How to pass environment variable to nginx.conf file in docker? - docker

Question

I am trying to setup ruby on rails with docker everything is good but i want dynamic domain pass as environment variable to nginx.conf file during build image by docker-compose command but i don't know how to do it.
i trying to use this command
Docker-compose build
dcoker-compose up
Docker File
FROM ruby:2.7.2
ENV RAILS_ROOT /var/www/quickcard
ENV BUNDLE_VERSION 2.1.4
ENV BUNDLE_PATH usr/local/bundle/gems
ENV RAILS_LOG_TO_STDOUT true
ENV RAILS_PORT 5000
COPY ./entrypoint.sh /usr/local/bin/entrypoint.sh
RUN chmod +x /usr/local/bin/entrypoint.sh
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
RUN apt-get update -qq && apt-get install -y build-essential \
git \
libxml2-dev \
libpq-dev \
libxslt-dev \
nodejs \
yarn \
imagemagick \
tzdata \
less \
cron \
&& rm -rf /var/cache/apk/*
RUN gem install bundler --version "$BUNDLE_VERSION"
RUN mkdir -p $RAILS_ROOT
WORKDIR $RAILS_ROOT
ADD Gemfile Gemfile
ADD Gemfile.lock Gemfile.lock
COPY yarn.lock yarn.lock
RUN bundle install
EXPOSE $RAILS_PORT
RUN ln -s $RAILS_ROOT/config/systemd/puma.service /etc/systemd/system/quickcard
COPY . .
RUN crontab -l | { cat; echo ""; } | crontab -
RUN yarn install
RUN yarn install --check-files
RUN ls /var/www/quickcard/public
ENTRYPOINT ["entrypoint.sh"]
CMD ["bundle", "exec", "puma", "-C", "config/puma.rb"]
Nginx Docker File
FROM nginx
RUN apt-get update -qq && apt-get -y install apache2-utils
ENV RAILS_ROOT /var/www/quickcard
WORKDIR $RAILS_ROOT
RUN mkdir log
COPY public public/
COPY ./nginx.conf /etc/nginx/conf.d/default.conf
COPY ./multi_quickcard.key /etc/nginx/multi_quickcard.key
COPY ./quickcard-ssl-test.pem /etc/nginx/quickcard-ssl-test.pem
EXPOSE 80 443
CMD [ "nginx", "-g", "daemon off;" ]
Nginx.conf e.g
upstream puma {
# Path to Puma SOCK file, as defined previously
server app:5000 fail_timeout=0;
}
server {
listen 80;
server_name default_server;
index index.html index.htm;
try_files $uri $uri/ /index.html =404;
location / {
root /var/www/quickcard/public/;
proxy_pass http://puma;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
}
location /api {
root /var/www/quickcard/public/;
proxy_pass http://puma;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
}
location ^~ /assets/ {
root /var/www/quickcard/public/;
gzip_static on;
expires max;
add_header Cache-Control public;
}
error_page 500 502 503 504 /500.html;
client_max_body_size 4G;
keepalive_timeout 10;
}
Docker Compose File
version: '2.2'
services:
app:
build:
context: .
dockerfile: ./Dockerfile
command: bash -c "bundle exec rails s -p 5000 -e production -b 0.0.0.0 && RAILS_ENV=production bundle exec rake assets:precompile"
environment:
RAILS_ENV: production
volumes:
- /var/wwww/quickcard
- /var/wwww/quickcard/public
ports:
- 5000:5000
sidekiq:
build: .
command: bundle exec sidekiq -C config/sidekiq.yml
environment:
RAILS_ENV: production
volumes:
- /var/wwww/quickcard/tmp
cron_job:
build: .
command: cron -f
nginx:
build:
context: .
dockerfile: ./nginx.Dockerfile
volumes:
- ./log-nginx:/var/log/nginx/
restart: always
ports:
- 80:80
- 443:443

Answer 1

nginx Docker image can extract environment variables before it starts, but it's a bit tricky. One solution is to:
Add env variables to your nginx.conf file.
Copy it to /etc/nginx/templates/nginx.conf.template in the container (as opposed to your normal /etc/nginx) in the build step or as a volume.
Set the NGINX_ENVSUBST_OUTPUT_DIR: /etc/nginx environment variable in docker-compose.yml.
This will cause the nginx.conf.template file to be copied to /etc/nginx as nginx.conf and the environment variables will be replaced with their values.
There is one caveat to keep in mind: using command property in docker-compose.yml seems to be disabling the extraction functionality. If you need to run a custom command to start-up nginx, you can use the Dockerfile version.
I created a repo with the full setup, but in case it's not available:
# docker-compose.yml
version: "3"
services:
nginx-no-dockerfile:
container_name: nginx-no-dockerfile
image: nginx:1.23.1-alpine
ports:
- 8081:80
volumes:
- ./site/index.html:/usr/share/nginx/html/index.html
- ./site/nginx.conf:/etc/nginx/templates/nginx.conf.template
working_dir: /usr/share/nginx/html
environment:
NGINX_ENVSUBST_OUTPUT_DIR: /etc/nginx
API_URL: http://example.com
nginx-with-dockerfile:
container_name: nginx-with-dockerfile
build:
context: ./site
dockerfile: ./Dockerfile
ports:
- 8082:80
volumes:
- ./site/index.html:/usr/share/nginx/html/index.html
environment:
NGINX_ENVSUBST_OUTPUT_DIR: /etc/nginx
API_URL: http://example.com
# site/nginx.conf
worker_processes auto;
events {
}
http {
include /etc/nginx/mime.types;
server {
listen 80;
root /usr/share/nginx/html;
index index.html index.htm;
location / {
try_files $uri $uri/ /index.html;
}
location /example {
proxy_pass $API_URL;
}
}
}
# site/Dockerfile
FROM nginx:1.23.1-alpine
WORKDIR /usr/share/nginx/html
COPY ./nginx.conf /etc/nginx/templates/nginx.conf.template
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]
Run no Dockerfile version: docker compose up nginx-no-dockerfile
Run Dockerfile version:
docker compose build nginx-with-dockerfile
docker compose up nginx-with-dockerfile
Make sure to also have index.html file in the site folder.

Answer 2

The recommended approach Nginx seems to be to use the envsubst utility. You would need to create a template file with the variable placed inside as $Variable or {Variable}. You could then pass into envsubst the template file which would render the variable from the environment.
This has a few downsides in that it can potentially replace nginx variables unintentionally so I would make sure to pass in the specific variables you would want to replace.
See this question which addresses a similar problem for more details: https://serverfault.com/questions/577370/how-can-i-use-environment-variables-in-nginx-conf