Update to ubuntu 22.04, gdal 3.4, python 3.10

[corviday]

This branch updates ubuntu to 22.04, gdal to 3.4.1, and python to 3.10. It drops support for python 2.x, which gets tricker in ubuntu 22.04, and I don't think we're using it any more.

The goal was to fix the climate explorer backend build. Here is a demo of SCIP running with the fixed climate explorer backend built from this docker.

Aside from climate-explorer-backend, sandpiper seems to be the only repository currently using this container. It appears to be using a custom branch named "gdal3" and probably won't be affected by this update, though since this update has gdal 3.4, perhaps we should see if it can use this one as well so we have one fewer build to maintain.

[rod-glover]

Aside from climate-explorer-backend, sandpiper seems to be the only repository currently using this container. It appears to be using a custom branch named "gdal3" and probably won't be affected by this update, though since this update has gdal 3.4, perhaps we should see if it can use this one as well so we have one fewer build to maintain.

Excellent idea.

[rod-glover]

This looks good.

A couple of small items for thought, especially given the remarks on build time, etc., this morning:

• One is generally speaking encouraged to reduce the number of layers created in a Dockerfile. Each RUN command, amongst others, creates a new layer. Fewer layers can help reduce the final image size. That's why the original Dockerfile had the one RUN command with so many continuation lines.
• But more important is to order the RUN commands to exploit layer caching. The most reliable and the most expensive RUNs should come early in the Dockerfile, because when you rebuild an image, Docker uses the layer cache to only build what's necessary. If you are fiddling with some item and it can go towards the end of a Dockerfile, it should, because your (re)builds will be much quicker than if it comes early and invalidates caches from there on down. I don't know if this applies here, because naturally there are also constraints imposed by dependency relationships.

[Nospamas]

Echoing Rod's notes. Rolling the apt get and the caching purge into one line makes that layer overall smaller and seems to be the general best practice. In particular, purging caches before finishing the line lets docker finish layer with those caches already purged.

I was also going to suggest looking for a minimal ubuntu images but it looks like ubuntu images less than 30 megs and don't include a slim version. This is in contrast to something like debian which does publish separate slim images.

EDIT: this is also suggested in the best practices docker docs