"/usr/bin/php-cgi" appears to be missing

[bytebone]

I'm trying to get php working and am stuck at this problem. Let me write down some info on the setup:

• in lighttpd.conf i've enabled the modules alias, access and accesslog, and additionally am trying to include "mod_cgi.conf" and "mod_fastcgi.conf".
• I'm running the latest docker release under sebp/lighttpd in a docker environment, and the webserver is behind an nginx reverse proxy
• when uncommenting the "include fastcgi" line, the webserver will no longer start, since it's complaining about the php-cgi file missing: (gw_backend.c.1619) invalid "bin-path" => "/usr/bin/php-cgi" (check that file exists, is regular file, and is executable by lighttpd)
• while the container is running (without including fastcgi in the config), docker exec lighttpd ls /usr/bin | grep php returns nothing. I've also checked the ungrepped list of things, and there is no php-cgi link/file.
• my adjusted lighttpd.conf file is being linked into the container as a file link, instead of the whole config folder as is described in the docker compose section of the README. So the issue is not related to the "mod_fastcgi.conf" file provided by the image being overwritten by the config volume.

i've considered downloading the php-cgi file from an AUR or whatever the official source is and linking it into /usr/bin directly, but that seems so sloppy and prone to issues that I didn't dare to try. Is this behaviour intended? Am I missing something obvious? I've searched the web far and wide and was not able to find anything helpful on this, since nothing is related to the docker image. I hope you can swiftly assist me here.

Thanks in advance.

[spujadas]

Only lighttpd and lighttpd-mod_auth are installed in the image.
If you want to use PHP CGI, then first you’ll have to extend the image to install the corresponding package (look at the Dockerfile to see how this was done for lighttpd, and search for the package at https://pkgs.alpinelinux.org/packages).
Then your *.conf files should work properly.

[bytebone]

I see. So a rebuilding of the image is necessary? Can this somehow be done on a live install? I'm not too familiar with the inner workings of docker images and how to construct a Dockerfile, especially since I want to set up and run the image with docker compose, not a Dockerfile.

[spujadas]

You’ll indeed need to build an image based on the current one. You could then publish this image somewhere (e.g. your host, Docker Hub) to make it available for your live install.
Or based on the Dockerfile you’ve created to extend the image, you could also use docker compose to build and start the image directly from the Dockerfile.