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Implementing “Burton” Network Segmentation in AKS

Introduction: Network segmentation is a cornerstone of a secure Azure Kubernetes Service (AKS) architecture. By isolating critical components and controlling traffic flows, you reduce the attack surface and enforce a Zero Trust stance. In this guide, we outline a “Burton” network segmentation approach for AKS – focusing on isolating the AKS control plane, segmenting workloads via Azure networking features, and leveraging Azure’s native security tools for auditing and enforcement. We will cover how to design Network Security Groups (NSGs), User-Defined Routes (UDRs), and Private Links to compartmentalize network access, as well as strategies for ingress/egress control, logging, and alerting. Azure-native services like Defender for Containers, Azure Policy, and diagnostic logging are integrated into this design for comprehensive monitoring and compliance. The recommendations here build on Microsoft’s AKS security baseline and reference architectures , ensuring industry best practices (e.g. PCI-DSS) are met.

1. Segmenting the AKS Control Plane from Other Infrastructure

Use Private AKS Clusters: Always prefer deploying AKS as a private cluster to isolate the Kubernetes API server from the public Internet . In a private cluster, the control plane’s API endpoint is exposed via an Azure Private Link endpoint in your virtual network (VNet) – meaning all communication between the AKS control plane and your node pools stays on private IPs . This prevents direct public access to the Kubernetes API. If a private cluster is used, ensure that the cluster is created with no public DNS for the API (set enablePrivateClusterPublicFQDN=false) so that even the DNS name of the API is not published publicly .

  • Authorized IP Ranges: If a private cluster is not feasible, at minimum restrict API access by enabling authorized IP ranges on the AKS API server . Only specific IPs (e.g. a jumpbox subnet or on-premises gateway) should be allowed to communicate with the control plane. This ensures that even the public API endpoint responds only to trusted sources.
  • Network Isolation of Control Plane: The control plane in AKS is managed by Azure (in a separate Azure subscription), but for private clusters Azure injects the API into your VNet. Treat the control plane endpoint as a highly sensitive asset: isolate it in a dedicated subnet if possible and do not allow other workloads to interact with it. Use Azure Policy to enforce that AKS clusters are private and deny the creation of public clusters in your environment .
  • Restrict Management Access: Do not deploy management tools on the cluster nodes themselves. Instead, use a separate admin subnet or jumpbox (bastion host) for Kubernetes administration. For example, you might have a locked-down jumpbox VM in a management subnet; this jumpbox can access the private AKS API endpoint. Lock down inbound access to the jumpbox via Azure Bastion or just-in-time access (no public IP) . The jumpbox’s outbound traffic should also follow the same egress restrictions as the cluster (forcing traffic through a firewall via UDR) .

Key points for control plane segmentation: Deploy private clusters to keep the AKS API on internal IPs; disable any public endpoints or DNS. Use authorized IP ranges if you must expose the API, and combine that with RBAC for strict control . Place admin tools on a separate secured subnet (or use Azure Bastion) rather than allowing direct access to node VMs. This ensures the AKS control plane is effectively segmented from other networks and the Internet, reducing the risk of unauthorized access or data exposure.

2. Enforcing Audit Controls on Network Traffic and API Interactions

A strong segmentation strategy must be accompanied by equally strong audit controls to monitor and record what’s happening on the network. Implement logging and monitoring at each layer to capture traffic flows and API calls, which is critical for detecting suspicious activity and proving compliance.

  • Kubernetes API Audit Logs: Enable audit logging for the AKS control plane. In AKS, you can do this by configuring Diagnostic Settings on the cluster resource to collect kube-audit and kube-audit-admin logs . These logs provide a chronological record of calls made to the Kubernetes API server (e.g. kubectl commands, deployments, etc.) and are invaluable for investigating security events. Send these audit logs to a Log Analytics Workspace or SIEM for retention and analysis . For example, Azure Monitor can ingest the logs (they appear in the AzureDiagnostics table) so you can run queries to answer “who did what, when”. Defender for Containers (an Azure Defender plan) actually relies on these audit logs for threat detection, so turning them on not only creates an audit trail but also enables advanced analytics .
  • Network Flow Logs: At the Azure network level, enable NSG flow logs and Azure Firewall logs to audit network traffic. NSG flow logs will record which flows are allowed or denied by your NSG rules. These can be exported to Azure Storage or Log Analytics for analysis. Similarly, if using Azure Firewall, enable Azure Firewall diagnostics to log all accepted/denied flows and DNS lookups. Consolidating these logs allows you to verify that segmentation rules are working as intended and that no unexpected traffic is bypassing your controls.
  • Azure Monitor and Alerts: Leverage Azure Monitor to set up alerts on the above logs. For example, you can create alerts for unexpected network activities (such as a surge in denied NSG traffic, which could indicate a port scan or malware trying to exfiltrate) or for specific Kubernetes API actions (e.g. alert if a new ClusterRoleBinding is created, as this could broaden access). Azure Monitor Alert rules or a connected SIEM (like Microsoft Sentinel) can continuously watch the log streams. All critical network devices (firewalls, gateways) and the AKS service should send logs to a central log store for correlation.
  • Regular Rule Reviews: Implement a process to periodically review and audit all network segmentation rules. Azure’s PCI compliance guidance suggests reviewing firewall and router rule sets at least every six months . In practice, this means reviewing Azure Firewall rules, NSG rules, Kubernetes Network Policies, etc., to ensure they are still necessary and optimal. Remove or tighten any rules that are overly permissive or no longer needed (for example, if a service was decommissioned, its network allow rules should be removed). Document any changes and maintain an updated network diagram showing all connections into and out of the AKS environment – this documentation itself is part of audit controls and is required in regulated environments.
  • Data Protection and Privacy: Ensure that sensitive network information is not exposed in logs or monitoring outputs unnecessarily. For instance, scrub or protect any logs that might reveal private IP addresses or DNS names when sharing data outside the ops team . Use role-based access for log data so that only authorized security personnel can view detailed network logs.

