Network Isolation for Azure Kubernetes Service (AKS)
Why Network Isolation for AKS is Important
Network isolation in AKS is a critical security measure that protects your containerized workloads from unauthorized access and potential attacks. In a Kubernetes environment, multiple applications and services often run on shared infrastructure, making it essential to control traffic flow between pods, nodes, and external networks. Proper network isolation helps meet compliance requirements, reduces the attack surface, and ensures that sensitive workloads remain protected from both internal and external threats.
What is Network Isolation for AKS?
Network isolation for AKS refers to the collection of technologies and configurations used to control and restrict network communication within and around your Kubernetes cluster. This includes:
• Network Policies: Kubernetes-native rules that define how pods communicate with each other and external endpoints
• Azure Network Security Groups (NSGs): Layer 4 filtering applied at the subnet or NIC level
• Private AKS Clusters: Clusters where the API server is accessible only through private endpoints
• Azure Firewall and Application Gateway: Additional layers for controlling ingress and egress traffic
• Virtual Network Integration: Deploying AKS within your own VNet for complete network control
How Network Isolation Works in AKS
Network Policies
AKS supports two network policy providers: Azure Network Policy and Calico. These policies allow you to define ingress and egress rules at the pod level using label selectors. By default, all pods can communicate with each other; network policies enable a zero-trust model where only explicitly allowed traffic is permitted.
Private Clusters
When you create a private AKS cluster, the Kubernetes API server receives a private IP address from your VNet. This ensures that management traffic between the API server and node pools traverses only the Microsoft backbone network, not the public internet. You can access the API server through Azure Private Link, VPN, or ExpressRoute connections.
Azure CNI vs Kubenet
Azure CNI assigns VNet IP addresses to pods, enabling them to use Azure networking features like NSGs and service endpoints. Kubenet uses a separate IP range for pods with NAT for external communication. Azure CNI provides better integration with Azure network security features.
Egress Control
You can control outbound traffic from AKS using Azure Firewall, NAT Gateway, or user-defined routes (UDRs). This prevents data exfiltration and ensures pods can only reach approved external destinations.
Key Configuration Options
• --enable-private-cluster: Creates a private AKS cluster
• --network-policy azure or calico: Enables network policy enforcement
• --network-plugin azure: Uses Azure CNI for VNet integration
• --outbound-type: Configures egress method (loadBalancer, userDefinedRouting, managedNATGateway)
• --api-server-authorized-ip-ranges: Restricts API server access to specific IP ranges
Exam Tips: Answering Questions on Network Isolation for AKS
1. Understand the difference between network plugins: Azure CNI provides full VNet integration with pod IP addresses from the VNet, while Kubenet uses overlay networking. Questions about NSG application to pods typically point to Azure CNI.
2. Know when to use private clusters: When scenarios mention sensitive workloads, compliance requirements, or restricting API server access from the internet, private clusters are usually the correct answer.
3. Remember network policy providers: Azure Network Policy supports only ingress rules, while Calico supports both ingress and egress policies. If a question requires controlling outbound pod traffic using Kubernetes policies, Calico is the answer.
4. Recognize egress control scenarios: When questions mention controlling outbound traffic, monitoring egress, or preventing data exfiltration, look for answers involving Azure Firewall with UDRs or NAT Gateway.
5. API server access control: For questions about limiting who can access the cluster management plane, look for authorized IP ranges for public clusters or Private Link for private clusters.
6. Default behavior matters: Remember that by default, all pods can communicate with each other. Network policies must be explicitly created and applied to restrict traffic.
7. Service endpoints and Private Link: When AKS needs to access Azure PaaS services securely, look for answers mentioning service endpoints or Private Link rather than public endpoints.