Q: Your AKS cluster running 800 pods experiences packet drops and elevated CPU softirq overhead because kube-proxy and Calico/Azure network policies maintain over 45,000 iptables rules. How do you migrate the cluster to Azure CNI powered by Cilium without downtime, and enforce Layer 7 eBPF network policies?
Architectural runbook for migrating Azure Kubernetes Service (AKS) clusters from legacy iptables-based Azure Network Policies to Azure CNI Powered by Cilium, unlocking high-scale eBPF filtering and observability.
#Azure #AKS #Cilium #eBPF #Network Policies #Kubernetes
🎙️ Candidate Opening & Architectural Context
"At 2,000 services across our AKS production footprint, iptables sequential rule evaluation created severe node CPU latency spikes during pod churn. We migrated to Azure CNI Powered by Cilium to leverage eBPF B-tree hash maps for O(1) packet processing."
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🛠️ Production Runbook & Step-by-Step Resolution
1️⃣
Provision AKS Cluster with Azure CNI Powered by Cilium
Deploy Cilium dataplane mode with overlay networking or pod subnet delegation:
- CLI Cluster Creation: Executed
az aks create --resource-group rg-prod --name aks-cilium-prod --network-plugin azure --network-plugin-mode overlay --network-dataplane cilium --pod-cidr 192.168.0.0/16. - Verify eBPF Datapath: Verified that Cilium agents run in DaemonSet mode and bypass kube-proxy iptables chains entirely.
Pro Tip: Azure CNI Overlay with Cilium bypasses Azure VNet IP exhaustion by assigning pod IPs from a private virtual CIDR rather than physical subnet IPs.
2️⃣
Enforce Layer 7 DNS & HTTP CiliumNetworkPolicy
Implement fine-grained egress filtering down to domain names and REST endpoints:
- FQDN Filtering: Applied
CiliumNetworkPolicyallowing pods to query specific external endpoints (e.g.,*.vault.azure.net) while blocking all unauthorized outbound egress. - HTTP Path Rules: Restricted inter-service communication to exact HTTP methods (e.g., only
GET /api/v1/orders, denying all POST/DELETE calls).
Pro Tip: Standard Kubernetes NetworkPolicies only operate at Layer 3/4 (IP and port). Cilium eBPF parses Layer 7 HTTP and DNS protocol envelopes natively.
3️⃣
Deploy Hubble UI & Distributed Flow Telemetry
Gain real-time deep network visibility and flow tracing without kernel overhead:
- Enable Hubble: Configured Hubble telemetry via
az aks update --resource-group rg-prod --name aks-cilium-prod --enable-cilium-dataplane. - Flow Inspection: Inspected live dropped flows via
hubble observe --verdict DROPPED --namespace paymentsto immediately identify misconfigured security policies.
Pro Tip: Hubble provides kernel-level packet inspection without sidecar proxy latency, slashing MTTR for network policy debugging from hours to minutes.
4️⃣
Execute Zero-Downtime Blue-Green Cluster Migration
Safely migrate production workloads from legacy iptables cluster to Cilium cluster:
- Dual-Ingress Sync: Bound Azure Front Door backends to both the legacy cluster (Blue) and Cilium cluster (Green).
- Gradual Traffic Shift: Shifted traffic 10% -> 50% -> 100% while monitoring pod CPU latency and Hubble TCP reset metrics.
- Decommissioning: Drained and safely deleted legacy iptables nodes after 72 hours of zero error telemetry.
Pro Tip: Because Cilium dataplane changes cannot be toggled in-place on existing live node pools, blue-green cluster swapping is mandatory.
💡 The Senior SRE Gold Nugget (Key Architectural Takeaway)
"Azure CNI Powered by Cilium replaces bottlenecked iptables rules with eBPF kernel maps, delivering O(1) packet throughput, L7 network security, and Hubble real-time network telemetry."
⚡ 60-Second Elevator Pitch Talking Points
- Provision AKS with Azure CNI Overlay and --network-dataplane cilium to eliminate iptables scaling bottlenecks.
- Enforce Layer 7 FQDN and HTTP method filtering using CiliumNetworkPolicy CRDs.
- Deploy Hubble to visualize real-time packet drops and microservice dependency graphs.
- Execute a controlled blue-green cluster migration via Azure Front Door to ensure zero downtime.
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