CoreDNS and AWS VPC CNI in EKS: Understanding Internal and Upstream Flow When people start learning EKS networking, two components create the most confusion: CoreDNS AWS VPC CNI At first, they can look similar because both are involved when one service talks to another. But their jobs are very different. A simple way to understand them is this: CoreDNS tells your Pod where to send the request VPC CNI makes sure the request can actually travel there And once you understand upstream flow , everything starts making more sense. 1. CoreDNS: The Name Resolver Inside the Cluster CoreDNS is the DNS server running inside Kubernetes. Its primary job is to resolve internal service names like this: review-service.default.svc.cluster.local When a Pod calls another Kubernetes Service using its name, CoreDNS translates that name into an IP address. Internal service lookup flow Pod ↓ CoreDNS ↓ Service IP Diagram: Internal DNS resolution order...

EKS Add-ons Explained Through Real Traffic Flow In AWS EKS, Kubernetes doesn’t run in isolation. It depends on a set of add-ons to handle: networking DNS routing storage external traffic Instead of memorizing each component separately, the easiest way to understand them is: 👉 Follow a request as it flows through the system Flow 1: External Request → Your Application Let’s say a user opens your app in the browser. Step 1: Internet → Load Balancer https://your-app.com This hits an AWS Application Load Balancer (ALB) . Created by: AWS Load Balancer Controller Step 2: ALB → Kubernetes Ingress Ingress → Service The ALB routes the request based on rules defined in your Ingress. Step 3: Service → Pod (kube-proxy) Kubernetes needs to pick a Pod. This is handled by kube-proxy receives the request selects a Pod routes traffic using iptables/IPVS Step 4: Pod Receives Traffic (VPC CNI) The Pod already has a real VPC IP ad...

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 ...