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Cilium

Required knowledge for the CKS certification.

Cilium is an advanced networking, security, and observability platform for Kubernetes that leverages eBPF (Extended Berkeley Packet Filter) to provide high-performance networking, transparent encryption, network policies, and deep visibility into traffic flows.

It replaces traditional kube-proxy, CNI plugins, and service meshes with a modern, programmable data plane that integrates tightly with Kubernetes.

Usage​

1. Install Cilium​

Use the Cilium CLI to install it into your cluster:

cilium install

Check Cilium status:

cilium status

2. Define Network Policies with Cilium​

Example: Allow only frontend pods to access the backend.

apiVersion: cilium.io/v2
kind: CiliumNetworkPolicy
metadata:
  name: allow-frontend
spec:
  endpointSelector:
    matchLabels:
      app: backend
  ingress:
    - fromEndpoints:
        - matchLabels:
            app: frontend

Apply the policy:

kubectl apply -f allow-frontend.yaml

3. Enable Transparent Encryption​

Enable encryption between nodes using WireGuard or IPsec:

cilium config set enable-ipsec true

Or using Helm:

helm upgrade cilium cilium/cilium --set encryption.enabled=true

4. Observe Network Flows​

Use Hubble, Cilium's observability engine:

cilium hubble enable
cilium hubble ui

You can visualize:

  • Service-to-service communication
  • DNS queries
  • Allowed/denied flows
  • Identity and label-based flows

Best Practices​

  • Replace kube-proxy with Cilium to simplify architecture and reduce latency.
  • Use identity-aware network policies for more granular control than standard Kubernetes NetworkPolicy.
  • Enable Hubble to monitor and audit all traffic and security events.
  • Use transparent encryption to secure node-to-node traffic with zero changes to workloads.
  • Regularly test your policies using Cilium’s connectivity test suite.

Resources​