CNI Comparison

Calico Flannel Weave Cilium Antrea

A comprehensive comparison of Kubernetes CNI plugins including Calico, Flannel, Weave, Cilium, and Antrea. Learn about features, performance, use cases, and how to choose the right CNI for your cluster.

Calico Flannel Weave Cilium Antrea

What is a CNI Plugin?

The Container Network Interface (CNI) is a standard for configuring network interfaces in Linux containers. CNI plugins are responsible for providing network connectivity to pods in a Kubernetes cluster. They handle IP address allocation, routing, and network policy enforcement.

Choosing the right CNI plugin is critical for cluster performance, security, and operational complexity. Each CNI has different trade-offs in terms of features, performance, and ease of use.

Key CNI Considerations:

Performance: Throughput, latency, and resource usage
Network Policy: Support for Kubernetes NetworkPolicy
Feature Set: Encryption, service mesh integration, eBPF
Operational Complexity: Installation, configuration, troubleshooting
Ecosystem: Community support, documentation, integrations

CNI Plugin Comparison

Calico

Flannel

Simple, widely adopted

Flannel is the simplest CNI plugin. Uses overlay networking (VXLAN or host-gw). Easy to set up but lacks network policy support.

Simple setup, low resource usage

No NetworkPolicy, limited features

Small clusters, testing, development

Weave Net

DNS and encryption built-in

Weave provides automatic service discovery, encryption, and simple networking. Includes built-in DNS and can run in SNAT or IP-in-IP modes.

Built-in DNS, encryption, simple

Performance overhead, less popular

Small to medium clusters, secure workloads

Cilium

eBPF-powered networking

Cilium uses eBPF for high-performance networking and security. Provides deep observability, service mesh, and advanced network policies. Identity-based security.

eBPF performance, advanced security, observability

Complex, requires Linux 5.4+

High performance, security, advanced networking

Antrea

Open vSwitch based

Antrea uses Open vSwitch (OVS) as the networking data plane. Provides Kubernetes NetworkPolicy and supports eBPF for performance. VMware's CNI of choice.

OVS reliability, NetworkPolicy, eBPF support

OVS overhead, smaller community

Enterprise, VMware environments

Calico: The Industry Standard

Calico is the most widely deployed CNI plugin in production Kubernetes clusters. It provides a comprehensive networking solution with advanced features including:

                # Install Calico
kubectl apply -f https://raw.githubusercontent.com/projectcalico/calico/v3.27/manifests/calico.yaml

# Verify Calico pods
kubectl get pods -n kube-system -l k8s-app=calico-node

# Calico NetworkPolicy
apiVersion: projectcalico.org/v3
kind: NetworkPolicy
metadata:
  name: allow-frontend
  namespace: default
spec:
  selector: app == 'backend'
  types:
  - Ingress
  ingress:
  - action: Allow
    protocol: TCP
    source:
      selector: app == 'frontend'
    destination:
      ports:
      - 8080

# Calico eBPF mode (high performance)
# Enable in installation manifest
apiVersion: operator.tigera.io/v1
kind: Installation
metadata:
  name: default
spec:
  calicoNetwork:
    linuxDataplane: BPF

# Calico BGP configuration
apiVersion: projectcalico.org/v3
kind: BGPPeer
metadata:
  name: external-bgp
spec:
  peerIP: 192.168.1.100
  asNumber: 65000
            

Calico Advantages:

Full NetworkPolicy enforcement (including egress)
BGP routing for direct pod-to-pod communication
eBPF dataplane for high performance
Rich feature set (wireguard encryption, service mesh)
Strong community and documentation

Cilium: The Future with eBPF

Cilium represents the next generation of CNI plugins, leveraging eBPF (extended Berkeley Packet Filter) for high-performance networking and security. It provides deep observability and identity-based security.

