Pod Disruption Budgets in Kubernetes - Commands & Configuration

Introduction

Sometimes, when you update or maintain your app, some parts stop working temporarily. Pod Disruption Budgets help keep enough parts running so your app stays available during these times.

When you want to update your app without making it unavailable to users.

When you need to do maintenance on your servers but want to keep your app running smoothly.

When you run multiple copies of your app and want to make sure not too many stop at once.

When you want to control how many app parts can be stopped during automatic system updates.

When you want to avoid downtime caused by unexpected restarts or crashes.

Config File - pdb.yaml

pdb.yaml

apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: my-app-pdb
  namespace: default
spec:
  minAvailable: 2
  selector:
    matchLabels:
      app: my-app

This file tells Kubernetes to keep at least 2 pods with the label app: my-app running at all times. The minAvailable key sets the minimum number of pods that must stay up during disruptions. The selector finds the pods this rule applies to.

Commands

This command creates the Pod Disruption Budget in your Kubernetes cluster to protect your app pods during disruptions.

Terminal

kubectl apply -f pdb.yaml

Expected Output

poddisruptionbudget.policy/my-app-pdb created

This command checks the status of the Pod Disruption Budget to see how many pods are allowed to be disrupted.

Terminal

kubectl get poddisruptionbudget my-app-pdb

Expected Output

NAME          MIN AVAILABLE   MAX UNAVAILABLE   ALLOWED DISRUPTIONS   AGE

my-app-pdb   2               N/A               0                     10s

This command shows detailed information about the Pod Disruption Budget, including which pods it covers and current disruption status.

Terminal

kubectl describe poddisruptionbudget my-app-pdb

Expected Output

Name:           my-app-pdb

Namespace:      default

Min available:  2

Selector:       app=my-app

Status:

  Current Healthy: 3

  Desired Healthy: 2

  Disruptions Allowed: 1

  Expected Pods: 3

Events:          <none>

Key Concept

If you remember nothing else from this pattern, remember: Pod Disruption Budgets keep enough app parts running during updates or maintenance to avoid downtime.

Common Mistakes

Setting minAvailable higher than the total number of pods running.

This makes it impossible for Kubernetes to allow any disruptions, blocking updates or maintenance.

Set minAvailable to a number less than or equal to the total pods to allow safe disruptions.

Not matching the correct pod labels in the selector.

The Pod Disruption Budget won't protect the intended pods, risking downtime.

Use the exact labels that your app pods have in the selector section.

Summary

Create a Pod Disruption Budget YAML file to specify minimum pods that must stay running.

Apply the Pod Disruption Budget with kubectl to protect your app during disruptions.

Check the Pod Disruption Budget status and details to monitor allowed disruptions.

Practice

1. What is the main purpose of a Pod Disruption Budget in Kubernetes?

easy

A. To ensure a minimum number of pods stay available during planned disruptions

B. To automatically restart pods when they crash

C. To scale pods up or down based on CPU usage

D. To backup pod data before deletion

Solution

1. Step 1: Understand Pod Disruption Budget purpose

   A Pod Disruption Budget (PDB) is designed to keep your app available during planned changes by limiting voluntary disruptions.

2. Step 2: Match purpose to options

   To ensure a minimum number of pods stay available during planned disruptions correctly states that PDB ensures a minimum number of pods remain running during disruptions, unlike other options which describe unrelated features.

3. Final Answer:

   To ensure a minimum number of pods stay available during planned disruptions -> Option A

4. Quick Check:

   Pod Disruption Budget = availability during disruptions [OK]

Hint: PDB = minimum pods running during planned changes [OK]

Common Mistakes:

• Confusing PDB with auto-scaling
• Thinking PDB restarts crashed pods
• Assuming PDB backs up pod data

2. Which of the following is the correct way to specify a Pod Disruption Budget that allows at most 1 pod disruption at a time for pods with label app=web?

easy

A. apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
name: pdb-web
spec:
maxUnavailable: 1
selector:
matchLabels:
app: web
minReadySeconds: 10

B. apiVersion: v1
kind: PodDisruptionBudget
metadata:
name: pdb-web
spec:
minAvailable: 1
selector:
matchLabels:
app: web

C. apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
name: pdb-web
spec:
maxUnavailable: 1
selector:
matchLabels:
app: web
strategy: RollingUpdate

D. apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
name: pdb-web
spec:
maxUnavailable: 1
selector:
matchLabels:
app: web

Solution

1. Step 1: Check API version and kind

   The correct API version for PDB is policy/v1 and kind is PodDisruptionBudget.

