kubernetes-debugging

name	kubernetes-debugging
description	Inspect pod logs, analyze resource quotas, trace network policies, check deployment rollout status, and run cluster health checks for Kubernetes. Use this skill when diagnosing Kubernetes cluster issues, debugging failing pods, investigating network connectivity problems, analyzing resource usage, troubleshooting deployments, or performing cluster health checks.

Kubernetes Debugging Skill

Quick Diagnostic Patterns

Pod Not Starting

# Quick assessment
kubectl get pod <pod-name> -n <namespace>
kubectl describe pod <pod-name> -n <namespace>  # Events section is key

# Detailed diagnostics
python3 scripts/pod_diagnostics.py <pod-name> -n <namespace>

# Check previous logs if CrashLoopBackOff
kubectl logs <pod-name> -n <namespace> --previous

Service Connectivity Issues

# Verify service endpoints match pod IPs
kubectl get svc <service-name> -n <namespace>
kubectl get endpoints <service-name> -n <namespace>

# Network diagnostics
./scripts/network_debug.sh <namespace> <pod-name>

# Test from debug pod
kubectl run tmp-shell --rm -i --tty --image nicolaka/netshoot -- /bin/bash

Performance Degradation

# Resource usage by container
kubectl top pods -n <namespace> --containers

# Check for OOMKilled
kubectl get pod <pod-name> -n <namespace> -o yaml | grep -A 10 lastState

# Review recent logs
kubectl logs <pod-name> -n <namespace> --tail=100 --timestamps

Cluster Health Check

# Comprehensive health report
./scripts/cluster_health.sh > cluster-health-$(date +%Y%m%d-%H%M%S).txt

Key Debugging Commands

Focus on non-obvious flags and patterns most useful during debugging:

Pod Debugging

# Cross-namespace pod overview
kubectl get pods -A -o wide --field-selector=status.phase!=Running

# Previous container logs (post-crash)
kubectl logs <pod-name> -n <namespace> --previous

# Multi-container pod: target specific container
kubectl logs <pod-name> -n <namespace> -c <container>

# Stream logs with timestamps
kubectl logs <pod-name> -n <namespace> -f --timestamps

# Describe for Events section — most useful first stop
kubectl describe pod <pod-name> -n <namespace>

# Full pod YAML including status conditions
kubectl get pod <pod-name> -n <namespace> -o yaml

Service and Network Debugging

# Confirm endpoint IPs match running pod IPs (label selector mismatch shows empty)
kubectl get endpoints <service-name> -n <namespace>

# Test DNS from within the cluster
kubectl exec <pod-name> -n <namespace> -- nslookup kubernetes.default

# Sort events by time to find recent failures
kubectl get events -n <namespace> --sort-by='.lastTimestamp'

Resource Monitoring

# Per-container resource usage (reveals which container is the culprit)
kubectl top pod <pod-name> -n <namespace> --containers

# Resource quota consumption vs. limits
kubectl describe resourcequota -n <namespace>

Emergency Operations

⚠️ These commands are destructive or disruptive. Follow the verification steps before and after each operation.

Restart Deployment

# Verify current rollout state first
kubectl rollout status deployment/<name> -n <namespace>

# Restart
kubectl rollout restart deployment/<name> -n <namespace>

# Verify rollout completes successfully
kubectl rollout status deployment/<name> -n <namespace> --timeout=120s

Rollback Deployment

# Check rollout history to pick the correct revision
kubectl rollout history deployment/<name> -n <namespace>

# Rollback to previous revision
kubectl rollout undo deployment/<name> -n <namespace>

# Confirm rollback success and pods are running
kubectl rollout status deployment/<name> -n <namespace>
kubectl get pods -n <namespace> -l app=<name>

Force Delete Stuck Pod

# Confirm the pod is genuinely stuck (not just slow to terminate)
kubectl get pod <pod-name> -n <namespace> -w   # Watch for 60s before proceeding

# Force delete only if pod remains Terminating with no progress
kubectl delete pod <pod-name> -n <namespace> --force --grace-period=0

# Verify the pod is gone and not rescheduled with an error state
kubectl get pod <pod-name> -n <namespace>

Drain Node (Maintenance)

# Review what will be evicted before draining
kubectl get pods --all-namespaces --field-selector spec.nodeName=<node-name>

# Cordon first to prevent new scheduling
kubectl cordon <node-name>

# Drain (evicts pods gracefully)
kubectl drain <node-name> --ignore-daemonsets --delete-emptydir-data

# Verify node is drained and no workloads remain
kubectl get pods --all-namespaces --field-selector spec.nodeName=<node-name>

# After maintenance, uncordon to restore scheduling
kubectl uncordon <node-name>
kubectl get node <node-name>   # Confirm status returns to Ready

Advanced Debugging Techniques

Debug Containers (Kubernetes 1.23+)

# Attach ephemeral debug container
kubectl debug <pod-name> -n <namespace> -it --image=nicolaka/netshoot

# Create debug copy of pod
kubectl debug <pod-name> -n <namespace> -it --copy-to=<debug-pod-name> --container=<container>

Port Forwarding for Testing

# Forward pod port to local machine
kubectl port-forward pod/<pod-name> -n <namespace> <local-port>:<pod-port>

# Forward service port
kubectl port-forward svc/<service-name> -n <namespace> <local-port>:<service-port>

Proxy for API Access

# Start kubectl proxy
kubectl proxy --port=8080

# Access API
curl http://localhost:8080/api/v1/namespaces/<namespace>/pods/<pod-name>

Custom Column Output

# Custom pod info
kubectl get pods -o custom-columns=NAME:.metadata.name,STATUS:.status.phase,IP:.status.podIP

# Node taints
kubectl get nodes -o custom-columns=NAME:.metadata.name,TAINTS:.spec.taints

Reference Documentation

Detailed Troubleshooting Guides

Consult references/troubleshooting_workflow.md for:

• Step-by-step workflows for each issue type
• Decision trees for diagnosis
• Command sequences for systematic debugging
• Quick reference command cheat sheet

Common Issues Database

Consult references/common_issues.md for:

• Detailed explanations of each common issue
• Symptoms and causes
• Specific debugging steps
• Solutions and fixes
• Prevention strategies