Cases3 cases

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1. IL-0171 Karpenter node auto-repair replaced EKS GPU nodes about 10 minutes after they became Ready, in a loop, because the Bottlerocket NVIDIA AMI lacked libdcgm.so and set AcceleratedHardwareReady to False

   Inflab2025

   Symptoms

   GPU nodes for an AI video upscaling job were created normally and reached Ready, and then about 10 to 11 minutes later Karpenter treated each one as unhealthy and replaced it. Every new node went the same way, so the GPU pods kept restarting and the upscaling work could not make progress.

   Node recreation loopGPU unavailable

   Trigger

   Enabling Karpenter's node auto-repair feature gate (nodeRepair: true) and then running GPU pods on nodes from the Bottlerocket NVIDIA AMI.

   Root cause

   Software defect

   Component

   KarpenterNode operating system imageGPU driver

   Contributing factor

   Automation amplificationUnverified assumption

   Detection

   The team noticed GPU nodes being replaced repeatedly after running GPU pods, then found the DCGMError message in the node events.

   Remediation

   • Disabled Karpenter node auto-repair by setting the nodeRepair feature gate to false

   Lessons

   Automatic node repair acts on every unhealthy node condition, including AcceleratedHardwareReady, so an image defect that only breaks GPU health monitoring is enough to have every GPU node terminated and recreated in a loop. Before turning on auto-repair, check which conditions it watches and whether the node image reports them correctly. Disabling auto-repair stops the loop at once but is only a temporary measure; installing the missing library or changing the AMI address the cause but cost more on an immutable OS such as Bottlerocket.

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2. IL-0007 The AWS VPC CNI could not assign IP addresses to pods as an EKS cluster ran out of IPv4 space

   Adevinta2024

   Symptoms

   One evening the platform team that runs SCHIP, Adevinta's internal runtime platform on Kubernetes, was paged because some DaemonSets were failing. Checking the pod status showed this error from the network plugin: name="aws-cni" failed (add): add cmd: failed to assign an IP address to container

   IP address exhaustionPods Pending

   Trigger

   Not stated for the first page. It came in June, during the migration from SCHIP's kube-aws-based clusters to EKS-based clusters; the write-up mentions spikes of pods, such as a job that goes rogue or failing jobs that keep their IPs, as ways a cluster can run out.

   Root cause

   Capacity exhaustion

   Component

   AWS VPC CNIVPC subnet or pod address rangeKarpenter

   Contributing factor

   Unreviewed defaultsNo capacity planning

   Detection

   A pager alert that some DaemonSets were failing. The on-call engineer checked the pod status and found the aws-cni error about failing to assign an IP address.

   Remediation

   • Rolled out VPC CNI custom networking with a secondary CIDR to the smaller clusters from late August
   • Paused the EKS migration in September while available IPs were very low
   • Rolled out custom networking to the rest of the fleet
   • Added the --reserved-enis parameter to the Karpenter deployment

   Action items

   • Use VPC CNI custom networking with a secondary CIDR across the whole fleet
   • Make Karpenter account for custom networking with the --reserved-enis parameter

   Lessons

   For a platform team, the VPC CNI is not ready to scale in production without time spent on capacity planning, and every option has its pros and cons. For large clusters started today, IPv6 is the cheaper and more future-proof option. Do not assume that what works in small clusters will keep working when they grow.

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3. IL-0182 Too few CoreDNS replicas on EKS were overloaded during traffic spikes, raising latency and cutting the network for task pods, and the over-provisioned, tightly spread CoreDNS pods added later blocked Karpenter consolidation

   이언철2024

   Symptoms

   When traffic changed sharply, CoreDNS came under heavy load, and the cluster saw network problems and a sudden rise in latency. The horizontal pod autoscaler then added pods, database connections surged, and the impact spread to the whole service.

   High latencyIntermittent connection failuresAutoscaler misbehaviour

   Trigger

   Sharp changes in traffic loaded the small number of CoreDNS pods beyond what they could handle.

   Root cause

   Capacity exhaustion

   Component

   CoreDNSKarpenterHorizontal pod autoscalerPod scheduling and placement

   Contributing factor

   Automation amplificationHarmful manual action

   Remediation

   • Set up the Cluster Proportional Autoscaler for CoreDNS with nodesPerReplica and coresPerReplica chosen for the instance types in use
   • Spread CoreDNS with soft topologySpreadConstraints (ScheduleAnyway) instead of anti-affinity so Karpenter could consolidate nodes
   • Added alert thresholds on CoreDNS error rate, panics, request duration and request rate
   • Deployed NodeLocal DNSCache so each node answers DNS from a local cache and forwards misses to the main CoreDNS

   Lessons

   A fixed, small number of CoreDNS pods cannot follow a cluster whose nodes and pods change quickly with traffic, and the damage spreads: DNS latency triggers autoscaling, which in turn floods the database with connections. Simply adding many CoreDNS replicas created a different problem, because with tainted nodes and a maxSkew: 1 spread constraint the pods piled onto a few nodes and blocked Karpenter consolidation. Scaling CoreDNS in proportion to the cluster and putting a DNS cache on every node handled both.

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