What is Cilium?

Cilium is an open-source networking and security layer for containers and micro-services that runs inside a Kubernetes cluster. It uses the Linux kernel’s eBPF technology to manage traffic, enforce policies, and provide visibility without needing extra network appliances.

Let's break it down

  • Open-source: Free for anyone to use, modify, and share.
  • Networking and security layer: A piece of software that controls how data moves between containers and protects them.
  • Containers and micro-services: Small, isolated pieces of an application that run together in a cloud environment.
  • Kubernetes cluster: A group of machines that run containers and manage them automatically.
  • eBPF (extended Berkeley Packet Filter): A powerful feature in the Linux kernel that lets programs run safely inside the kernel for fast packet processing and monitoring.
  • Manage traffic: Decide where data packets go.
  • Enforce policies: Apply rules like “only service A can talk to service B”.
  • Visibility: Show what’s happening with the network in real time.

Why does it matter?

Cilium makes container networking faster, more secure, and easier to understand, which helps developers and operators keep their cloud applications running smoothly and safely without adding complex hardware or software layers.

Where is it used?

  • Large e-commerce platforms that need to isolate and protect thousands of micro-services while keeping latency low.
  • Financial institutions running high-frequency trading apps where ultra-low network latency and strict security are critical.
  • Edge-computing deployments that run containers on many small devices and need a lightweight, programmable network stack.
  • Cloud-native SaaS providers that want detailed traffic observability to troubleshoot issues quickly.

Good things about it

  • High performance: eBPF runs in the kernel, giving near-native speed for packet handling.
  • Fine-grained security: Policies can be written per pod, per service, or even per API call.
  • Deep observability: Real-time metrics and flow logs without extra agents.
  • Kubernetes native: Integrates seamlessly with existing K8s tools and APIs.
  • Scalable: Works well from a few nodes up to thousands of nodes.

Not-so-good things

  • Steep learning curve: Understanding eBPF and Cilium’s policy language can be challenging for beginners.
  • Kernel compatibility: Requires a relatively recent Linux kernel; older distributions may not support all features.
  • Operational complexity: Debugging low-level networking issues may need specialized knowledge.
  • Resource overhead: While lightweight, the eBPF programs still consume CPU and memory, which can matter in very constrained environments.