Cilium: The eBPF-based Networking, Security, and Observability for Kubernetes

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In a standard Kubernetes cluster, `kube-proxy` relies on `iptables` to route traffic to services. While effective for small clusters, `iptables` was never designed for the dynamic, high-churn environments of modern cloud-native applications. As the number of services and endpoints grows, the sequential rule evaluation of `iptables` introduces significant latency and CPU overhead.

Enter eBPF and Cilium

eBPF (Extended Berkeley Packet Filter) is a Linux kernel technology that allows custom programs to run safely within the kernel space without requiring kernel modifications or loading modules.

Cilium is an open-source project (now a CNCF graduated project) that uses eBPF to provide networking, security, and observability for Kubernetes workloads. By attaching eBPF programs to various hooks in the kernel (like network interfaces or system calls), Cilium can process packets incredibly fast, completely bypassing iptables.

Key Benefits of Cilium

1. Kube-Proxy Replacement: Cilium can completely replace kube-proxy, significantly reducing latency and CPU usage by using eBPF hash tables for routing instead of sequential iptables rules.
2. Advanced Network Policies: Beyond standard Kubernetes Network Policies (which only filter on IP and port), Cilium can enforce L7 (Application Layer) policies. You can restrict traffic based on HTTP paths, methods, or even Kafka topics.
3. Multi-Cluster Routing (Cluster Mesh): Cilium seamlessly connects multiple Kubernetes clusters, allowing pod-to-pod communication across different clusters and clouds.

Hubble: Unprecedented Observability

One of the standout features of Cilium is Hubble, its observability platform. Because Cilium operates at the kernel level via eBPF, it has deep visibility into every packet traversing the network.

Hubble provides:

• Real-time service dependency maps.
• Deep visibility into dropped packets (and why they were dropped).
• L7 metrics (e.g., HTTP response codes, latency percentiles) without needing a heavy sidecar proxy like Istio.

Getting Started

Deploying Cilium is straightforward, especially on modern Kubernetes distributions. For example, using the Cilium CLI:

cilium install
cilium status

You can then enable Hubble for immediate insights:

cilium hubble enable
cilium hubble ui

Conclusion

Cilium is rapidly becoming the standard for Kubernetes networking. Its eBPF-based architecture not only solves the performance bottlenecks of traditional networking but also provides next-generation security and observability out of the box. Whether you are building a high-scale multi-cluster environment or simply looking to improve network visibility, Cilium is a project worth exploring.