                # Install Cilium with Helm
helm repo add cilium https://helm.cilium.io/
helm repo update
helm install cilium cilium/cilium --namespace kube-system \
  --set ipam.mode=kubernetes \
  --set routingMode=native \
  --set hubble.enabled=true \
  --set hubble.relay.enabled=true \
  --set hubble.ui.enabled=true

# Verify Cilium status
kubectl get pods -n kube-system -l k8s-app=cilium
cilium status

# Cilium NetworkPolicy (L7-aware)
apiVersion: cilium.io/v2
kind: CiliumNetworkPolicy
metadata:
  name: allow-http
spec:
  endpointSelector:
    matchLabels:
      app: backend
  ingress:
  - fromEndpoints:
    - matchLabels:
        app: frontend
    toPorts:
    - ports:
      - port: "8080"
        protocol: TCP
      rules:
        http:
        - method: GET
          path: "/api/users"

# Enable Hubble observability
cilium hubble enable
cilium hubble ui

# View network flows
hubble observe
hubble observe --from-label app=frontend
hubble observe --to-service kube-dns
            

Cilium Key Features:

eBPF Performance: High throughput, low latency
Identity-Based Security: Labels instead of IPs
L7 Policies: HTTP, Kafka, DNS-aware policies
Hubble Observability: Flow logs, service maps
Service Mesh: Integrated service mesh capabilities

Cilium Requirements: Cilium requires Linux kernel 5.4+ for eBPF features. It's also more complex to configure than simpler CNIs like Flannel. Consider these trade-offs when choosing Cilium.

Flannel: Simple and Reliable

Flannel is the simplest CNI plugin, designed to be easy to install and operate. It uses overlay networking (VXLAN, host-gw, or UDP) to provide pod-to-pod communication.

                # Install Flannel
kubectl apply -f https://github.com/flannel-io/flannel/releases/latest/download/kube-flannel.yml

# Verify Flannel pods
kubectl get pods -n kube-system -l app=flannel

# Flannel configuration (configmap)
apiVersion: v1
kind: ConfigMap
metadata:
  name: kube-flannel-cfg
  namespace: kube-system
data:
  net-conf.json: |
    {
      "Network": "10.244.0.0/16",
      "Backend": {
        "Type": "vxlan"
      }
    }

# Alternative backend: host-gw (no overlay)
# "Backend": {
#   "Type": "host-gw"
# }

# Check Flannel subnet allocation
kubectl exec -n kube-system -it  -- cat /run/flannel/subnet.env
            

Flannel Use Cases:

Development and testing environments
Small clusters with simple networking needs
When network policy is not required
Quick cluster setup and prototyping
Resource-constrained environments

Antrea: Enterprise Grade with OVS

Antrea is a CNI plugin that uses Open vSwitch (OVS) as the networking data plane. It's the CNI of choice for VMware Tanzu and provides enterprise-grade networking features.

                # Install Antrea
kubectl apply -f https://github.com/antrea-io/antrea/releases/latest/download/antrea.yml

# Verify Antrea pods
kubectl get pods -n kube-system -l app=antrea

# Antrea NetworkPolicy (Kubernetes API)
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: antrea-policy
spec:
  podSelector:
    matchLabels:
      app: backend
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: frontend
    ports:
    - port: 8080

# Antrea-specific features (traceflow)
apiVersion: antrea.io/v1alpha1
kind: Traceflow
metadata:
  name: test-trace
spec:
  source:
    namespace: default
    pod: frontend-pod
  destination:
    namespace: default
    pod: backend-pod
  packet:
    ipHeader:
      protocol: 6
      ttl: 64

# Enable eBPF acceleration in Antrea
apiVersion: antrea.tanzu.vmware.com/v1alpha1
kind: AntreaConfig
metadata:
  name: antrea-config
  namespace: kube-system
spec:
  features:
    eBPF: true
            

Performance Comparison

Performance varies significantly between CNI plugins. Here's a general comparison of key metrics:

Metric	Calico (eBPF)	Calico (iptables)	Cilium	Flannel (VXLAN)	Flannel (host-gw)	Weave
Throughput	Near Native	Good	Near Native	Good	Excellent	Good
Latency	Very Low	Low	Very Low	Medium	Very Low	Medium
Resource Usage	Medium	High	Medium	Low	Low	Medium
Network Policy	Full	Full	Advanced (L7)	None	None	Limited
Observability	Good	Good	Excellent	None	None	Basic
Complexity	Medium	Medium	High	Low	Low	Low

Performance Note: Performance benchmarks vary based on cluster size, workload, and configuration. Always test with your specific workload patterns. Flannel host-gw provides near-native performance but only works on the same subnet. Calico eBPF and Cilium provide excellent performance with advanced features.

