Kubernetes CNI Plugins Compared

💡 Quick Answer: Compare Calico, Cilium, Flannel, and Multus CNI plugins for Kubernetes. Performance benchmarks, features, and selection criteria for your cluster.

The Problem

This is a critical skill for managing production Kubernetes clusters at scale. Without it, teams face operational complexity, security risks, and reliability issues.

The Solution

Choose a CNI by requirement: Cilium (eBPF) for performance, L7 policy, and observability; Calico for mature policy and BGP; Flannel for a simple overlay; Multus to attach multiple interfaces (common for GPU/RDMA workloads).

Plugin	Data plane	Network policy	Best for
Cilium	eBPF	L3–L7	Performance, observability, policy
Calico	iptables/eBPF	L3–L4	BGP, large clusters
Flannel	VXLAN	none	Simple overlays
Multus	meta-plugin	delegates	Multiple NICs, SR-IOV

Install Cilium with Helm and validate the data plane:

helm install cilium cilium/cilium --namespace kube-system \
  --set kubeProxyReplacement=true

cilium status --wait
cilium connectivity test

Whichever CNI you pick, start with a default-deny policy and open traffic explicitly:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-ingress
spec:
  podSelector: {}
  policyTypes: ["Ingress"]

Common Issues

Troubleshooting

Check logs and events first. Most issues have clear error messages pointing to the root cause.

Best Practices

Follow the principle of least privilege for all configurations
Test in staging before applying to production
Monitor and alert on key metrics
Document your runbooks for the team

Key Takeaways

Essential knowledge for Kubernetes operations at scale
Start simple and evolve your approach as needed
Automation reduces human error and operational toil
Share learnings across your team