[RFE] Specify update.conf directives as annotations

[tijmenvandenbrink]

Current situation

Currently we specify the SERVER, GROUP and MACHINE_ALIAS in /etc/flatcar/update.conf when bootstrapping a node. This makes it quite static as we're not touching/actively managing this file after initial bootstrap.

Impact

At this point there is no way to manage these directives via Kubernetes which forces us to manually change it on the host.

Ideal future situation

Ideally we would be able to set annotations on a node specifying SERVER, GROUP and MACHINE_ALIAS which overrides the directives in /etc/flatcar/update.conf. This would give us a lot of flexibility in controlling which versions run within a cluster. A specific use case I see is running a small set of beta release nodes in a cluster allowing for early detection of issues.

Implementation options

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Additional information

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[invidian]

Thank you for reporting. I'll close this as duplicate of #34 since IIUC is about the same thing.