Investigate the use of uncached and cached clients in KubeadmControlplane

[sedefsavas]

This issue is to investigate possible problems that may happen due to the usage of cached client in KubeadmControlplane. In a CPU restricted management cluster cache may become out-of-date. Since KCP is a critical part in the sense that control plane health relies on its correctness, although cached calls are cheaper, we may want to switch back to using uncached clients and read from api server directly.

Couple of places we may want to use uncached client where we get Machines is reconcileHealth and reconcileDelete:

cluster-api/controlplane/kubeadm/internal/cluster.go

Line 203 in a82cfd9

machines, err := m.GetMachinesForCluster(ctx, clusterKey, machinefilters.ControlPlaneMachines(clusterKey.Name))

cluster-api/controlplane/kubeadm/controllers/controller.go

Line 382 in a82cfd9

allMachines, err := r.managementCluster.GetMachinesForCluster(ctx, util.ObjectKey(cluster))

Another option would be to use the same Machine list we get at the beginning of the reconcile and do not make get Machines call anywhere else in KCP to avoid any inconsistency in the list we use to decide scale up/down.

Related PR: #3759

[vincepri]

/milestone v0.4.0
/help

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[fabriziopandini]

/area control-plane

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[fabriziopandini]

/kind design

[vincepri]

/milestone v0.4.x

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/close

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@fejta-bot: Closing this issue.

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