Image size: reduce number of layers

[gipert]

Our Docker image is huge.

We should try reducing the number of layers, if we want a smaller image: https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#minimize-the-number-of-layers. There are many layers (for example, installing apt packages) that can be merged into a single one.

Might also consider using this? https://github.com/dockerce/docker-slim

[oschulz]

That's a very good point. The fairly fine grained layers are there make it more maintainable, but slimmer afterwards could definitely be an option. But if we want to move to Podman, maybe there's other tooling available too, afterwards?