Azure Kubernetes Service (AKS) has become the backbone of many enterprise-scale containerized workloads, offering developers and operations teams a streamlined platform to deploy, manage, and scale applications. At the heart of AKS lies network infrastructure, a crucial component that defines connectivity, performance, and security. Understanding the different networking models, configurations, and best practices in AKS ensures that workloads remain resilient, compliant, and highly available.

In this guide, we explore networking in AKS, from fundamental principles to advanced technical configurations, empowering organizations to optimize their cloud-native environments.

Core Concepts of AKS Networking

Cluster Networking Model

When deploying AKS clusters, networking must be carefully defined. AKS supports two primary models:

1. Kubenet Networking
   • Default lightweight network model.
   • Pods receive IPs from a private range internal to the cluster.
   • Outbound connectivity is achieved through Network Address Translation (NAT).
   • Less complex but requires routing setup for pod-to-pod communication across nodes.
2. Azure CNI (Container Networking Interface)
   • Pods are assigned IP addresses directly from the virtual network (VNet).
   • Full integration with Azure VNets.
   • Simplifies communication with external resources but requires careful IP address planning.

Networking Components in AKS

• Virtual Networks (VNets): Provide logical network segmentation.
• Subnets: Allocate IP ranges for nodes, pods, and services.
• Load Balancers: Handle external and internal traffic routing.
• Ingress Controllers: Manage HTTP/HTTPS routing with SSL termination.
• DNS Services: Enable service discovery within clusters.

Designing Virtual Networks for AKS

VNet and Subnet Planning

Proper VNet design is critical for scalable AKS infrastructure. We recommend:

• Assigning dedicated subnets for system nodes, user nodes, and pods.
• Using larger IP address ranges when adopting Azure CNI to prevent exhaustion.
• Reserving separate subnets for ingress controllers and application gateways.

Peering and Hybrid Connectivity

AKS clusters often require secure connections with on-premises systems or other VNets. This is achieved via:

• VNet Peering: Fast, private, and low-latency connections across VNets.
• VPN Gateway or ExpressRoute: Secure hybrid networking for enterprise workloads.
• Private Endpoints: Directly connect services like Azure SQL or Storage without public exposure.

Ingress and Egress Traffic Management

Ingress Traffic in AKS

To handle incoming requests, AKS leverages Azure Load Balancer and Ingress Controllers:

• Azure Standard Load Balancer: Supports both inbound and outbound connections.
• Nginx Ingress Controller: Popular choice for SSL termination, URL routing, and advanced traffic rules.
• Azure Application Gateway Ingress Controller (AGIC): Provides Layer 7 traffic management with WAF integration.

Egress Traffic in AKS

Outbound connectivity must be secured and controlled:

• NAT Gateway ensures stable outbound IP for applications.
• Azure Firewall provides advanced security and inspection for egress traffic.
• Custom Routes allow defining precise outbound traffic paths.

DNS and Service Discovery

CoreDNS in AKS

Every AKS cluster includes CoreDNS for internal service resolution. It translates Kubernetes service names into IP addresses, ensuring pod-to-pod communication remains seamless.

Private DNS Zones

When integrating with external or private resources, Azure Private DNS zones ensure consistent name resolution across VNets and hybrid connections.

Advanced Networking Features in AKS

Network Policies for Security

Kubernetes Network Policies define how pods communicate with each other. AKS supports:

• Azure Network Policies: Deep integration with Azure networking.
• Calico Network Policies: Flexible, open-source solution for granular security rules.

These policies allow administrators to:

• Block unnecessary east-west traffic.
• Enforce zero-trust networking.
• Align with compliance requirements.

Private Cluster Deployments

For high-security workloads, AKS offers Private Clusters, ensuring that the Kubernetes API server is accessible only within the VNet. This model prevents public internet exposure and enforces strict access control.

Dual-Stack Networking (IPv4 + IPv6)

Modern applications increasingly require dual-stack networking to support both IPv4 and IPv6. AKS supports dual-stack clusters, enabling:

• Extended addressing capacity.
• Improved connectivity for IoT and edge devices.
• Future-proofed infrastructure for evolving standards.

Integrating Security with AKS Networking

Azure Firewall and Network Security Groups (NSGs)

• Azure Firewall: Provides centralized security with stateful packet inspection.
• NSGs: Define inbound and outbound traffic rules at subnet or NIC level.

Together, these tools create layered defenses, protecting clusters against malicious traffic.

Web Application Firewall (WAF)

When paired with Application Gateway, WAF protects workloads against OWASP Top 10 vulnerabilities, including SQL injection and cross-site scripting.

Scaling and Performance Optimization

IP Address Management

In large clusters, IP exhaustion is a common issue. Mitigation strategies include:

• Using Azure CNI with Dynamic IP allocation.
• Segmenting pods across multiple subnets.
• Employing Overlay networking models where appropriate.

Load Balancer Optimization

• Use Standard Load Balancer for production workloads due to higher resiliency.
• Optimize backend pools and probe configurations for efficiency.

Monitoring and Troubleshooting

Leverage Azure Monitor and Container Insights to track:

• Pod-to-pod latency.
• DNS resolution performance.
• Load balancer health metrics.

Best Practices for AKS Networking

1. Plan IP ranges carefully before cluster deployment.
2. Use private clusters whenever possible for enhanced security.
3. Leverage ingress controllers for advanced Layer 7 traffic routing.
4. Implement network policies to enforce zero-trust security.
5. Integrate monitoring solutions to gain visibility into traffic flows.
6. Adopt hybrid networking patterns for enterprise workloads.
7. Regularly audit firewall and NSG rules for compliance.

Conclusion

A well-architected network infrastructure in Azure Kubernetes Service (AKS) is essential for running secure, resilient, and scalable containerized workloads. From choosing between Kubenet and Azure CNI, to implementing network policies, ingress controllers, and private clusters, every decision plays a crucial role in performance and security. By applying the best practices outlined here, organizations can unlock the full potential of AKS and future-proof their cloud-native applications.