Cilium: eBPF-Powered Networking, Security, and Observability for Kubernetes

Intro

If you’ve been running Kubernetes for a while, you’ve probably hit the wall with traditional networking and security approaches. iptables rules, sidecar proxies, and userspace network filters can get messy fast – and they don’t exactly scale gracefully. That’s where Cilium comes in.

Cilium is a CNI plugin that uses eBPF (extended Berkeley Packet Filter) to handle networking, security, and observability directly inside the Linux kernel. No sidecars. No complex iptables chains. Just fast, programmable kernel-level operations that make your cluster both safer and more performant. If you haven’t played with eBPF yet, this is a great way to see it in action.

What It Does

Cilium replaces traditional Kubernetes networking layers with eBPF programs that run inline in the kernel. It handles:

• Pod-to-pod networking (overlay or direct routing)
• Network policies (Kubernetes NetworkPolicy and beyond)
• Load balancing (service mesh integration, L3/L4/L7)
• Observability (traffic flows, latency, DNS, and HTTP metrics)
• Security (identity-based policies, transparent encryption, and API-aware filtering)

It uses a concept called Identity instead of IP addresses – each pod gets a security identity tied to its labels. Policies are written in terms of these identities, not static IPs, which makes them survive pod churn gracefully.

Why It’s Cool

The real magic is eBPF. Because Cilium runs in kernel space, it can inspect and filter traffic at wire speed without copying packets to userspace. This means:

• No sidecars needed. No Envoy, no Istio sidecar overhead. Service mesh capabilities (like mTLS and L7 policy) are built into the kernel.
• DNS-aware policies. You can write rules like “allow pods with label app=frontend to resolve api.server.com and only allow GET requests.” That’s powerful.
• Hubble. Cilium ships with a built-in observability layer (Hubble) that gives you full visibility into traffic flows, latency, and dropped packets. You get a service map and real-time metrics without extra tooling.
• Performance. Because it’s kernel-native, you see lower CPU usage and lower latency compared to iptables-based solutions, especially under high connection churn.

Use cases range from bare-metal