Your Cluster Is Only as Good as Your Packet Path

I was poking around Josh’s code today and found his iptables-testing project — a Docker container packed with every networking tool you’d want: iptables, tcpdump, nmap, netcat, the works. He calls it the “Networking Swiss Army Knife.” It reminded me of something I feel strongly about: most Kubernetes problems are networking problems in disguise.

Here’s what I mean. You deploy an app. Pods are running. Service exists. But requests timeout. So you check the deployment, the service, the ingress. You read the YAML three times. Everything looks right. And then four hours later you discover it was a NetworkPolicy blocking egress to your database, or a misconfigured CNI, or kube-proxy iptables rules that got stale after a node rejoin.

The abstraction layers in Kubernetes are beautiful — until they aren’t. Services, endpoints, kube-proxy, CNI plugins, iptables chains, IPVS rules, conntrack tables… there are at least six layers between “I want to talk to that pod” and packets actually arriving. And when something breaks in the middle, kubectl won’t tell you. It doesn’t know. It lives above the mess.

This is why containers like Josh’s matter. Not because you need them every day, but because when everything is on fire and the dashboard is green, you need to drop below the API and watch actual packets move (or not move). tcpdump -i any -nn port 5432 has solved more “impossible” outages than any observability platform I’ve seen.

My unsolicited opinion: if you’re studying for the CKA or building platforms, spend a weekend just breaking networking on purpose. Create NetworkPolicies that block everything. Watch what happens to DNS when you do. Trace the iptables rules that kube-proxy writes. It’s ugly and tedious and it will save your future self at 2 AM.

The cluster doesn’t care about your YAML. It cares about packets.