I don't know any scenario where I'd need any of that, but I love such things regardless.

About git.kontain.me - what if I'd like to setup my own copy of such a service and would like it to work with a non-public git repo, how to pass credentials? Since you support only cloning over https (btw, why not over ssh as well?) - one could use an URL of format user:pass@host:port/path/to/repo, would that work?

I sometimes wonder why there aren't more bespoke container tools (like yours). Would people be willing to pay for stuff like what you have built, if someone took the time to "productionize" it? Or is there no market?

I can't imagine this happening in reality (i.e. people wanting to do this for normal production applications), but after reading your comment I must admit I am very tempted to try it for purely esoteric reasons.

And uses SOAP for identity and authorization.

An image is immutable, many Dockerfiles are not idempotent. Running them multiple times at different times can lead to different results easily.

Building every time takes a lot of time. Both on download and execution time.

Also when building an image you may need to have access to resources that are unavailable where you actually want to run the image. So I see definitely reason for both to exist.

Or am I misunderstanding your point?

You absolutely can just build things and put them on base images without building or pulling the base image at any point. This is a central feature of ko, a simple container build tool for most Go applications: https://ko.build

(I am a maintainer)

There are many ways to achieve this. If you are just copying artifacts, and not using RUN, then there is in principle no need to download the base image at all. Feel free to message me if you'd like to chat (email is in my profile).

You can, by using FUSE and lazy pulling files as they are opened. I'm working on doing this, myself.

I'd say the limitations are relative to your use case: `docker build` works well enough in most cases, but sometimes it's not the right tool for the job (e.g., you cannot use `docker build` inside an AWS Lambda, you can get way better performance from specialized tools in some cases [1], etc)

[1]: see my sibling comment at https://news.ycombinator.com/item?id=48301041

Creating multi arch builds for starters. Maybe creating image from just composing layers instead of “running” a Dockerfile? The first I find cumbersome and is easily overcome by using buildx.

I haven’t tried lately, but I think running a build still requires running a docker engine. Buildx has builders that run as containers.

The idea is that, in many cases, you can create a layer "by hand" without running actual Linux programs. Layers don't need to be pre-existing, the only requirement is that they can be built programmatically (inside the browser, in this case). The demo actually does that: it "manually" creates a layer from the user-specified entrypoint script, then creates an image from the pre-existing base image's layers and the new entrypoint layer.

In a more real scenario, you can e.g., turn pip wheels into layers without actually using docker's RUN command. All it takes is to massage the data from one archive format into another, programmatically. This unlocks lots of potential (e.g., it becomes embarrassingly parallel to build a container image comprised of pip wheels). Combine that with a good layer caching strategy and a registry that takes advantage of it, and you can have near-instant container builds for arbitrary sets of pip dependencies.