/sh -c
      "envsubst '
      $$SERVER_NAME
      '< /etc/nginx/nginx.conf.template
      > /etc/nginx/nginx.conf
      && nginx -g 'daemon off;'"
    volumes:
      - ./nginx.conf.template:/etc/nginx/nginx.conf.template
    ports:
      - 8080:80
    environment:
      SERVER_NAME: "test.example.com"

answered Jun 28, 2017 at 15:36

minamijoyo

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2 Comments

Frondor Over a year ago

Hi, thank you for this! I'm wondering how can I do this same thing but using multiple template files? For example, I have a ssl.conf file that I want to include in several server blocks so I clean the code a bit. How can I use env vars in that file as well? I think an extra envsubst call is needed, right? And what about moving everything to an entrypoint.sh file to clean the command a little bit? Thanks in advance

Falldog Hsieh Over a year ago

I think you can try below solution dcinja, it's better to handle the complex case, stackoverflow.com/a/65412923/6857874

Falldog Hsieh · Accepted Answer · 2022-08-24 14:54:44Z

Maybe you can try dcinja, it's my open-source project

dcinja use inja powerful library (like jinja) as template engine for run-time render template. It's support condition & include feature, that envsubst can't provided. Need to install dcinja in your docker image, and the binary is small.

here is the simple example

alpine:

$ apk --no-cache add wget libstdc++
$ wget https://github.com/Falldog/dcinja/releases/download/v1.3/dcinja-1.3.alpine.tar.gz \
    && tar xvzf dcinja-1.3.alpine.tar.gz
$ ./dcinja -j '{"SERVER_NAME": "www.test.com"}' -s /etc/nginx/nginx.conf.template -d /etc/nginx/nginx.conf

debian:

$ apt-get update && apt-get install -y wget
$ wget https://github.com/Falldog/dcinja/releases/download/v1.3/dcinja-1.3.linux-amd64.tar.gz \
    && tar xvzf dcinja-1.3.linux-amd64.tar.gz
$ ./dcinja -j '{"SERVER_NAME": "www.test.com"}' -s /etc/nginx/nginx.conf.template -d /etc/nginx/nginx.conf

Example

An example of dynamically embedding the environment variable SERVER_NAME in nginx.conf is as follows:

nginx.conf.template

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

server {

    listen 443;
    server_name {{ SERVER_NAME }};

    ssl_certificate           /etc/ssl/private/server.crt;
    ssl_certificate_key       /etc/ssl/private/server.key;

    ssl on;

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

    location / {

      proxy_set_header        Host $host;
      proxy_set_header        X-Real-IP $remote_addr;
      proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header        X-Forwarded-Proto $scheme;

      proxy_pass          http://xxx:2368;
      proxy_read_timeout  90;

      proxy_redirect      http://xxx:2368 https://{{ SERVER_NAME }}:443;
    }
}

Dockerfile

need to build the image with dcinja library

FROM nginx:1.21-alpine
RUN apk add --no-cache wget libstdc++
RUN mkdir -p /app \
    && cd /app \
    && wget https://github.com/Falldog/dcinja/releases/download/v1.3/dcinja-1.3.alpine.tar.gz \
    && tar xvzf dcinja-1.3.alpine.tar.gz \
    && cp /app/dcinja /bin/

docker-compose.yml

You can assign the the env SERVER_NAME at docker-compose to control the runtime result of nginx.conf

version: '2'
services:
  nginx:
    build: .
    image: my-nginx:latest
    container_name: my-nginx
    command: >
        /bin/sh -c "
            dcinja --force-system-envs -e SERVER_NAME \
                -s /etc/nginx/nginx.conf.template \
                -d /etc/nginx/nginx.conf \
            && nginx -g 'daemon off;'
        "
    volumes:
      - ./nginx.conf.template:/etc/nginx/nginx.conf.template
    ports:
      - 8080:80
    environment:
      SERVER_NAME: "test.example.com"

Complex template example

You can maintain 3 template files, 1) nginx.conf.template 2) https.conf.template 3) http.conf.template. Determine the flag (enable_ssl) to include the right template at runtime.

{% if enable_ssl %}
    {% include "https.conf.template" %}
{% else %}
    {% include "http.conf.template" %}
{% endif %}

Other dcinja examples

input template from STDIN, output template to STDOUT

$ echo "TEST Name: {{ name }}" | dcinja -j '{"name": "Foo"}'
>>> TEST Name: Foo

input template from file, output template to file

$ dcinja -j '{"name": "Foo"}' -s input.template -d output.template

input json from file

$ dcinja -f param.json -s input.template -d output.template

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Dynamic default.conf of nginx in docker

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