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1. IL-0087 After a cold reboot of RKE2 nodes, pods could not get IP addresses because Multus could not reach the Kubernetes API, and further reboots spread the failure to every node

   Fyra Labs2023

   Symptoms

   At around 2 AM ICT on 2023-04-09 the team saw unusual CPU use on one cluster node, which throttled every other service on it and made them fail. They presumed an upstream container runtime bug in containerd and runc and decided to fully reboot the affected nodes, taking the cluster down for maintenance on the assumption that it was not in active use.

   Sustained high node CPUService outage

   Trigger

   A full cold reboot of the nodes that showed unusual CPU use, followed by upgrades and cold reboots of the other nodes.

   Root cause

   unknown

   Component

   Multus meta-CNICalicoContainer runtime

   Contributing factor

   Harmful manual actionUnverified assumption

   Detection

   The team saw unusual CPU use on a node around 2 AM ICT and failing services on the rebooted nodes around 2:30 ICT; developers reported the Terra repositories down at 6:31 ICT.

   Remediation

   • uninstalled Multus and Calico and replaced them with the Cilium CNI
   • rolled back most cluster settings except the CNI

   Lessons

   Rebooting nodes to clear one problem can expose another; here a CNI chain could not reach the API server after a cold start. Repeating the same reboot on more nodes while the first failure was not understood spread the outage from a few nodes to the whole cluster. The team also found that Cilium's real resource use in their cluster was acceptable, contrary to the benchmark they had relied on.

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