Kubernetes Network Fundamentals: A Pod Is a Phone

Four Concepts Before Everything Else

Before the rest of this series makes sense, you need four networking ideas. Think of a Kubernetes cluster as an office building.

IP Address = Extension Number

Each pod is a desk with its own extension number.

The 10.0.x.x range is private. Only pods inside the cluster can use it.

Port = Room Number

One pod can run many services. The port number picks which one you want.

Pod 10.0.2.3
  room :9222  →  Chrome DevTools
  room :8080  →  Web server
  room :9090  →  Metrics

A full address is extension:room = 10.0.2.3:9222.

localhost (127.0.0.1) = Group Chat

Every pod has a private group chat. Only apps inside the same pod can see the messages.

0.0.0.0 = Accept All Calls

0.0.0.0 is not an address anyone dials. It is a setting the app uses at startup: accept outside calls or not.

Same Pod = Group Chat Works

All containers in one pod share a network namespace. Like apps on the same phone, they all use the same group chat.

Different Pods = Must Dial the Extension

“127.0.0.1 = this pod only. 10.0.x.x = the number other pods dial. 0.0.0.0 = accept both.”

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References:

• Cloudflare: What is an IP Address?
• Difference Between 127.0.0.1 and 0.0.0.0
• Why Pod Containers Talk on Localhost
• Pod-to-Pod Communication

Related: learn how Chrome uses these network rules in the Chrome DevTools Protocol deep dive, or go back to the series overview.