Simplify kuksa-client docker build and reducing resulting image size

[SebastianSchildt]

This fixes #682

On a high level

• switch to a glibc build
• this reduced build times as grpc wheels exist
• as a side effect the existing glibc wheels are already small
• using pyinstaller only ship the parts of python necessary to run the client, thus reducing size over using a python base image

This fixes the huge size of the arm image, while at the same time even reducing the amd64 image compared to master

Arm64 size now

ttl.sh/kuksa.val/kuksa-client-ff43b39d56fff605c6330c078dea4b383cade50f        latest                 e2dce0b872fd   About a minute ago   73.1MB

[erikbosch]

Should we possibly document our strategy (and experiences) for Docker environments somewhere. Like, should we stop using alpine everywhere? Today we have a quite big mix, and are there not some possible benefits of using the same environment as often as possible?

[SebastianSchildt]

"probably", although I think it might differ depending on technology

So "historically" there was Alpine used, as for the C++ Val-Server it really made a difference size-wise.

For Python based things the savings are not that large, and using glibc builds are just easiest. Current stable debian just seems a common choice in many docker workloads. The solution here basically already includes learnings from the past , e.g. the pyinstaller technique from DBC feeder, except it does not condense all pyinstaller collected things in one file (as it does not offer benefits inside a container, but a runtime penalty unpacking it)

For rust it is a bit different, as we are using "from scratch" images (e.g. only one binary in the container, no distro), and glibc isn't really suited to be statically linked - you CAN do it, but then some rust crates/dependecies break that, hence we have MUSL there.

tldr; We should, I think this on represents our current "best practice" in pyhton, and maybe we should adapt our python stuff

[erikbosch]

I did a very basic check:

• Download container
• Start it and verify that KUKSA client starts and connect successfully to Databroker (insecure mode)
  That worked, that is good enough for me

[SebastianSchildt]

I tested secure. lgtm.