Optimise docker build

[lilatomic]

This MR restructures the dockerfiles so that it rebuilds fewer things when changing the scripts, resulting in performance improvements:

	current	optimised
fresh build	138.60	140.64
change pip requirements	70.39	16.82
change script	71.21	2.20

I started with this one because it's simpler than the geonode one.

[frafra]

Note that COPY has a --chmod option to make the file executable, while if you copy the file and then change its attributes, the file is going to be stored twice.

Edit: this is valid only when BUILDKIT is enabled, which is not yet the default.

[lilatomic]

oh neat, I didn't know about the (upcoming) --chmod, that's cool.
We could also change the permission of the files outside the container. thoughts?

I can combine the COPY instructions to reduce the number of layers. It reduces the number of layers, which I think helps with size (although I'm not clear on how big an impact this has).

[frafra]

We could also change the permission of the files outside the container. thoughts?

That would not have any effect on the resulting file inside the container actually, but it would make sense to mark executables as such, as a general rule.

I can combine the COPY instructions to reduce the number of layers. It reduces the number of layers, which I think helps with size (although I'm not clear on how big an impact this has).

It would not reduce the image size significantly. You spare some space if you avoid of saving intermediate files, that gets deleted or overridden/modified.

[lilatomic]

We could also change the permission of the files outside the container. thoughts?

That would not have any effect on the resulting file inside the container actually, but it would make sense to mark executables as such, as a general rule.

Are you sure about that? I tried with a simple dockerfile:

FROM	bash
COPY	a.txt .
CMD	ls -la a.txt

Changing the permissions on a.txt seems to work fine

> sudo chmod 451 a.txt
> sudo docker run -it (docker build -q .)
-r--r-x--x    1 root     root             0 May  6 00:53 a.txt
> sudo chmod 770 a.txt
> sudo docker run -it (docker build -q .)
-rwxrwx---    1 root     root             0 May  6 00:53 a.txt

The docs have this to say, buried in the COPY reference, which isn't super clear to me:

If is any other kind of file, it is copied individually along with its metadata.

[frafra]

I might be wrong or confusing with one of the various different build methods. If it works, great :)

[lilatomic]

sorry folks, are we waiting on me for something on this?