Docker Container, Custom Index. Html on Startup

Been dealing with this problem for 2 days already, don't understand why it won't create the file. Cannot find any info on this online.

Task

Design an apache container that creates a custom index.html file with container's hostname in it (for load balancing testing) on startup.

Basically I need it to run 'uname -n > /var/www/html/index.html' on startup. But no matter what I do file is not created.

Tried

Running this script in Dockerfile's CMD/ENTRYPOINT:

#!/bin/bash
apachectl -DFOREGROUND
/bin/uname -n | tee /var/www/html/index.html

and

#!/bin/bash
apachectl -DFOREGROUND
/bin/uname -n > /var/www/html/index.html

Apache starts but file is not there.

But if I start container with just ENTRYPOINT and then attach to it and run the same script that was copied during build - it creates the file...

Tried keeping only ENTRYPOINT ["apachectl","-DFOREGROUND"] and running needed command with 'docker run ...', but then apache doesn't start and container exits right away.

I'm confused. Please, any help will be greatly appreciated.