Cases1 case

1 to 1 of 1

1. IL-0168 Simultaneous cluster auto-upgrades overloaded Scaleway's Kubernetes API, and a node authentication retry loop kept Kapsule and Kosmos nodes NotReady in FR-PAR

   Scaleway2024

   Symptoms

   At 01:04 CET on 13 February 2024, the Kubernetes API behind Scaleway's managed Kubernetes services Kapsule and Kosmos in the Paris region (FR-PAR) spiked in RAM and CPU use and ran out of memory. Nodes in FR-PAR could no longer authenticate to their control plane, and some of them went "Not Ready". Customers on both shared (mutualized) and dedicated environments were affected.

   Node NotReadyControl plane lagOOMKilled

   Trigger

   A new Kubernetes release was made available to all users on 12 February 2024, and during the night of 12 to 13 February many clusters triggered their auto-upgrade at the same time.

   Root cause

   Capacity exhaustion

   Component

   Kubernetes API server

   Contributing factor

   Retry stormAutomation amplificationNo staged rollout

   Detection

   The timeline's first entry, at 01:04 CET, records the Kubernetes API's RAM and CPU spikes and out-of-memory state, with nodes unable to authenticate to their control plane and some becoming "Not Ready". The first recorded action, 42 minutes later at 01:46, was to increase the resources allocated to the API.

   Remediation

   • increased the resources allocated to the Kubernetes API at 01:46 and again at 02:20
   • applied API traffic restrictions at 02:30 to smooth the incoming traffic
   • removed the traffic restrictions progressively in 50-100 batches from 03:20
   • ran a script at 03:40 to replace the failing nodes created during the congestion
   • rolled back to the former node authentication mechanism, first on a subset of clusters from 15:45 and on all clusters by 19:41 on 19 February
   • disabled cluster upgrade and configuration update features until 10:30 on 20 February

   Action items

   • Increase the resources allocated to the Kubernetes API
   • Roll back to the former node authentication mechanism
   • Implement a local authentication cache on nodes
   • Rework the resource allocation strategy to behave better under load spikes
   • Add new request queuing mechanisms for Kubernetes
   • Separate the different components to reduce side effects under high load or failure
   • Monitor selected metrics closely to identify anomalous patterns earlier
   • Refund customers who deployed nodes during the incident but could not use them normally

   Lessons

   Letting many clusters auto-upgrade at the same moment after a release turns routine upgrades into one coordinated load spike on the shared Kubernetes API. A node authentication mechanism that retries without letting up turns a slow API into an unavailable one, and auto-healing that replaces NotReady nodes amplifies the problem. The congestion pattern had already appeared three weeks earlier, and short-term mitigations did not stop it from recurring, so Scaleway rolled back the new authentication mechanism. Scaleway notes that as the number of customer clusters and nodes grows sharply, traffic control mechanisms have to improve to prevent congestion.

   View case

By root cause1