An Azure Kubernetes Service (AKS) private cluster ensures that your Kubernetes API server is completely isolated from the public internet. This architecture uses the Azure Container Networking Interface (CNI) to deploy both the control plane and the worker nodes inside a dedicated virtual network. Within this boundary, the API server is exposed only through a private endpoint instead of a public IP address. Consequently, clients must access the control plane using its automatically generated private IP because custom private FQDNs are not supported. This setup restricts administration capabilities strictly to users and systems located within the same virtual network or a peered network.
A system architecture diagram showing an AKS private cluster where the API server is accessed via a private endpoint inside a virtual network, with management traffic from a peered network and external ingress routed through an Application Gateway.
To maintain a secure environment, all associated resources like Azure Storage, Azure Key Vault, and Azure Container Registry must reside in the same virtual network or a peered network within the same region. You configure this by creating private endpoints for each of these resources to ensure no traffic leaks to the public internet. Integration with private DNS zones is required so that resource names resolve correctly to their private IP addresses within the virtual network. Additionally, you must assign a system-assigned managed identity to the workspace to allow secure authentication to private-only storage accounts. This establishes a trusted boundary where credentials and container images never cross into the public space.
Securing East-West traffic between workloads inside the cluster requires granular control over how pods communicate with each other. You can implement Kubernetes network policies using either the Azure engine or the Calico engine via Azure Network Policy Manager (NPM). These policies allow you to label pods and write specific ingress and egress rules to restrict unauthorized internal communication. At the host level, the system enforces these rules using Linux IPTables or Windows Host Network Service access control lists. Because the cluster uses Azure CNI, each pod receives its own virtual network IP address and immediately conforms to these active security policies.
Controlling North-South traffic involves managing how data enters and leaves the cluster from outside networks. You apply Network Security Groups (NSGs) and route tables directly to the subnets to enforce baseline network isolation. To filter and inspect outbound traffic, you can route egress connections through Azure Firewall or a network virtual appliance using user-defined routes (UDRs). For incoming web traffic, integrating Azure Application Gateway with a Web Application Firewall provides layer-7 routing, SSL termination, and protection against common web vulnerabilities. This combination of firewalls, application gateways, and custom routing ensures that all external traffic is strictly validated before reaching any cluster resources.
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An Azure Kubernetes Service (AKS) private cluster isolates the Kubernetes API server from the public internet by deploying the control plane and worker nodes inside a dedicated virtual network using Azure Container Networking Interface (CNI). The API server is exposed only through a private endpoint, requiring clients to access it via its private IP address from within the same virtual network or a peered network.
You secure East-West traffic between pods by implementing Kubernetes network policies using either the Azure engine or the Calico engine via Azure Network Policy Manager (NPM). These policies allow you to label pods and write specific ingress and egress rules to restrict unauthorized internal communication, which are enforced at the host level using Linux IPTables or Windows Host Network Service access control lists.
Resources like Azure Storage, Azure Key Vault, and Azure Container Registry must reside in the same virtual network or a peered network within the same region, configured with private endpoints. Integration with private DNS zones is required for correct name resolution, and you must assign a system-assigned managed identity to the workspace to allow secure authentication to private-only storage accounts.
You control North-South traffic by applying Network Security Groups (NSGs) and route tables to the subnets for baseline isolation. To filter egress traffic, you can route connections through Azure Firewall or a network virtual appliance using user-defined routes (UDRs), and for incoming web traffic, you can integrate Azure Application Gateway with a Web Application Firewall for layer-7 routing and protection.
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