☸️ What Are EKS Add-ons? (Simple Explanation)

What Are EKS Add-ons? (Simple Explanation)

When we create an EKS (Elastic Kubernetes Service) cluster, AWS automatically installs or expects some add-ons.

These add-ons are important because Kubernetes alone does not know how to:

  • connect to AWS network
  • resolve DNS
  • route traffic

So AWS gives us these components to make the cluster work properly.

Core EKS Add-ons

1. VPC CNI (Networking)

Full name: Amazon VPC CNI

What it does:
It assigns an IP address to each Pod from the VPC subnet.

Why it is important:
Pods behave like real AWS resources inside your VPC.

Example:
A Pod may get an IP like 10.0.1.25.

2. CoreDNS (DNS inside cluster)

What it does:
It converts a service name into an IP address. 

my-service.default.svc.cluster.local

It also forwards external DNS requests to the VPC DNS resolver.

3. kube-proxy (Service routing)

What it does:
It routes traffic from a Service to the correct Pod.

How it works:
Uses iptables or IPVS.

Example:
You hit a Service IP → traffic goes to correct Pod.

4. EBS CSI Driver (Storage)

What it does:
Allows Pods to use AWS EBS volumes.

  • Databases
  • Stateful apps

5. EFS CSI Driver (Shared storage)

What it does:
Allows multiple Pods to share the same storage.

Backed by: AWS EFS

6. AWS Load Balancer Controller

What it does:
Converts Kubernetes Ingress into AWS ALB/NLB.

Used for:
Exposing applications publicly or internally.

Easy Way to Remember

Add-on Purpose
VPC CNI Networking (Pod IP)
CoreDNS DNS
kube-proxy Routing
CSI Drivers Storage
AWS Load Balancer Controller External traffic

Important Note

By default, Pods can communicate freely inside the cluster.

To restrict traffic, you must use Network Policies.

Final Thought

EKS manages Kubernetes for you, but these add-ons are what actually make it work inside AWS.

Without them, your cluster will not function properly.

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