2. Step 2: Validate spec fields for maxUnavailable and selector

   apiVersion: policy/v1 kind: PodDisruptionBudget metadata: name: pdb-web spec: maxUnavailable: 1 selector: matchLabels: app: web correctly uses maxUnavailable: 1 and a selector matching label app: web. Other options either use wrong API version, extra unsupported fields, or wrong spec keys.

3. Final Answer:

   apiVersion: policy/v1 kind: PodDisruptionBudget metadata: name: pdb-web spec: maxUnavailable: 1 selector: matchLabels: app: web -> Option D

4. Quick Check:

   Correct API and maxUnavailable syntax = apiVersion: policy/v1 kind: PodDisruptionBudget metadata: name: pdb-web spec: maxUnavailable: 1 selector: matchLabels: app: web [OK]

Hint: Use policy/v1 and maxUnavailable with correct selector [OK]

Common Mistakes:

• Using wrong API version like v1
• Adding unsupported fields like strategy
• Confusing minAvailable with maxUnavailable

3. Given this Pod Disruption Budget YAML snippet:

spec:
  minAvailable: 3
  selector:
    matchLabels:
      app: backend

If there are 5 pods with label app=backend, how many pods can be disrupted at once without violating the PDB?

medium

A. 3 pods

B. 2 pods

C. 5 pods

D. 0 pods

Solution

1. Step 1: Understand minAvailable meaning

   minAvailable: 3 means at least 3 pods must stay running during disruptions.

2. Step 2: Calculate allowed disruptions

   With 5 pods total, maximum disruptions allowed = 5 - 3 = 2 pods.

3. Final Answer:

   2 pods -> Option B

4. Quick Check:

   5 total - 3 minAvailable = 2 allowed disruptions [OK]

Hint: Allowed disruptions = total pods - minAvailable [OK]

Common Mistakes:

• Confusing minAvailable with maxUnavailable
• Assuming all pods can be disrupted
• Ignoring total pod count

4. You applied this Pod Disruption Budget:

apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: pdb-db
spec:
  maxUnavailable: 2
  selector:
    matchLabels:
      app: database

But Kubernetes reports an error: "spec.maxUnavailable: Invalid value: "2": must be less than the number of pods selected by the label selector". What is the likely cause?

medium

A. There are fewer than 3 pods with label app=database

B. maxUnavailable must be a percentage, not a number

C. The selector label is incorrect syntax

D. PodDisruptionBudget requires minAvailable, not maxUnavailable

Solution

1. Step 1: Understand maxUnavailable validation

   maxUnavailable must be less than the total number of pods matched by the selector.

2. Step 2: Analyze error message meaning

   The error says "must be less than the number of pods" meaning the number of pods with label app=database is less than or equal to 2.

3. Final Answer:

   There are fewer than 3 pods with label app=database -> Option A

4. Quick Check:

   maxUnavailable < total pods = error if not [OK]

Hint: maxUnavailable must be less than pod count [OK]

Common Mistakes:

• Using maxUnavailable as percentage incorrectly
• Miswriting selector labels
• Thinking minAvailable is mandatory

5. You have a deployment with 10 pods labeled app=frontend. You want to ensure that during voluntary disruptions, at least 80% of pods remain available. Which Pod Disruption Budget spec is correct?

hard

A. spec:
minAvailable: 80
selector:
matchLabels:
app: frontend

B. spec:
maxUnavailable: 8
selector:
matchLabels:
app: frontend

C. spec:
maxUnavailable: 20%
selector:
matchLabels:
app: frontend

D. spec:
minAvailable: 20%
selector:
matchLabels:
app: frontend

Solution

1. Step 1: Understand percentage usage in PDB

   maxUnavailable and minAvailable can accept percentages. To keep 80% available, maxUnavailable should be 20%.

2. Step 2: Evaluate options for correctness

   spec: minAvailable: 80 selector: matchLabels: app: frontend: minAvailable: 80 - absolute value exceeds total pods (10) - invalid.
   spec: maxUnavailable: 8 selector: matchLabels: app: frontend: maxUnavailable: 8 - allows 8 pods unavailable (only 20% available) - insufficient.
   spec: maxUnavailable: 20% selector: matchLabels: app: frontend: maxUnavailable: 20% - allows 20% (~2 pods) unavailable - ensures 80% available - correct.
   spec: minAvailable: 20% selector: matchLabels: app: frontend: minAvailable: 20% - ensures only at least 20% available - insufficient.

3. Final Answer:

   spec: maxUnavailable: 20% selector: matchLabels: app: frontend -> Option C

4. Quick Check:

   20% maxUnavailable = 80% pods available [OK]

Hint: Use maxUnavailable: 20% to keep 80% pods up [OK]

Common Mistakes:

• Using minAvailable with percentage incorrectly
• Confusing absolute numbers with percentages
• Not matching selector labels properly