VXLAN with Flannel in Kubernetes

VXLAN with Flannel in Kubernetes is like mailing a letter inside a bigger envelope so it can travel across a physical network while pretending all the containers are sitting in the same room.

1. The Core Problem

In Kubernetes, you have multiple physical servers (called Nodes). Inside those servers, you have dozens of isolated application containers (called Pods).

Every single Pod needs its own unique IP address and needs to be able to talk directly to any other Pod on any other server. However, the physical network switches and routers connecting your servers don’t know anything about your Pods; they only know how to send traffic to the servers themselves.

2. Enter Flannel (The Delivery Coordinator)

Flannel is a tool that coordinates the networking for Kubernetes.

• It assigns a specific “neighborhood” (a subnet or range of IP addresses) to each server.

• It runs a background helper program (flanneld) on every server to keep track of which neighborhood belongs to which server.

3. Enter VXLAN (The Magic Envelope)

To actually move data between servers without confusing the physical network switches, Flannel uses a technology called VXLAN (Virtual Extensible LAN).