Why Cilium Is the Game-Changing Cloud‑Native CNI for Kubernetes

As applications evolve toward micro‑services and cloud‑native architectures, the rapid creation and destruction of instances cause IP addresses to change quickly, making traditional IP‑based firewall rules inefficient. Cilium, a cloud‑native networking solution in the Kubernetes ecosystem, uses Linux kernel eBPF technology to address pod communication, improve performance, and enhance security.

What Is Cilium

Cilium provides a simple flat Layer‑3 network and can operate across multiple clusters using native routing or overlay modes. Its core relies on eBPF, a revolutionary Linux kernel feature that injects powerful security, visibility, and control logic directly into the kernel.

Core Capabilities

Container Networking (CNI)

Overlay networking: uses VXLAN or Geneve encapsulation to create a virtual network across all hosts.

Native routing: leverages the Linux host routing table for higher performance.

Flexible routing options: supports L2 neighbor discovery and BGP for cross‑cluster connectivity.

Advanced Load Balancing

East‑west load balancing: efficiently routes traffic between services inside the cluster.

North‑south load balancing: uses XDP to accelerate inbound and outbound traffic.

High performance: eBPF hash tables enable scalable, low‑latency service routing.

Security Policies

Decouples security from IP addresses by using identities.

Provides multi‑layer protection, filtering traffic from L3 to L7.

Supports DNS‑based policies to control access by domain name.

Enables L7‑aware filtering for HTTP methods, paths, gRPC calls, etc.

Cilium Architecture and Key Components

Cilium Agent: runs on every node in the cluster.

Cilium Operator: a cluster‑wide component.

CNI plugin: integrates with Kubernetes.

Hubble: observability platform for network traffic.

Deploying Cilium

Install Cilium CLI

CILIUM_CLI_VERSION=$(curl -s https://raw.githubusercontent.com/cilium/cilium-cli/main/stable.txt)
CLI_ARCH=amd64
if [ "$(uname -m)" = "aarch64" ]; then CLI_ARCH=arm64; fi
curl -L --fail --remote-name-all https://github.com/cilium/cilium-cli/releases/download/${CILIUM_CLI_VERSION}/cilium-linux-${CLI_ARCH}.tar.gz{,.sha256sum}
sha256sum --check cilium-linux-${CLI_ARCH}.tar.gz.sha256sum
sudo tar xzvfC cilium-linux-${CLI_ARCH}.tar.gz /usr/local/bin
rm cilium-linux-${CLI_ARCH}.tar.gz{,.sha256sum}

Install Cilium

cilium install

Verify Installation

# Check that Cilium pods are running
kubectl -n kube-system get pods -l k8s-app=cilium
# Run connectivity test
cilium connectivity test

Using Helm

Helm offers the most flexible and customizable way to install Cilium, allowing you to configure all aspects to match your environment.

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

Network Modes

Cilium supports two network modes:

Overlay network : uses VXLAN or Geneve encapsulation; works with virtually any network infrastructure; only requires IP connectivity between hosts; default when installing Cilium.

Native routing : leverages the Linux host routing table; requires the network to route pod IPs; offers better performance with no encapsulation overhead; integrates with cloud routers and IPv6‑native infrastructures.

Enable Native Routing

helm install cilium cilium/cilium \
   --namespace kube-system \
   --set tunnel=disabled \
   --set ipv4NativeRoutingCIDR=<your-cidr>

CNI Chaining

Cilium can be linked via CNI to work alongside other CNI plugins, allowing integration with existing CNI implementations.

Network Observability

Since version 1.7, Cilium includes Hubble, an eBPF‑based observability tool that provides deep visibility into Kubernetes application and service traffic.

cilium hubble enable

Install the Hubble CLI to explore network traffic in depth:

curl -L --remote-name-all https://github.com/cilium/hubble/releases/latest/download/hubble-linux-amd64.tar.gz{,.sha256sum}
sha256sum --check hubble-linux-amd64.tar.gz.sha256sum
sudo tar xzvfC hubble-linux-amd64.tar.gz /usr/local/bin
rm hubble-linux-amd64.tar.gz{,.sha256sum}

Conclusion

Cilium is currently one of the coolest Kubernetes CNI plugins, offering advanced network policies, L7 traffic control, and a simple, efficient, and user‑friendly experience built on eBPF. Give it a try and experience its powerful capabilities.