Add support for ignition instance initialization system

[gabriel-samfira]

/kind feature

This feature request was prompted by #15385. There are a number of container oriented Linux distributions that currently use ignition instead of cloud-init to perform instance initialization on first boot.

Some of the distributions currently using ignition:

• Fedora CoreOS
• RHEL CoreOS
• Flatcar Linux

Flatcar also has a "compatibility layer" via coreos-cloudinit, but the native way to configure it is via ignition.

Ignition uses a json configuration file. The spec for the ignition config can be found here: https://github.com/coreos/ignition/blob/main/docs/specs.md . It runs during first boot, from initramfs and configures the system before it pivots to the real rootfs and continues the boot process.

More details in regards to how it works can be found here: https://github.com/coreos/ignition/blob/main/docs/getting-started.md

Proposed change

It would be great to have an additional flag that would prompt kops to generate a valid ignition user-data, that would accomplish the same goal as the cloud-init user-data. This would allow users to opt for any of the existing container focused distributions that make use of ignition, as well as any other future distros that may opt to use ignition instead of cloud-init.

[gabriel-samfira]

Cross link to the Flatcar feature request: flatcar/Flatcar#1029

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/lifecycle stale

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/lifecycle rotten

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/close not-planned

[k8s-ci-robot]

@k8s-triage-robot: Closing this issue, marking it as "Not Planned".

In response to this:

The Kubernetes project currently lacks enough active contributors to adequately respond to all issues and PRs.

This bot triages issues according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
• After 30d of inactivity since lifecycle/rotten was applied, the issue is closed

You can:

• Reopen this issue with /reopen
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/close not-planned

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