📖 book: add ipam contract

[schrej]

What this PR does / why we need it:
Adds the IPAM contract to the book.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):

/area ipam
/area documentation

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/lifecycle stale

[sbueringer]

@schrej Still interested in this one?

[schrej]

Yes, just forgot about it... I think I put it on hold due to some uncertainty with regards to clusterctl move. And now I also need to update regarding spec.clusterName instead of the annotation.

[schrej]

/remove-lifecycle stale

[enxebre]

@schrej is this still wip? lgtm as good starting point

[sbueringer]

@schrej friendly reminder 😀

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[schrej]

I think this should be ready now. I've updated it to include the new spec.clusterName field and noted that the cluster name label is deprecated.

Sorry that it took so long.

[sbueringer]

@lubronzhan Do you maybe have some time to take a first look? (in case you're familiar with what we did in CAPV at the time)

[lubronzhan]

Sorry for the late reply. Overall LGTM!

[sbueringer]

Thx! Just a few small findings.

[sbueringer]

What about controller / blockOwnerDeletion here?

[schrej]

Good point. We're currently investigating an issue when deleting metal3 based clusters where claims are deadlocked due to the cluster vanishing before they are cleaned up. The paused check prevents the claim from being released if the cluster can't be found. We'll either have to make sure that the cluster doesn't get deleted, or ignore the paused check when releasing addresses.

[schrej]

I propose to merge this as is, and we'll update it if we change how this works in the in-cluster ipam implementation.
I've added a note to the ipam issue: kubernetes-sigs/cluster-api-ipam-provider-in-cluster#289

[fabriziopandini]

Nice!
Happy to lgtm/approve once findings are addressed

[k8s-ci-robot]

PR needs rebase.

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