In summary, enable comprehensive logging at the cluster and network levels, and actively monitor those logs. By doing so, you create an audit trail for every significant network interaction – from API calls to connection attempts – which is crucial for forensic analysis and compliance verification. Azure provides the plumbing (via diagnostic settings and Monitor) to gather these signals, but it’s up to your team to configure and regularly review them.

3. Designing NSGs, UDRs, and Private Links for Segmentation of Workloads

Proper segmentation in AKS requires a combination of Azure virtual network controls and Kubernetes-aware controls. Here we design network segmentation such that workloads and critical services are isolated in their own trust zones. Key Azure features to use are Network Security Groups (NSGs) for access control, User-Defined Routes (UDRs) (often combined with an Azure Firewall) for traffic routing, and Private Link for restricting service endpoints. Below, we outline how to use each of these in the AKS context:

  • Network Security Groups (NSGs): NSGs act as virtual firewalls at the subnet or NIC level, allowing or denying traffic based on source/dest IPs, ports, and protocols. In an AKS deployment, apply NSGs to the subnet(s) hosting your node pools. The NSG rules should by default deny all inbound traffic from untrusted networks and allow only required flows:

    • Block External Inbound: Ensure no unsolicited inbound traffic from the Internet can reach pods or nodes. Since we do not assign public IPs to AKS nodes, this primarily means controlling flows from other Azure networks. For example, you might allow only the IP of an Azure Application Gateway (acting as ingress WAF) to reach the AKS ingress controller’s NodePort range, and block anything else . Also block management ports like SSH to nodes – in the reference design, NSGs on the node subnet deny all SSH (TCP 22) access attempts entirely .
    • Allow Required Internal Flows: Permit internal traffic that is necessary. This includes traffic from the nodes to the control plane (AKS service tag). Microsoft documents the specific service tags or FQDNs required for AKS; for instance, allow node subnet -> Azure Kubernetes Service (service tag) on TCP 443 for cluster management traffic . Also allow node-to-node communication as needed (or use Kubernetes policies for pod-to-pod). If your cluster needs to reach certain internal services (e.g., a database in a different subnet), whitelist only that subnet or service IP range on the needed port.
    • NSGs on Other Subnets: Likewise, apply NSGs on any subnet containing a critical service (such as a database or Azure Cache for Redis) to only allow access from the AKS subnet or other authorized subnets. This double-layer (NSG on source and destination) ensures robust isolation. For example, an Azure SQL database private endpoint might be in a subnet that only allows traffic from the AKS node subnet on the required SQL ports.
    • Egress Rules: While Azure Firewall (discussed below) will handle most egress control, you can also use NSG outbound rules to provide an extra layer of defense. For instance, you could put a “Deny Internet” outbound rule on the AKS subnet to block any direct internet traffic that somehow bypasses the firewall route (defense-in-depth). NSG flow logs will show if any rule is hit, which aids in auditing.

