Cases2 cases

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1. IL-0099 User servers on 2i2c's Earthscope hub took over 15 minutes to start and kernels were killed during a workshop, because a profile option guaranteed 8 GB of memory with no limit on 32 GB nodes

   2i2c2025

   Symptoms

   On 12 May 2025 at 20:15 EEST a Freshdesk ticket reported that users' servers on the Earthscope hub were taking more than 15 minutes to start and that their kernels were being killed. It happened during a workshop and also affected other instructors using the hub; a second report said a short course of about 30 users was having major problems.

   Pod eviction

   Trigger

   A workshop with about 30 users on a profile option that guaranteed 8 GB of memory and set no memory limit on 32 GB nodes.

   Root cause

   Capacity exhaustion

   Component

   Container memory limitNode pool

   Contributing factor

   No resource requests or limits

   Detection

   A Freshdesk support ticket from the community at 20:15 EEST, brought to the team's attention in the #support-freshdesk Slack channel at 20:49.

   Remediation

   • ran a helm rollout and hub redeploy, which partly improved server starts
   • made the 'medium' profile available and raised its memory guarantee to reduce overcommitment
   • pre-warmed the cluster with 15 nodes for the 30-user workshop
   • set explicit memory limits, with the guarantee equal to the limit, on the community's small-node profile options (https://github.com/2i2c-org/infrastructure/pull/6047)

   Action items

   • Write an incident report
   • Hold an internal retrospective about the incident (https://github.com/2i2c-org/meta/issues/2194)

   Lessons

   A memory guarantee without a limit lets a user server grow into memory that other pods on the same node were counting on, and on a shared node that ends with users' pods evicting each other. Setting the guarantee equal to the limit removes the overcommitment. For a known workshop, pre-warming enough nodes ahead of time keeps server start times short.

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2. IL-0070 Critical pods on core nodes evicted when Prometheus began scraping about 200 nodes after a dask-gateway scale-up

   2i2c2023

   Symptoms

   The hub pod of the prod JupyterHub on the leap cluster (leap.2i2c.org) restarted unexpectedly during a large node scale-up, and a user opened a support ticket. The ingress-nginx and proxy pods kept running.

   Pod evictionPods Pending

   Trigger

   A user's dask-gateway workload added about 100 dask-worker nodes within a minute, and Prometheus started scraping the metrics exporters on about 200 nodes.

   Root cause

   Capacity exhaustion

   Component

   PrometheusNode pool

   Contributing factor

   No headroomExcessive blast radiusMonitoring blind spot

   Detection

   A user support ticket (2i2c Freshdesk ticket 414) about the leap hub; the engineer then looked at Grafana and the cluster's nodes and events.

   Action items

   • Configure CPU and memory requests for the hub and proxy pods (#2127; at least 100m CPU was proposed)
   • Make the Grafana OOMKiller dashboard work (#2213)
   • Move LEAP cloud infrastructure to shared nodes (#2209)
   • Update resource requests and limits, mainly for ingress-nginx and Prometheus (#2324)
   • Decide whether Prometheus should scrape dask worker pods (#2366)

   Lessons

   Prometheus load grows with the number of nodes, so a burst of autoscaled nodes can push a nearly full core node over the edge and evict the pods that matter most. Core pods that request 10m of CPU get a tenth of the CPU share of busy neighbours that request 100m. Kubernetes events expire after an hour, so evidence of OOM kills needs a dashboard that keeps it.

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