Quadlet - single file specification

[apparle]

Feature request description

For a multi-container, multi-volume service, there's no easy way to capture the specification in a single place -- I've to create separate container files, pod files, network files, volume files etc. There's kube files but they also cannot contain everything and have their own specification. This makes maintenance as well as sharing an installation spec for any project a complete headache because there's no single file to capture all the information about a service. Further, it's especially jarring when migrating to quadlet from docker compose, which is the most widepread format.

Since quadlets generate the corresponding unit files, it can very well digest a single file that contains the whole spec for a particular service with all its parts -- maybe in the pod file itself, or a new .quad format or similar.

Suggest potential solution

Ideal solution - a new file format which is 1 single file with all spec associated with the service -- it's volumes, containers, networks all in 1 place. It can be a brand-new file format with YAML like indented file-format; or it can be the pod file itself, with all associated container, volume, network files concatenated, and each sub-section (eg:[Container]) specifying that part.
Either of these work, but quadlets need to improve the input specification in a way that's easier to share, deploy, maintain.

Have you considered any alternatives?

A clear and concise description of any alternative solutions or features you've considered.

Additional context

Add any other context or screenshots about the feature request here.

[Luap99]

The reason we have multiple files is because each file corresponds to one systemd service.

Changing that makes the design much more problematic IMO as you loose that one to one mapping. And defining yet another newly invented syntax is not going to improve the situation as you now invented several competing quadlet formats which makes everything much more confusing and harder to maintain.

I also don't really buy that a single file makes it easier to deploy. The vast majority of applications will require additional data such as config files or some shared state. So in many cases just copying a single file is not good enough anyway.

So overall I am strictly against yet another file format but I leave it open in case other maintainers think otherwise.

[apparle]

several competing quadlet formats which makes everything much more confusing and harder to maintain.

It doesn't have to be a different format -- it can be the exact same specification for [Volume], [Container], [Network] just allow them to be specified in the same file, with some sort of a de-limiter for this purpose. And since it's a quadlet translation layer, nothing necessitates it to be a 1 to 1 mapping.

I also don't really buy that a single file makes it easier to deploy.

I think you're underestimating the value of this. Yes, most projects have their own configuration files, but all of them start with "download this docker compose" or copy below code blob for docker compose; and then create a conf which has good defaults OR just use the web GUI for all the configuration. They don't describe the install set up as "copy these N files" or clone this git repo containing all these files and install them into systemd directory one by one.
The very reason docker compose is as successful as it is, is due to the ease with which it's setup can be passed on from one user to another. And I think podman needs a similarly portable and powerful mechanism to represent full set up.