Kubernetes RBAC: Fix ServiceAccount Authorization Failures Triggered by Resource Exhaustion (OOM/CPU)
Quick Fix Summary
TL;DRScale up the failing pod's resource limits and restart it.
When a pod (especially kube-apiserver or a critical service mesh sidecar) is killed due to OOM or throttled due to CPU exhaustion, it may fail to perform RBAC checks, causing cascading 'Authorization Failed' errors for ServiceAccounts across the cluster.
Diagnosis & Causes
Recovery Steps
Step 1: Verify Resource Exhaustion and Identify the Failing Component
Check for OOMKilled or CPU-throttled pods, focusing on system components. Use kubectl describe and kubectl top.
kubectl get pods -n kube-system --field-selector=status.phase!=Running
kubectl describe pod -n kube-system <pod-name> | grep -A 5 -B 5 "OOMKilled\|Terminated"
kubectl top pods -n kube-systemStep 2: Immediately Scale Up the Affected Pod's Resources
If kube-apiserver is affected, patch its deployment with higher limits for immediate relief.
kubectl patch deployment -n kube-system kube-apiserver --type='json' -p='[{"op": "replace", "path": "/spec/template/spec/containers/0/resources/limits", "value": {"cpu": "2", "memory": "4Gi"}}]'Step 3: Check API Server and Kubelet Logs for Authorization Errors
Examine logs to confirm the link between resource pressure and RBAC failures.
kubectl logs -n kube-system <kube-apiserver-pod-name> --tail=100 | grep -i "authorization\|oom\|thrott"
journalctl -u kubelet --no-pager | tail -100 | grep -i "authorization"Step 4: Analyze RBAC Request Load with Metrics Server/API Priority & Fairness
Check if a specific ServiceAccount or namespace is generating excessive LIST/WATCH requests.
kubectl get --raw /metrics | grep "apiserver_flowcontrol"
kubectl get --raw /metrics | grep "apiserver_request_total" | grep "resource=\"*\""Step 5: Restart the Failing Pod to Clear Corrupted State
Force a restart of the resource-exhausted pod after adjusting limits.
kubectl delete pod -n kube-system <pod-name>Step 6: Apply Correct Resource Limits and Requests Permanently
Update the manifest (Deployment/DaemonSet) for the affected component with sustainable values.
kubectl edit deployment -n kube-system kube-apiserver
# In the editor, locate the 'resources' block and adjust. Example:
resources:
requests:
cpu: "1"
memory: "2Gi"
limits:
cpu: "3"
memory: "6Gi"Step 7: Review and Optimize Client Queries
Identify clients performing inefficient LIST calls (e.g., missing label selectors) and enforce best practices.
# Audit frequent requestors. This requires cluster auditing enabled.
# Check for pods with high API call rates via sidecar metrics or client-side logging.Architect's Pro Tip
"This often happens during a cluster-wide deployment that triggers thousands of pods to resync their informers simultaneously, overwhelming the API server's memory. Check for deployments using default, unoptimized Kubernetes client-go configurations."
Frequently Asked Questions
Why does resource exhaustion cause RBAC failures?
The kube-apiserver process, which evaluates RBAC rules, becomes unresponsive or is killed. Requests from ServiceAccounts then time out or are rejected, appearing as authorization failures even if the RBAC rules are correct.
My pod has 'OOMKilled' but my application logs show 'RBAC Authorization Failed'. Which is the real error?
OOMKilled is the root cause. The RBAC error is a symptom. The pod's process died mid-request, leaving clients with a failed authorization response. Always treat OOMKilled as the primary issue.