Environment variables are not substituted in drupal.conf

Hello,

I am having trouble understanding how variable substitution works in the drupal.conf file.

When I build my Docker image from the Dockerfile, the drupal.conf file is correctly present inside the container, but it still contains the variables, for example:

DocumentRoot /var/www/html/${DOCROOT_FOLDER}

The values are not being substituted with the environment variables.

Inside the container, if I run:

echo ${DOCROOT_FOLDER}

I correctly get:

web

However, when I make a request to the Apache server, it attempts to serve index.php from:

/var/www/html

instead of:

/var/www/html/web

It seems as if Apache is not taking the environment variable into account.

Do you have any idea what I might be missing?

Thank you.