Cases36 cases

9 to 13 of 36

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-0078 Enabling EKS secrets encryption with KMS through Terraform removed worker node IAM permissions and took down all ZenML Pro workspaces

   ZenML2025

   Symptoms

   Between 12 AM and 8 AM CEST on 11 May 2025, every ZenML Pro workspace server was unreachable, so customers could not use workspace UIs or pipelines. The ZenML Pro dashboard was not affected.

   Service outage

   Trigger

   At 23:38 on 10 May, secrets encryption with AWS KMS was enabled through Terraform as part of the EKS module upgrade.

   Root cause

   Software defect

   Component

   TerraformNode pool

   Contributing factor

   Unrepresentative stagingDeferred upgrades

   Detection

   Engineers found the cluster degraded when they resumed the upgrade at 06:00.

   Remediation

   • deleted and recreated the EKS node group with the correct IAM permissions and configuration
   • restored service access across all affected ZenML Pro environments

   Action items

   • Upgrade all Terraform modules (EKS, VPC) to current supported versions
   • Complete the EKS cluster upgrades as planned
   • Review the strategy for periodic Kubernetes and infrastructure upgrades to prevent a recurrence

   Lessons

   A successful upgrade on a much smaller staging cluster understated the risk of the same change in production. Skipping Kubernetes and module versions let upgrade complexity build up until one upgrade carried many changes at once.

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3. IL-0027 All CoreDNS pods landed on one node, the node ran out of memory, and DNS for the whole service went down

   Backpackr2025

   Symptoms

   Services on the production Amazon EKS cluster behind the idus marketplace threw intermittent errors whose cause was hard to pin down. Calls to external services such as RDS and Redis failed now and then, and whenever DNS traffic spiked, domain lookups answered slowly or failed outright.

   DNS resolution failuresIntermittent connection failuresHigh latencyOOMKilledService outage

   Trigger

   All CoreDNS pods were scheduled onto the same node, and that node's memory usage spiked until it ran out of memory.

   Root cause

   Capacity exhaustion

   Component

   CoreDNSClient-side DNS resolver and cachekubeletContainer memory limitNode pool

   Contributing factor

   Unreviewed defaultsSingle point of failureNo caching

   Detection

   The write-up does not say how the full outage was noticed. The earlier DNS trouble showed up as intermittent service errors, and investigating failed calls to RDS and Redis led to DNS resolution failures.

   Remediation

   • deployed NodeLocal DNSCache as a DaemonSet in front of CoreDNS
   • added a PodDisruptionBudget (maxUnavailable 1) and topologySpreadConstraints across zones for CoreDNS
   • lowered ndots from 5 to 2 with dnsConfig in the Deployments

   Lessons

   The CoreDNS setup that EKS creates by default (two pods) can be enough for a small or development cluster but becomes a bottleneck in a large production cluster, and DNS is a single point of failure that needs high availability and room to scale. Tuning the CoreDNS cache and buffer size only relieved the symptoms; the real load came from the extra queries that ndots:5 generates for external names. A CoreDNS pod without a memory limit can share a node's fate with everything else on it.

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4. IL-0020 During an EKS 1.30 upgrade the descheduler tried to reschedule every pod on the cordoned nodes at once and production workloads went down

   UK Ministry of Justice2025

   Symptoms

   At 09:36 on 18 March 2025, during the upgrade of the live cluster to EKS 1.30, users reported that their pods were being terminated and were not restarting automatically, in both production and non-production environments. Automated infrastructure alerts fired as well, and production services had outages.

   Pod evictionPods PendingService outageUpgrade stall

   Trigger

   Upgrading the live EKS cluster from 1.29 to 1.30, during which the descheduler attempted to reschedule all pods on the cordoned nodes simultaneously.

   Root cause

   Faulty deployment

   Component

   DeschedulerNode poolCluster autoscaler

   Contributing factor

   No headroomNo alert on limitUnreviewed defaults

   Detection

   Users reported at 09:36 that pods were being terminated and not restarting, and automated infrastructure alerts fired.

   Remediation

   • Removed the cordon annotation so pods could be rescheduled
   • Deleted stuck 1.30 nodes to force their recreation
   • Added a new node group of 20 nodes running 1.30 by hand
   • Cordoned and drained all old 1.29 nodes onto the new 1.30 nodes

   Action items

   • Raise an AWS Production System Down support case (Case ID: 174229643100496)
   • Get guidance from AWS support on querying control-plane logs to find the root cause of similar issues
   • Document a runbook for emergency scaling of a new node group in case of unexpected capacity shortages
   • Alert on an imbalance between the autoscaling group and the Kubernetes nodes
   • Review the descheduler configuration to understand why it throws pods off cordoned nodes, and fix it where possible
   • Alert on spikes in the pending pod count

   Lessons

   The write-up lists review actions rather than lessons. They show the team had no documented way to add an emergency node group, no alert on a mismatch between the autoscaling group and the nodes Kubernetes sees, no alert on a spike in pending pods, and no clear understanding of how the descheduler treats cordoned nodes.

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5. IL-0161 A faulty earlier API update made new LKE cluster provisioning in Toronto time out for three days, leaving clusters with no node pools or the wrong number of nodes

   Linode2024

   Symptoms

   At about 14:05 UTC on 22 April 2024, Linode's team noticed that new LKE clusters were failing to provision in the Toronto data center.

   Cluster or node provisioning stallIntermittent timeouts

   Trigger

   A previous update to the API did not work as intended and caused timeouts when new LKE clusters were provisioned.

   Root cause

   Software defect

   Component

   Node pool

   Contributing factor

   –

   Detection

   Linode's team noticed new LKE clusters failing to provision in the Toronto data center at about 14:05 UTC on 22 April 2024.

   Remediation

   • disabled the affected section of Toronto infrastructure from provisioning new LKE clusters
   • implemented a fix for the faulty API update
   • put the disabled infrastructure back into use after the fix

   Lessons

   The fault was in an earlier API change, not in the infrastructure that showed it, but most failures concentrated on one backend resource in one data center. Taking that resource out of provisioning limited the impact while the root cause was found, which took three days.

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