Make host information available in templates

[prskr]

Description

Hi all,

thanks for this awesome tool!

To give a little bit of context first: I'm using lima to provision CI agents on my MacStudio and my Linux desktop.
I'm using the same template for both machines, because the CI agent should have the same capabilities for both systems, the main difference is that the Mac runs on a ARM64 architecture and the Linux on desktop x86_64 architecture.

I saw, that there is already an issue ( #3993 ) that goes into a similar direction, that it would be great to be able to query certain driver/host facts in a template, to be able to switch certain behavior.

I propose to go one step further and not only expose certain driver features but also

• OS
• architecture
• CPU core count
• Total memory in MB
• hostname
• ???

via something like {{ .host.<fact> }}

This would make it a lot easier to dynamically adapt the template to the host.

The challenges I'm currently facing are:

• on Linux I need to fallback to legacy BIOS
• scripts to install software have to check for the host CPU architecture and incorporate the current architecture in the URL
• depending on the host, I've to reduce the size (CPU cores and memory) of the VM
• probably I'm forgetting something 😅

If that is something you would consider I'd be happy to also create a PR for it of course :)

[AkihiroSuda]

on Linux I need to fallback to legacy BIOS

Why?

scripts to install software have to check for the host CPU architecture and incorporate the current architecture in the URL

You can check $(uname -m)

[prskr]

Regarding the legacy fallback: not entirely sure, might have been an issue with my QEMU setup on Arch Linux or something in Rocky or Alma Linux. To be honest, I did quite a lot experimenting until I found a combination that worked.

As for uname -m or also dpkg --print-architecture, I am aware that this is possible and I used that to work around it, but it depends on guest OS, so I can't for instance copy files depending on the guest OS architecture from the host. At least I can't think of something easy.

In the end, the idea is, to offer template authors more flexibility when it comes to environment specific customizations.

EDIT: to probably better explain what I mean: as initially mentioned I have some Forgejo Runner instances on my private machines. The machines differ in architecture (on purpose) and apart from what I mentioned already, I also had to have different configuration files depending on the guest OS architecture because of different runner labels, different container images that should be used and the like.

While it is perfectly possible to use uname -m to conditionally fetch this or that binary from Github releases it is not that easy to update configuration files in the same way. Usually you end up with something like sed calls or gomplate or envsubst or anything like that. Just to mention another use case where advanced templating capabilities would be helpful