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1. IL-0097 A cluster autoscaler version bump was incompatible with the one cluster still on Kubernetes 1.33, so no scale-up events fired and new nodes were not created

   2i2c2026

   Symptoms

   At 15:10 (Bucharest time) on 2026-03-31 an alert fired for the prod hub on the berkeley-geojupyter cluster on AWS: "[FIRING:1] At least two servers failed to start in the last 30m cluster=berkeley-geojupyter hub=prod (provider=aws immediate action needed)". It opened PagerDuty incident #2057.

   Scale-up failure

   Trigger

   An upgrade merged on 2026-03-30 bumped the cluster autoscaler version, and the new version was incompatible with Kubernetes 1.33, which the berkeley-geojupyter cluster still ran.

   Root cause

   Breaking change in an upgrade

   Component

   Cluster autoscaler

   Contributing factor

   Deferred upgradesUnverified assumption

   Detection

   An alert that at least two servers failed to start in the last 30 minutes fired at 15:10 and opened PagerDuty incident #2057. The report notes it was triggered by an automatic health check run, not by users being unable to start servers.

   Remediation

   • upgraded the cluster's Kubernetes version from 1.33 to 1.34
   • downgraded the cluster autoscaler by one patch version to 9.55.0, the version meant for Kubernetes 1.34

   Action items

   • The change in https://github.com/2i2c-org/infrastructure/pull/8008 (the report gives only the link)
   • Use recurrent issues, such as the recurrent-k8s-aws-upgrades workflow, to standardize Kubernetes versions across clusters

   Lessons

   Because the context of the autoscaler bump was fresh, the team went down the right path from the start. The upgrade batches had been designed with only 1.32 clusters in mind, so the one 1.33 cluster was missed and got an incompatible autoscaler. 2i2c notes it was lucky that an automatic health check, not real users, hit the failure first.

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