k8s-debug

これはレビュー時に保存された抜粋です。完全で最新の内容は外部ソースを確認してください。

---
name: k8s-debug
description: Diagnose and fix Kubernetes pods, CrashLoopBackOff, Pending, DNS, networking, storage, and rollout failures with kubectl.
---

# Kubernetes Debugging Skill

## Overview

Systematic toolkit for debugging Kubernetes clusters, workloads, networking, and storage with a deterministic, safety-first workflow.

## Trigger Phrases

Use this skill when requests resemble:
- "My pod is in `CrashLoopBackOff`; help me find the root cause."
- "Service DNS works in one pod but not another."
- "Deployment rollout is stuck."
- "Pods are `Pending` and not scheduling."
- "Cluster health looks degraded after a change."
- "PVC is pending and pods cannot mount storage."

## Prerequisites

Run from the skill directory (`devops-skills-plugin/skills/k8s-debug`) so relative script paths work as written.

### Required
- `kubectl` installed and configured.
- An active cluster context.
- Read access to namespaces, pods, events, services, and nodes.

Quick preflight:

```bash
kubectl config current-context
kubectl auth can-i get pods -A
kubectl auth can-i get events -A
kubectl get ns
```

### Optional but Recommended
- `jq` for more precise filtering in `./scripts/cluster_health.sh`.
- Metrics API (`metrics-server`) for `kubectl top`.
- In-container debug tools (`nslookup`, `getent`, `curl`, `wget`, `ip`) for deep network tests.

Fallback behavior:
- If optional tools are missing, scripts continue and print warnings with reduced output.
- If `kubectl top` is unavailable, continue with `kubectl describe` and events.

## When to Use This Skill

Use this skill for:
- Pod failures (CrashLoopBackOff, ImagePullBackOff, Pending, OOMKilled)
- Service connectivity or DNS resolution issues
- Network policy or ingress problems
- Volume and storage mount failures
- Deployment rollout issues
- Cluster health or performance degradation
- Resource exhaustion (CPU/memory)
- Configuration problems (ConfigMaps, Secrets, RBAC)

## Safety Rules for Disruptive Commands

Default mode is read-only diagnosis first. Only execute disruptive commands after confirming blast radius and rollback.

Commands requiring explicit confirmation:
- `kubectl delete pod ... --force --grace-period=0`
- `kubectl drain ...`
- `kubectl rollout restart ...`
- `kubectl rollout undo ...`
- `kubectl debug ... --copy-to=...`

Before disruptive actions:
```bash
# Snapshot current state for rollback and incident notes
kubectl get deploy,rs,pod,svc -n <namespace> -o wide
kubectl get pod <pod-name> -n <namespace> -o yaml > before-<pod-name>.yaml
kubectl get events -n <namespace> --sort-by='.lastTimestamp' > before-events.txt
```

## Reference Navigation Map

Load only the section needed for the observed symptom.

| Symptom / Need | Open | Start section |
| --- | --- | --- |
| You need an end-to-end diagnosis path | `./references/troubleshooting_workflow.md` | `General Debugging Workflow` |
| Pod state is `Pending`, `CrashLoopBackOff`, or `ImagePullBackOff` | `./references/troubleshooting_workflow.md` | `Pod Lifecycle Troubleshooting` |
| Service reachability or DNS failure | `./references/troubleshooting_workflow.md` | `Network Troubleshooting Workflow` |
| Node pressure or performance regression | `./references/troubleshooting_workflow.md` | `Resource and Performance Workflow` |
| PVC / PV / storage class issues | `./references/troubleshooting_workflow.md` | `Storage Troubleshooting Workflow` |
| Quick symptom-to-fix lookup | `./references/common_issues.md` | matching issue heading |
| Post-mortem fix options for known issues | `./references/common_issues.md` | `Solutions` sections |

## Scripts Overview

| Script | Purpose | Required args | Optional args | Output | Fallback behavior |
| --- | --- | --- | --- | --- | --- |
| `./scripts/cluster_health.sh` | Cluster-wide health snapshot (nodes, workloads, events, common failure states) | None | `--strict`, `K8S_REQUEST_TIMEOUT` env var | Sectioned report to stdout | Continues on check failures, tracks them in summary and exit c