🚀 Intro: Why Pods Need Preference?

Imagine you’re allocating rooms to guests in a hotel:

Some want sea view 🌊
Some are okay with any room, but prefer corner ones 🛏️

Similarly, in Kubernetes — Pods sometimes need to run on specific nodes.

That’s where Node Affinity comes in.

🎯 What is Node Affinity?

Node Affinity tells the Kubernetes scheduler:

"Hey, please place my Pod only on a node that matches certain labels."

It gives us control over Pod placement.

You define the labels that a Pod's node must (or should) have.

🧱 Types of Node Affinity:

Type	What it means
`requiredDuringSchedulingIgnoredDuringExecution`	Hard Rule → Must follow
`preferredDuringSchedulingIgnoredDuringExecution`	Soft Rule → Best effort

🛠️ Example 1: Hard Rule

I want this pod to run only on SSD-based nodes:

If no node has disktype=ssd, the pod won’t run 🚫

✨ Example 2: Soft Rule

I prefer my pod to run in zone us-east-1a:

If zone us-east-1a is available, great! If not, no problem — pod will still run.

🔍 Node Affinity vs Node Selector

Feature	Node Selector	Node Affinity
Syntax	Basic	Flexible
Expressions	❌ No	✅ Yes
Soft Preference	❌ No	✅ Yes

📌 CKA Exam Tip

Expect YAML-based MCQs like:

Which node will this pod schedule on?
What happens if no node matches?
Difference between required vs preferred?

💭 My Thoughts

Node Affinity feels like setting boundaries for your pods —
"Run where you’re most productive" 😄
CKA syllabus has so much depth, but these concepts really help you think like a schedule

K8s Node Affinity Explained