Add proposal for an optional preflight check in kapp for validating safety of CRD upgrades

[everettraven]

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[everettraven]

Note: I will squash all the commits once this is in an approved state and ready to merge.

[mamachanko]

[thought, non-blocking]: Have you considered use-cases where the CRD author/user would like to control the behaviour from the annotations on the CRD itself, say to bypass them all? Following the precedence of kapp's configuration and annotations I think one could argue for both. Maybe annotations are a potential footgun.

[everettraven]

[thought, non-blocking]: Have you considered use-cases where the CRD author/user would like to control the behaviour from the annotations on the CRD itself, say to bypass them all? Following the precedence of kapp's configuration and annotations I think one could argue for both. Maybe annotations are a potential footgun.

@mamachanko Are you referring to a case where a user wants the preflight check enabled, but wants to ignore a specific CRD or which validations to run against a CRD?

[mamachanko]

[thought, non-blocking]: Have you considered use-cases where the CRD author/user would like to control the behaviour from the annotations on the CRD itself, say to bypass them all? Following the precedence of kapp's configuration and annotations I think one could argue for both. Maybe annotations are a potential footgun.

@mamachanko Are you referring to a case where a user wants the preflight check enabled, but wants to ignore a specific CRD or which validations to run against a CRD?

Exactly.

[everettraven]

[thought, non-blocking]: Have you considered use-cases where the CRD author/user would like to control the behaviour from the annotations on the CRD itself, say to bypass them all? Following the precedence of kapp's configuration and annotations I think one could argue for both. Maybe annotations are a potential footgun.

@mamachanko Are you referring to a case where a user wants the preflight check enabled, but wants to ignore a specific CRD or which validations to run against a CRD?

Exactly.

So for ignoring a specific CRD, I don't think that is unreasonable but IMO isn't necessary for the base implementation and is something that can be added in the future.

For annotations regarding what validations to run against the CRD, I think that is a bit more nuanced and likely opens up for a wealth of footguns. I think if there is a strong use case for that then I don't see why it couldn't be added, but I think for the initial implementation it makes the most sense to have either all the validations run or none of them (i.e check is enabled/disabled).

[praveenrewar]

Thank you so much @everettraven for all that you have been doing to improve kapp ❤️
The proposal looks good to me.

Adding some thoughts as a side note for future: preflight checks might open up another realm (of templating and overlaying) for kapp which might fall outside it's philosophy of deploying and managing applications on kubernetes, so we need to be cautious about what we choose to configure using preflight checks.

[tmshort]

Is this ready to merge?

[everettraven]

Is this ready to merge?

I believe this has now passed the lazy consensus period. I think it is good to merge.

cc @praveenrewar

[joaopapereira]

Please change the status to Approved in a separate commit and we will be able to merge it

[everettraven]

@joaopapereira should be done now in 1d187a5

[joaopapereira]

Approved after discussion in Community Meeting and Lazy consensus vote