Introduction
Kubernetes has become the cornerstone of cloud-native infrastructure. While its orchestration capabilities are widely recognized, Kubernetes networking remains one of its most complex yet crucial pillars — especially in enterprise-grade deployments.
If you're running production workloads in Azure Kubernetes Service (AKS), the choice of networking plugin significantly impacts scalability, security posture, observability, and compliance. Enter Azure CNI and Cilium, a pairing that combines Azure-native networking integration with cutting-edge, eBPF-powered security and visibility.
Azure CNI: High-Performance VNet Integration
Azure CNI is not just a network plugin—it’s the bridge between AKS and Azure’s virtual networking fabric.
How It Works:
- Each pod gets an IP address from the Azure VNet subnet (no NAT).
- This allows direct, routable access between pods and other Azure services (e.g., Azure SQL, Private Endpoints, etc.).
- Network Security Groups (NSGs), Route Tables, and firewalls apply natively.
Benefits:
- Predictable IP Addressing (no overlay needed)
- Hybrid connectivity ready
- Works seamlessly with Azure Firewall, Azure Application Gateway, and Private Link
However, Azure CNI alone lacks advanced features like application-layer security, identity-based policies, and deep observability. This is where Cilium steps in.
Cilium: eBPF-Powered Networking & Security
Cilium is a revolutionary Kubernetes networking and security project built on eBPF (extended Berkeley Packet Filter)—a Linux kernel technology that allows programmable, high-performance packet processing.
What Cilium Brings to AKS:
| Feature | Description |
|---|---|
| eBPF Networking | Replace iptables with eBPF for faster, more scalable packet filtering |
| L3/L4/L7 Network Policies | Apply granular access rules down to the API call level |
| FQDN-based Egress Control | Block/allow traffic to domains like *.github.com |
| Hubble Observability | Real-time network flow monitoring and service dependency visualization |
| Transparent Encryption | Encrypt pod-to-pod traffic with WireGuard, no app changes required |
Note: For using FQDN Filtering, L7 Network Policies, Container Network Observability, we need to enable advanced container networking services.
Why Azure CNI + Cilium Together?
- Azure CNI provides robust, native VNet integration
- Cilium enhances security and observability via eBPF
This duo creates a hybrid setup that’s ideal for regulated, performance-sensitive, production workloads.
Architecture Overview
Here’s what this combination looks like in practice:
Pods are directly IP-addressed within Azure VNet (Azure CNI), while Cilium runs as a daemonset/enforcer, applying security policies and exporting observability metrics
Zero Trust Security in AKS Using Cilium
The traditional perimeter firewall model is ineffective in Kubernetes. What you need is workload-level security — and that’s what Cilium delivers.
Security Capabilities:
- Identity-Aware Policies
Define rules like: "Allow frontend pods to call backend pods only if they use service account X" - FQDN Policies
Prevent data exfiltration by whitelisting external domains (e.g., allow only microsoft.com and github.com) - Protocol-Aware Filtering
Enforce that service X only allows HTTP GET to /api/* from certain pods — not just any TCP traffic. - Transparent Encryption
Secure east-west traffic inside your cluster using WireGuard-based encryption, with zero impact on apps.
Observability with Hubble: No More Blind Spots
Understanding how services communicate in Kubernetes is vital for debugging, auditing, and performance tuning. Cilium ships with Hubble, a distributed observability layer that runs natively on top of eBPF.
Features of Hubble:
- Service Dependency Graphs
- DNS Query Visibility
- L3–L7 Traffic Flows (who’s talking to whom)
- Dropped Packet Analysis
- Built-in Grafana/Prometheus Dashboards
Conclusion: Modernize Your Cluster Networking the Smart Way
The future of cloud-native networking is kernel-level, programmable, secure by default, and deeply observable.
By adopting Azure CNI with Cilium in AKS, you're not just provisioning connectivity — you're enabling:
- Zero-trust network enforcement
- Real-time application flow insights
- High-performance packet processing
- Resilience in a hybrid/multi-cloud environment
Microsoft