How to Choose the Right CNI

For Production Clusters

Calico is the most proven production choice with full NetworkPolicy and BGP routing. Cilium is excellent for performance and security with eBPF.

Production, enterprise

For Security-Focused Workloads

Cilium provides identity-based security, L7 policies, and service mesh integration. Calico offers comprehensive NetworkPolicy.

Security-critical

For High Performance

Cilium with eBPF, Calico with eBPF, or Flannel host-gw (on same subnet) provide the best performance.

Performance-critical

For Development/Testing

Flannel is the simplest and quickest to set up. Weave is also easy with built-in DNS.

Dev, test, prototyping

For Cloud-Native Environments

Cilium is cloud-native with eBPF. Calico works well in all cloud environments. Consider cloud provider-specific CNIs for managed clusters.

Cloud, multi-cloud

For Service Mesh Integration

Cilium has built-in service mesh. Calico integrates with Istio. Both support mTLS and traffic management.

Service mesh

Recommendation: For most production clusters, start with Calico (the proven standard). If you need eBPF performance and advanced security, choose Cilium. For simple setups, Flannel is excellent. Test with your specific workloads before making a final decision.

Frequently Asked Questions

Which CNI is the fastest?

Performance depends on the configuration. Flannel host-gw (same subnet) is near-native. Cilium with eBPF and Calico with eBPF provide excellent performance with low latency. VXLAN-based CNIs have more overhead. Test with your specific workloads.

Does Flannel support NetworkPolicy?

No, Flannel does not support Kubernetes NetworkPolicy natively. If you need network policies, consider Calico, Cilium, or Antrea. You can also use Flannel with a separate policy engine like Calico's policy-only mode.

What is eBPF and why does it matter?

eBPF (extended Berkeley Packet Filter) allows running sandboxed programs in the kernel. For CNIs, eBPF enables high-performance packet processing, observability, and security without the overhead of iptables. Cilium and Calico (in eBPF mode) leverage eBPF for performance.

Can I change CNI after cluster creation?

Yes, but it's a disruptive operation. You need to drain nodes, remove the old CNI, install the new CNI, and restart nodes. Test the migration in a non-production environment first. Some providers (like GKE, EKS) don't allow CNI changes.

What's the difference between overlay and native routing?

Overlay routing (VXLAN, IP-in-IP) encapsulates packets between nodes. Native routing (BGP, host-gw) routes directly. Native routing has less overhead but requires nodes to be on the same network. Overlay is more flexible for multi-cloud and multi-subnet environments.

Which CNI is best for multi-cloud?

Cilium (with eBPF) and Calico (with BGP) work well across cloud environments. Flannel with VXLAN is also multi-cloud compatible. Consider using a CNI that supports overlay networking for cross-cloud communication.

Does the CNI choice affect service mesh?

Yes. Cilium has built-in service mesh. Calico integrates with Istio. Flannel doesn't support service mesh natively. For service mesh, choose Cilium or Calico for better integration and traffic management capabilities.

How do I monitor CNI performance?

Use Prometheus metrics from the CNI. Calico provides metrics via Typha. Cilium provides Hubble for observability. Weave has built-in monitoring. Use tools like Prometheus, Grafana, and cilium-cli for performance monitoring.

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Choosing the right CNI plugin is one of the most important decisions for your Kubernetes cluster. Consider your requirements for performance, security, features, and operational complexity, and test thoroughly before deploying to production.