Ubuntu Hirsute no longer supported: could I update the Dockerfile?

[3willows]

First, thank you Jeroen for a really wonderful book. The examples and pace are just right for me!

Second, the official Docker Image (from docker pull datasciencetoolbox/dsatcl2e) seems to use Ubuntu 21.0 (hirsute). (Cf. the result when I run lsb_release -a).

But this means that I cannot run sudo apt update because

E: The repository 'http://security.ubuntu.com/ubuntu hirsute-security Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.

I tried to get around it by changing the source to an archive for outdated ubuntu versions, cf. with this tip.

But with this solution, every time I restart the docker image, everything seems to just revert back. (I am new to Docker, so I am probably missing a trick or two with saving my changes properly).

But in any case, my understanding is that this is not an ideal solution because the archived ubuntu versions are no longer supported.

So, third, I am now looking for a way to update the Dockerfile, so that it installs the latest Ubuntu version instead.

I have had a look at the Docker Hub webpage, but all I can find is the image, not the file. I also tried looking both within the Docker image and also the github repository.

Am I correct that the Docker File is not publicly released? If not, would you consider doing so and potentially opening it for pull requests?

Thank you so much.

PS Apologies if any of the above betrayed confusion about Docker concepts: I will pick up your recommended further reading,"Docker Up and Running", next time I'm in the library!