Cilium

Cilium is a modern CNI plugin that uses eBPF (extended Berkeley Packet Filter) to provide high-performance networking, security, and observability for Kubernetes. It’s designed for cloud-native environments and offers advanced features like network policies, service mesh integration, and deep observability without requiring application changes.

What is Cilium?

Cilium leverages eBPF, a Linux kernel technology, to:

• Provide networking - Pod IP assignment and routing
• Enforce Network Policies - Kernel-level policy enforcement
• Enable observability - Deep visibility into network traffic
• Integrate with service meshes - Works with Istio, Linkerd, etc.
• Deliver high performance - Kernel-level processing for speed

eBPF Technology

eBPF allows programs to run in the Linux kernel:

Benefits:

• Kernel-level processing - No context switching overhead
• High performance - Faster than userspace solutions
• Security - Kernel-verified programs
• Flexibility - Programmable networking and security

Key Features

High Performance

Cilium’s eBPF-based architecture provides:

• Kernel-level processing - No userspace overhead
• Efficient packet handling - Optimized data paths
• Low latency - Minimal processing overhead
• High throughput - Can handle high traffic volumes

Network Policies

Cilium provides full Network Policy support:

• Kernel enforcement - Policies enforced in kernel
• High performance - No performance penalty
• Advanced features - Extended policy capabilities
• L7 policies - HTTP/API-level policies (optional)

Observability

Cilium provides deep observability:

• Flow visibility - See all network flows
• Metrics - Prometheus metrics
• Tracing - Integration with tracing systems
• Hubble - Cilium’s observability platform

Service Mesh Integration

Cilium can work with service meshes:

• Istio integration - Can replace Envoy sidecars
• Reduced overhead - Less resource usage
• Unified networking - Single networking layer

Installation

Using Helm

helm repo add cilium https://helm.cilium.io/
helm install cilium cilium/cilium \
  --namespace kube-system

Quick Install

# Install Cilium
cilium install

# Verify installation
cilium status

Configuration

Cilium can be configured via ConfigMap or Helm values:

# Cilium ConfigMap
apiVersion: v1
kind: ConfigMap
metadata:
  name: cilium-config
  namespace: kube-system
data:
  enable-ipv4: "true"
  enable-ipv6: "false"
  enable-bpf-masquerade: "true"
  enable-remote-node-identity: "true"

Network Policies

Cilium supports Kubernetes Network Policies plus Cilium Network Policies:

Kubernetes Network Policy

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: example-policy
spec:
  podSelector:
    matchLabels:
      app: web
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: api
    ports:
    - protocol: TCP
      port: 80

Cilium Network Policy (L7)

Cilium also supports L7 (HTTP/API) policies:

apiVersion: "cilium.io/v2"
kind: CiliumNetworkPolicy
metadata:
  name: l7-policy
spec:
  endpointSelector:
    matchLabels:
      app: api
  ingress:
  - fromEndpoints:
    - matchLabels:
        app: web
    toPorts:
    - ports:
      - port: "8080"
        protocol: TCP
      rules:
        http:
        - method: "GET"
          path: "/api/v1/users"

Hubble Observability

Hubble is Cilium’s observability platform:

Hubble Features

• Flow visibility - See all network flows
• Service dependency maps - Visualize service connections
• Security monitoring - Monitor policy violations
• Performance metrics - Track network performance

Using Hubble

# Install Hubble
cilium hubble enable

# Access Hubble UI
cilium hubble ui

Performance Characteristics

Cilium’s eBPF-based architecture provides:

• Lower latency - Kernel-level processing
• Higher throughput - Efficient packet handling
• Lower CPU usage - No userspace overhead
• Better scalability - Handles large clusters well

Use Cases

High-Performance Clusters

Cilium is ideal when performance matters:

• High-traffic applications
• Low-latency requirements
• Resource-constrained environments

Advanced Observability

When you need deep visibility:

• Security monitoring
• Performance analysis
• Troubleshooting network issues

Service Mesh Integration

When using service meshes:

• Reduce sidecar overhead
• Unified networking layer
• Better performance

Best Practices

1. Enable Hubble - Use Hubble for observability
2. Monitor eBPF programs - Monitor eBPF program performance
3. Use L7 policies wisely - L7 policies add overhead
4. Keep updated - Update Cilium regularly
5. Test performance - Benchmark network performance
6. Monitor resources - Track CPU and memory usage
7. Use Cilium policies - Leverage Cilium-specific features when needed
8. Document configuration - Document Cilium configuration
9. Plan for growth - Ensure Cilium can scale with cluster
10. Backup configuration - Backup Cilium resources

Troubleshooting

Installation Issues

1. Check kernel version: Cilium requires Linux 4.9+
2. Verify eBPF support: cilium status
3. Check node resources: Ensure adequate resources
4. Review logs: kubectl logs -n kube-system -l k8s-app=cilium
5. Verify CNI config: Check CNI configuration

Performance Issues

1. Check eBPF programs: Monitor eBPF program performance
2. Review metrics: Check Cilium metrics
3. Optimize configuration: Review and optimize config
4. Check node resources: Ensure adequate CPU/memory
5. Review policies: Complex policies may impact performance

Network Policies Not Working

1. Verify Cilium version: Ensure version supports policies
2. Check Cilium status: cilium status
3. Review policy syntax: Verify policy YAML
4. Test simple policy: Create basic policy to test
5. Check logs: Review Cilium agent logs

See Also

• CNI Plugins Overview - CNI plugin comparison
• Network Policies - Network isolation
• Service Meshes - Service mesh integration
• CNI Basics - Understanding CNI