Pod Disruption Budgets in Kubernetes - Step-by-Step Execution

Process Flow - Pod Disruption Budgets

Define PDB YAML

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Apply PDB to Cluster

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Kubernetes Controller Watches PDB

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Pod Eviction Request

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Check PDB Conditions

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Allow Eviction

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Pod Removed

Shows how a Pod Disruption Budget (PDB) is defined, applied, and used by Kubernetes to allow or block pod evictions during disruptions.

Execution Sample

Kubernetes

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

Defines a PDB that requires at least 2 pods with label app=myapp to be available during disruptions.

Process Table

Step	Event	Pods Available	minAvailable	Eviction Allowed?	Reason
1	Initial state	3	2	Yes	Pods meet minAvailable requirement
2	Eviction request for 1 pod	3	2	Yes	Eviction keeps pods >= minAvailable
3	After eviction, pods available	2	2	N/A	Pods still meet minAvailable
4	Eviction request for another pod	2	2	No	Eviction would reduce pods below minAvailable
5	Eviction blocked	2	2	N/A	PDB prevents disruption

💡 Eviction blocked when pods available would drop below minAvailable

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
Pods Available	3	3	2	2	2
Eviction Allowed	Yes	Yes	N/A	No	No

Key Moments - 2 Insights

Why is eviction allowed at step 2 but blocked at step 4?

At step 2, evicting one pod keeps the available pods at 2, which meets the minAvailable requirement (see execution_table rows 2 and 3). At step 4, evicting another pod would reduce pods below minAvailable, so eviction is blocked (execution_table row 4).

What does minAvailable mean in a Pod Disruption Budget?

minAvailable is the minimum number of pods that must be running during voluntary disruptions. Kubernetes uses this to decide if it can allow pod evictions without hurting availability (refer to execution_table column 'minAvailable').

Visual Quiz - 3 Questions

Look at the execution table, how many pods are available after the first eviction?

A 1

B 2

C 3

D 0

💡 Hint

Check the 'Pods Available' column at Step 3 in the execution_table.

At which step does Kubernetes block pod eviction due to PDB?

A Step 2

B Step 3

C Step 4

D Step 1

💡 Hint

Look at the 'Eviction Allowed?' column in execution_table to find where eviction is 'No'.

If minAvailable was set to 1 instead of 2, what would happen at step 4?

A Eviction would be allowed

B Eviction would still be blocked

C Pods available would increase

D PDB would be ignored

💡 Hint

Compare minAvailable value and pods available at step 4 in variable_tracker and execution_table.

Concept Snapshot

Pod Disruption Budget (PDB) controls voluntary pod evictions.
Define PDB with minAvailable or maxUnavailable.
Kubernetes checks PDB before evicting pods.
Eviction allowed only if availability stays above minAvailable.
Prevents too many pods going down at once.
Use PDB to keep app stable during maintenance.

Full Transcript

Pod Disruption Budgets help keep your app running smoothly by limiting how many pods can be taken down at once. You write a PDB YAML file specifying minAvailable pods. Kubernetes watches this and blocks pod evictions if removing a pod would drop availability below that number. For example, if you have 3 pods and minAvailable is 2, Kubernetes allows evicting one pod but blocks evicting a second pod until one comes back. This way, your app stays healthy during updates or node maintenance.