Kubernetes CNI Comparison

Kubernetes relies on CNI plugins (Container Network Interface) to handle Pod networking. They assign IPs, enable Pod-to-Pod communication, enforce network policies, and route traffic across nodes.

This guide compares the four most widely used CNIs:

  • Calico
  • Cilium
  • Flannel
  • Weave Net

1. CNI Comparison Table

CNI Networking Model Network Policies Performance Best Use Case
Calico BGP routing / VXLAN Yes (very strong) ⭐⭐⭐⭐ Production, security-focused clusters
Cilium eBPF (high performance) Yes (L3/L4/L7) ⭐⭐⭐⭐⭐ High performance, zero-overhead networking
Flannel VXLAN / host-gw No ⭐⭐⭐ Simple labs and lightweight clusters
Weave Net Encrypted mesh overlay Yes ⭐⭐⭐ Small/medium clusters needing encryption

2. Advantages & Disadvantages

Calico
  • Advantages:
    • Best-in-class Network Policy support
    • High performance with BGP
    • Can operate without overlays (native routing)
  • Disadvantages:
    • More complex to configure
    • BGP troubleshooting may require expertise
Cilium
  • Advantages:
    • Uses eBPF → fastest CNI available
    • L7 policies & observability
    • Deep integration with service mesh modes
  • Disadvantages:
    • Requires modern Linux kernels
    • More advanced learning curve
Flannel
  • Advantages:
    • Simplest to deploy
    • Lightweight and stable
    • Perfect for test or dev clusters
  • Disadvantages:
    • No Network Policies
    • Lower performance compared to Cilium/Calico
Weave Net
  • Advantages:
    • Automatic encryption between nodes
    • Zero-config discovery
    • Network policies supported
  • Disadvantages:
    • Weave Net encryption can reduce throughput
    • Higher resource usage on nodes

3. Which CNI Should You Use?

  • Use Calico if: you need strong network policies and scalable routing.
  • Use Cilium if: you want maximum performance, observability, or service mesh-like features.
  • Use Flannel if: you're building a simple lab or lightweight cluster.
  • Use Weave Net if: you want built-in encryption without extra components.

4. Installation Examples

Install Calico
kubectl apply -f https://docs.projectcalico.org/manifests/calico.yaml
Install Cilium
curl -L --remote-name https://github.com/cilium/cilium-cli/releases/latest/download/cilium-linux-amd64.tar.gz
tar xzvf cilium-linux-amd64.tar.gz
sudo mv cilium /usr/local/bin/
cilium install
Install Flannel
kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
Install Weave Net
kubectl apply -f https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')

This comparison should help you choose the right CNI depending on your Kubernetes cluster's scale, security requirements, and performance goals.