  • User-Defined Routes (UDRs) and Azure Firewall: By default, subnets send unknown outbound traffic directly to the Internet in Azure. To segregate and inspect egress from AKS, you’ll use a UDR on the AKS node subnet that forces traffic to a firewall (Azure Firewall in a hub network, or a third-party NVA). In the hub-spoke model, the AKS cluster lives in a spoke VNet peered to a hub VNet where an Azure Firewall resides. A UDR in the AKS subnet can direct 0.0.0.0/0 (and any other needed address prefixes) to the firewall’s private IP . Azure Firewall will then proxy or drop traffic based on its rules:

    • Allow Only Essential Egress: On Azure Firewall, define whitelisting rules for egress. For example, allow HTTPS traffic from the AKS nodes to specific FQDNs: the AKS control plane FQDNs (if public cluster), your container registry (e.g. \<myregistry>.azurecr.io), Microsoft patch servers, and any external APIs that your workloads need . Everything else should be denied by default. Azure Firewall supports FQDN tags and application rules, which you can leverage (e.g. an application rule to allow AzureContainerRegistry tag, which covers all *.azurecr.io endpoints). This tightly controls outbound calls – crucial for preventing data exfiltration or malware call-backs.
    • Logging and Threat Intel: Azure Firewall has built-in Threat Intelligence based filtering – you can configure it to alert or block traffic to known malicious IPs. This adds an additional segmentation layer: even if a pod is compromised and tries to reach a known bad actor, the firewall can block it. Be sure to enable Firewall logs for visibility. Microsoft’s guidance prefers Azure Firewall over a simpler NAT gateway for this reason – you get full traffic inspection and logging for compliance .
    • Routing Internal Traffic: UDRs can also ensure that traffic between the AKS subnet and other internal subnets (or on-prem networks via ExpressRoute/VPN) goes through a firewall or specific path. This allows monitoring and controlling even East-West traffic. For instance, if the AKS workload needs to call an API in another spoke VNet, you might route that VNet’s address range via the firewall as well, where you can apply rules. (Alternatively, use peering with NSG rules to restrict as discussed.) The main idea is no route from AKS goes uncontrolled – every path either stays within the VNet (pod-to-pod or pod-to-node, which Kubernetes network policy can handle) or hits a firewall for policy enforcement.

    • Private Link for Azure Services: Use Azure Private Link to access Azure PaaS services (like storage accounts, Key Vault, Azure SQL, Container Registry, etc.) via private endpoints in your VNet instead of over the public Internet. This is an important aspect of segmentation: it ensures even traffic to “external” services remains within your trusted network boundary. Key implementations for AKS:

    • Container Registry: If your AKS pulls images from Azure Container Registry (ACR), enable ACR’s private endpoint in the AKS VNet. Then configure ACR’s firewall to allow access only from that private endpoint (and perhaps your build agents’ network) . This means the cluster nodes will not reach out to ACR’s public IP at all – they go through the Private Link. In addition, the NSG/Firewall rules can enforce that the cluster only talks to ACR’s private IP, not any external registry.

    • Key Vault and Others: Similarly, use private endpoints for any Key Vault that the cluster accesses (for storing secrets, TLS certificates, etc.). In the AKS baseline architecture, Key Vault is firewalled to allow only the AKS subnet via its Private Link . Private DNS zones are used so that the standard DNS names (like myvault.vault.azure.net) resolve to the private IP within the VNet . This way, when, say, an ingress controller pod requests a TLS cert from Key Vault, it stays on the VNet. Other Azure services to consider for Private Link: Azure Monitor (logs), Azure Storage (if used by the app), databases, etc. In short, eliminate any requirement for the AKS workloads to use public IP endpoints for Azure services.
    • In-Cluster Services: For services that are internal to your cloud (e.g., an API running in another AKS or VM), consider connecting via VNet peering or Private Link Service endpoints, rather than going out and back in through public IPs. This keeps traffic internal and controllable.

Subnet Design: It’s common to use separate subnets for different components even within the AKS environment. For example, you might have: one subnet for the AKS node pools, another for an Application Gateway (ingress WAF), and others for any integrated services (like a subnet for private endpoints). This subnet separation combined with NSGs/UDRs allows you to enforce that, for instance, the App Gateway can talk to the AKS subnet (on specific ports) but nothing else can. Avoid deploying non-related resources in the AKS node subnet. The AKS subnet should be dedicated to the cluster nodes and necessary endpoints. This makes it easier to reason about NSG rules and reduces risk of cross-contamination.

Kubernetes Network Policies: While NSGs and Azure networking handle traffic to/from the cluster, Kubernetes network policies (such as Azure Network Policy or Calico) should be used for pod-to-pod (micro)segmentation within the cluster. For example, if you have multiple applications or microservices on the cluster, you can write NetworkPolicy objects that only allow necessary communication (e.g., allow the frontend pod to talk to the backend pod on port 5432, but deny all other cross-namespace traffic). This is critical for limiting lateral movement inside the cluster if one pod is compromised . Be sure to enable a network policy engine when creating the AKS cluster (Azure CLI has --network-policy flag), since it cannot be enabled post-creation . Azure’s recommendation is to use Azure Network Policy with Azure CNI for a fully supported solution , though Calico is an option for more complex policy requirements.

