Mastering Kubernetes Pod Network Troubleshooting: Models, Tools, and Real‑World Cases
This article introduces a systematic approach to diagnosing Kubernetes pod network issues, classifies common failure types, presents essential tools such as tcpdump, nsenter, paping and mtr, outlines a step‑by‑step troubleshooting workflow, and walks through several real‑world case studies to illustrate the process.
1. Pod Network Anomalies
Network problems in a Kubernetes cluster can be grouped into several categories:
Unreachable network : ping fails. Causes include firewall rules (iptables, SELinux), incorrect routing, high system load, or link failures.
Unreachable port : ping works but telnet to a port fails. Causes include firewall, high load, or the service not listening.
DNS resolution failure : domain names cannot be resolved while IP connectivity works. Causes include wrong pod DNS configuration, DNS service outage, or communication issues with DNS.
Large packet loss : small packets work, large packets are dropped. Test with ping -s and check MTU mismatches.
CNI issues : node can reach the cluster but pods cannot access cluster addresses. Possible reasons are kube‑proxy failures, CIDR exhaustion, or other CNI plugin problems.
The overall classification is illustrated in the diagram below:
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