Make plan for deprecation of 20.04

[inglesp]

[bloodearnest]

These are the places I can find 20.04 usage:

r:v1 image

The old 4.0 version of R we are using is not built for 22.04. So we would have to find an alternative way to build R 4.0 to move to 22.04.

Think we should probably leave it as known issue, and document it in the repo.

python:v1 image

We could perhaps switch to using 22.04 - I've tested this works. This would change a handful of base libraries, but is likely backwards compatible - we could test this, with some effort perhaps.

base-docker

This produces the base-docker:20.04 and base-action:20.04 images. The public version these are EOL, and will not get any updates.

We maybe need to decide what to do here. We can't easily just remove the images as Github wont' let us as they're above the download threshold.

We could enable Ubuntu Pro, and get support for another 5 years, if we want to.

As long as we support r:v1 and python:v1 on 20.04, we will still need to publish this image. We don't need regular updates to pick up security fixes, but we may want to publish new versions of the few things we add on top, perhaps.

[bloodearnest]

I am currently spiking to figure out what it would take to use Ubuntu Pro to ignore this problem.

[bloodearnest]

We now have Ubuntu Pro licenses for our developer linux devices.

Canonical provided a pdf with more information, including this section:

9.2. Container images may be generated from Ubuntu Pro bits only if the resulting container images are deployed to Ubuntu Pro-covered machines.

So, this would mean that we would need Ubuntu Pro for TPP, EMIS, etc, at a minimum, to run the 20.04 images.

I have asked for clarification about Windows and Mac hosts, which AFAIK cannot have an Ubuntu Pro subscription. Have had no reply.

[bloodearnest]

Here is the detailed service description: https://assets.ubuntu.com/v1/f56994fc-ubuntu_pro_description_unified.pdf