Consider using tagged base image

[Ponjimon]

The Dockerfile is using ubuntu as the base image but not using any tag. By default, this will use the latest tag which can change at any time to a newer version of ubuntu which can cause the image to break if there are breaking changes.

Consider using a tagged base image like ubuntu:focal (Ubuntu 20.04)

[oliverrahner]

... aaaaand it broke :D Ubuntu 22.04 doesn't ship default repository keys anymore. The easiest workaround is to fix ubuntu:focal as suggested.