managing-k8s-pod-disruption

name	managing-k8s-pod-disruption
description	Use when working with K8S Pod Disruption — kubernetes PodDisruptionBudget management and disruption analysis. Covers PDB inventory, allowed disruptions, eviction status, node drain impact, workload protection coverage, and PDB misconfiguration detection. Use when auditing disruption protection, planning node maintenance, debugging stuck evictions, or reviewing PDB coverage across workloads.
connection_type	k8s
preload	false

Kubernetes PodDisruptionBudget Skill

Manage and analyze PodDisruptionBudgets for workload availability during disruptions.

MANDATORY: Discovery-First Pattern

Always list PDBs and their status before analyzing disruption impact.

Phase 1: Discovery

#!/bin/bash

echo "=== PodDisruptionBudgets (all namespaces) ==="
kubectl get pdb --all-namespaces -o custom-columns='NAMESPACE:.metadata.namespace,NAME:.metadata.name,MIN-AVAILABLE:.spec.minAvailable,MAX-UNAVAILABLE:.spec.maxUnavailable,ALLOWED-DISRUPTIONS:.status.disruptionsAllowed,CURRENT:.status.currentHealthy,DESIRED:.status.desiredHealthy,EXPECTED:.status.expectedPods' 2>/dev/null

echo ""
echo "=== PDB Selector Mapping ==="
kubectl get pdb --all-namespaces -o json 2>/dev/null | jq -r '
  .items[] |
  "\(.metadata.namespace)/\(.metadata.name)\tSelector:\(.spec.selector.matchLabels | to_entries | map("\(.key)=\(.value)") | join(","))"
' | head -20

Phase 2: Analysis

#!/bin/bash

echo "=== Blocking PDBs (zero disruptions allowed) ==="
kubectl get pdb --all-namespaces -o json 2>/dev/null | jq -r '
  .items[] |
  select(.status.disruptionsAllowed == 0) |
  "\(.metadata.namespace)/\(.metadata.name)\tAllowed:0\tCurrent:\(.status.currentHealthy)/\(.status.desiredHealthy)\tMinAvailable:\(.spec.minAvailable // "N/A")\tMaxUnavailable:\(.spec.maxUnavailable // "N/A")"
' | head -15

echo ""
echo "=== Misconfigured PDBs ==="
kubectl get pdb --all-namespaces -o json 2>/dev/null | jq -r '
  .items[] |
  select(
    (.spec.minAvailable == "100%" or .spec.maxUnavailable == 0 or .spec.maxUnavailable == "0%") or
    (.status.expectedPods == 0)
  ) |
  "\(.metadata.namespace)/\(.metadata.name)\tReason:" +
  (if .spec.minAvailable == "100%" then "minAvailable=100% blocks all evictions"
   elif .spec.maxUnavailable == 0 or .spec.maxUnavailable == "0%" then "maxUnavailable=0 blocks all evictions"
   elif .status.expectedPods == 0 then "no matching pods found"
   else "unknown" end)
' | head -10

echo ""
echo "=== Workloads Without PDBs ==="
kubectl get deployments --all-namespaces -o json 2>/dev/null | jq -r '
  .items[] |
  select(.spec.replicas > 1) |
  "\(.metadata.namespace)/\(.metadata.name)\tReplicas:\(.spec.replicas)"
' > /tmp/deployments.txt
kubectl get pdb --all-namespaces -o json 2>/dev/null | jq -r '
  .items[] |
  "\(.metadata.namespace)/\(.spec.selector.matchLabels | to_entries | map(.value) | join("-"))"
' > /tmp/pdbs.txt
echo "Multi-replica deployments without PDB protection:"
wc -l /tmp/deployments.txt /tmp/pdbs.txt 2>/dev/null
head -10 /tmp/deployments.txt

echo ""
echo "=== Node Drain Simulation ==="
echo "Nodes and their pod counts:"
kubectl get pods --all-namespaces -o json 2>/dev/null | jq -r '
  [.items[] | select(.status.phase == "Running") | .spec.nodeName] |
  group_by(.) | map({node: .[0], pods: length}) |
  sort_by(-.pods)[] |
  "\(.node)\t\(.pods) pods"
' |  -10

 
 
kubectl get events --all-namespaces --field-selector reason=Evicted -o custom-columns= 2>/dev/null |  -10

Output Format

• Target ≤50 lines per output
• Use -o custom-columns for PDB listings
• Show disruptionsAllowed prominently -- zero means blocking
• Flag misconfigured PDBs (100% minAvailable, 0 maxUnavailable)
• Never modify PDBs in analysis -- read-only inspection

Anti-Hallucination Rules

1. NEVER assume resource names — always discover via CLI/API in Phase 1 before referencing in Phase 2.
2. NEVER fabricate metric names or dimensions — verify against the service documentation or --help output.
3. NEVER mix CLI commands between service versions — confirm which version/API you are targeting.
4. ALWAYS use the discovery → verify → analyze chain — every resource referenced must have been discovered first.
5. ALWAYS handle empty results gracefully — an empty response is valid data, not an error to retry.

Counter-Rationalizations

Shortcut	Counter	Why
"I'll skip discovery and check known resources"	Always run Phase 1 discovery first	Resource names change, new resources appear — assumed names cause errors
"The user only asked for a quick check"	Follow the full discovery → analysis flow	Quick checks miss critical issues; structured analysis catches silent failures
"Default configuration is probably fine"	Audit configuration explicitly	Defaults often leave logging, security, and optimization features disabled
"Metrics aren't needed for this"	Always check relevant metrics when available	API/CLI responses show current state; metrics reveal trends and intermittent issues
"I don't have access to that"	Try the command and report the actual error	Assumed permission failures prevent useful investigation; actual errors are informative

Common Pitfalls

• Blocking drain: PDBs with minAvailable=100% or maxUnavailable=0 block node drains indefinitely
• No matching pods: PDB selector not matching any pods makes the PDB ineffective -- check labels
• Single replica: PDB on a single-replica deployment with minAvailable=1 blocks all evictions
• Percentage vs absolute: minAvailable can be number or percentage -- percentage rounds up
• Unhealthy pods: Unhealthy pods count against currentHealthy -- can prevent disruptions even when enough replicas exist
• StatefulSets: PDBs are critical for StatefulSets during rolling updates -- ensure maxUnavailable allows progress
• Cluster autoscaler: CA respects PDBs -- blocking PDBs prevent node scale-down
• Multiple PDBs: Multiple PDBs selecting the same pods all must allow disruption -- most restrictive wins