How to use environment variables in nginx config with Docker Compose?

nginx Docker image can extract environment variables before it starts, which can be leveraged to use environment variables in the nginx config, but it comes with a few caveats.

This repo demonstrates a way of setting it up with Docker Compose. The flow is:

1. Add env variables to you nginx.conf file.
2. Copy it to /etc/nginx/templates/nginx.conf.template in the container (as opposed to your normal /etc/nginx).
3. 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.

Example

Run

No Dockerfile version

docker compose up nginx-no-dockerfile

Dockerfile version

docker compose build nginx-with-dockerfile
docker compose up nginx-with-dockerfile

Test

Go to http://localhost:8081/example or http://localhost:8082/example depending on the version. You should see the contents of http://example.com proxied with the use of the environment variable.