TechOps Examples
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IN TODAY'S EDITION
🧠 Use Case
How Kubernetes Pod Disruption Budgets Work and How to Use PDBs
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🧠 USE CASE
How Kubernetes Pod Disruption Budgets Work and How to Use PDBs
Have you ever faced a situation where your application suddenly went down during a cluster upgrade or scaling event? Frustrating, right?
Losing pods at the wrong moment can mean downtime, unhappy users, and stress all around. Well, here’s where Pod Disruption Budgets (PDB) step in to save the day.
What Exactly is a Pod Disruption Budget (PDB)?
A PDB makes sure that during voluntary disruptions (like a node drain) or involuntary events (like a node crash), a certain number of pods remain running. Without it, Kubernetes could easily kill off too many pods at once, leaving your service unavailable.
What Happens Without a PDB?
Imagine this: you’ve got 3 nodes, and your app is running 2 pods—App 1 on Node 1 and App 2 on Node 2. When Node 1 gets drained, App 1 is terminated, but App 3 is still pending and hasn’t started on Node 3 yet.
Now, if Node 2 gets drained while App 3 is still pending, App 2 is terminated as well. What are you left with? No healthy pods. Your service is down until the new pod is up.
What Happens With a PDB?
If you configure a PDB requiring that at least 1 pod must be running, this changes everything. When Node 1 is drained and App 1 terminates, App 3 starts getting ready. But if the system tries to drain Node 2 before App 3 is running, Kubernetes will block the drain to keep App 2 alive. This way, you’ll never be left without healthy pods, ensuring continuous service.
How to Implement a Pod Disruption Budget ?
Let’s set up a techopsexamples deployment with 6 replicas and a PDB to ensure that at least 3 pods remain available during any disruption.
Step 1: Create the Deployment
apiVersion: apps/v1
kind: Deployment
metadata:
name: teg-app
namespace: production
spec:
replicas: 6
selector:
matchLabels:
app: teg
template:
metadata:
labels:
app: teg
spec:
containers:
- name: teg-container
image: teg-app:v1.0Apply the deployment:
kubectl apply -f teg-deployment.yamlCheck your pods:
kubectl get podsYou should see something like:
NAME READY STATUS
teg-app-6d9fc4fc8b-xyz 1/1 Running
teg-app-6d9fc4fc8b-abc 1/1 RunningStep 2: Create the PDB
Lets, create a PDB to ensure at least 3 pods are always available:
apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
name: teg-pdb
namespace: production
spec:
minAvailable: 3
selector:
matchLabels:
app: tegApply the PDB:
kubectl apply -f teg-pdb.yamlCheck the PDB:
kubectl get poddisruptionbudgetsYou should see something like:
NAME MIN AVAILABLE ALLOWED DISRUPTIONS AGE
teg-pdb 3 3 30sStep 3: Test the PDB by Draining a Node
Now simulate a disruption by draining a node:
kubectl drain <node-name> --ignore-daemonsets --delete-emptydir-dataIf too many pods would be impacted, Kubernetes will block the drain:
error: Cannot evict pod as it would violate the pod's disruption budget.This confirms that your PDB is working and keeping your app alive during disruptions.
So, Why Use PDB?
If you’ve ever lost too many pods during scaling events, maintenance, or other disruptions, a PDB could be an ideal solution. It ensures your app always has enough healthy pods to keep serving users.
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