So it's "build on release" vs "build on runtime"? ssh-ubuntu is mostly used for CI, so startup time is crucial for dev loops. What's the startup time difference? Also if Docker layer caching helps in the runtime case, we can measure the repeat-build (warm cache) scenario.

Also paging @wyrzyk as the primary author of this module 😉

So it's "build on release" vs "build on runtime"? ssh-ubuntu is mostly used for CI, so startup time is crucial for dev loops. What's the startup time difference?

There's next to no difference - you either download the image or build it locally, so it's very similar in terms of performance.

It was optimised to build the image once and then benefit from a faster and more stable dev loop. Maybe it's possible to support both approaches? 🤔

But locally you download it once.

But locally you download it once.

And you build it only once too, all subsequent runs come from cache.

I get the build once part, caching is a feature of building itself.
But where's the upload part?

I get the build once part, caching is a feature of building itself.
But where's the upload part?

There's no upload. We don't really need to upload it.

Ok, so without upload, it will not download at all correct? I'm confused because:

you either download the image or build it locally

and

But locally you download it once.

Ok, so without upload, it will not download at all correct? I'm confused because:

you either download the image or build it locally

and

But locally you download it once.

I was talking about the data needed to build the image.

Ok, so it's clear.
Before: download final image
After: download dependencies + build final image

So "after" could be slower than "before", that's why I asked for the difference.
You said:

There's next to no difference - you either download the image or build it locally, so it's very similar in terms of performance.

Was it assumed or tested?