If I build an image using the Dockerfile in the blog post 10 days later, there is no guarantee that my application would work. The packages in Ubuntu's repositories might be updated to new versions that are buggy/no longer compatible with my application.

OP's suggestion is to build a separate image with required packages, tag it with something like "mybaseimage:25032022" and use it as my base image in the Dockerfile. This way, no matter when I rebuild the Dockerfile, my application will always work. You can rebuild the base image and application's image every X days to apply security patches and such. This also means I now have to maintain two images instead of one.

Another option is to use an image tag like "ubuntu:impish-20220316" (instead of "ubuntu:21.10") as base image and pin the versions of the packages you are installing via apt.

I personally don't do this since core packages in Ubuntu's repositories rarely introduce breaking changes in the same version. Of course, this depends on package maintainers, so YYMV.