Unattended Upgrades will cause AKS Engine clusters to break

[bridgetkromhout]

If using AKS Engine with unattended upgrades (such as with kured if you do not have Pod Disruption Budgets protecting your workload), Azure CNI with older Ubuntu will not be able to launch new nodes, and clusters will break if nodes need to be rebooted. See Azure/azure-container-networking#2156 for details.

To mitigate this issue, turn off kured and/or unattended upgrades: https://github.com/Azure/aks-engine/blob/master/docs/howto/troubleshooting.md#prevent-unattended-upgrades

Update Sept 7, 2023 confirmed by @CecileRobertMichon: This issue is fixed in the latest version of Azure CNI, so you will need to ensure you are using AKS Engine release 0.79.0 to prevent this problem.

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