By combining NSGs, UDR+Firewall, Private Link, and network policies, you achieve layered segmentation:

  • The Azure VNet layer guards access to and from the cluster subnet (with NSGs controlling flows and UDRs routing egress through security chokepoints).
  • The Private Link ensures that even egress to Azure services stays “inside” your approved boundary (no exposure to public network).
  • The Kubernetes layer (NetworkPolicy) locks down traffic between pods and services at the application level.

This multi-tier segmentation contains breaches: even if an attacker compromises a pod, NSGs and network policies limit where it can go (it can’t reach your database or control plane), and the firewall limits external calls (with logging to alert you) . Each mechanism plays a role without relying on any single point of defense.

4. Strategies for Ingress/Egress Control, Logging, and Alerting

Controlling how traffic enters and leaves your AKS cluster is vital for security. Ingress (incoming traffic) should be funneled through well-defended points (with web application firewalls and filtering), and egress (outgoing traffic) should be tightly restricted to prevent data leaks and callback attacks. In tandem, you need robust logging of these ingress/egress points and active alerting on suspicious events. Here we outline a strategy:

Figure: Segmented AKS network with hub-spoke topology – All ingress from the public internet is funneled through a Web Application Firewall (WAF) in the spoke (AKS) network, and all egress from AKS is routed through an Azure Firewall in the hub network . Green arrows show user-initiated requests/responses, and orange arrows show cluster-initiated egress traffic and responses (e.g. calls to external APIs). Private endpoints (not shown) would similarly reside in the spoke to keep traffic internal.

  • Ingress Control via DMZ/WAF: Do not expose AKS services directly to the internet. Instead, establish a DMZ or entry point in front of the cluster. A common pattern is to use Azure Application Gateway with WAF as the ingress controller’s frontend. In this design, your AKS services use internal LoadBalancers (accessible only within the VNet) and the Application Gateway (in the same VNet or peered) routes external HTTP(S) traffic to those internal endpoints . The Application Gateway’s WAF filters and blocks malicious traffic (SQL injection, XSS, etc.) before it even reaches Kubernetes. Only the WAF’s public IP is exposed; the AKS API server and nodes are not publicly reachable. This aligns with best practices to “implement a DMZ to limit inbound traffic to only authorized services/ports” .

    • TLS Termination and End-to-End Encryption: It’s recommended to terminate TLS at the WAF (so it can inspect payloads) and then re-encrypt when forwarding to AKS. The AKS baseline uses end-to-end TLS: client->WAF (TLS), WAF->AKS ingress controller (TLS) . This ensures no clear-text traffic on the wire, even inside the VNet. Certificates can be stored in Key Vault and accessed via Private Link as described earlier . Ensure only strong ciphers and protocols are allowed for TLS (for example, restrict Application Gateway to TLS 1.2+ and a known-good cipher suite) .
    • Alternative Ingress Options: In some cases, you might use a simpler NGINX ingress controller (running inside AKS). If so, use an internal Azure Load Balancer for that ingress and put an external layer (like an Azure firewall or reverse proxy) in front of it to handle internet traffic. Another option is Azure Front Door or Azure Application Proxy for publishing apps securely. The principle remains: external traffic should hit a controlled, monitored point in Azure (with WAF/Firewall capabilities) before reaching the cluster.
    • Limit Ports and Protocols: Only allow necessary ports on the ingress path. For a web app, this might be just 443/TCP. If you have other services (say gRPC or SSH jump), consider using VPN or ExpressRoute instead of exposing them. Leverage NSGs to enforce that, for example, only the App Gateway subnet can talk to the AKS subnet on the ports your services listen on . By default, Kubernetes uses NodePort range (e.g. 30000-32767) for Service traffic – you can limit allowed inbound to those if using NodePort. If using AGIC (Application Gateway Ingress Controller), the App Gateway directly addresses pod IPs and those communications occur internally.

  • Egress Control and Internet Access: As discussed in section 3, egress from AKS should be funnelled through an Azure Firewall (or equivalent). This ensures that even if a workload tries to reach out to the internet, it must go through the firewall’s policies. Configure the firewall in whitelist mode – allow only known endpoints and deny all else . Common allowed egress in an AKS cluster includes: AKS control plane (for heartbeats, metrics, etc.), Azure services (Container Registry, Key Vault, Azure Monitor), security updates, and any third-party API the app needs. Everything else (e.g., arbitrary web access) should be blocked. This not only prevents malicious exfiltration but also reduces the risk of pods downloading malware.

    • DNS and NTP: Ensure your cluster nodes can resolve DNS in a segmented way. Use Azure Private DNS for private endpoints, and possibly restrict DNS to an internal DNS server or Azure Firewall’s DNS proxy, so that even DNS queries are monitored. Similarly, time sync (NTP) should use internal sources if possible or allow only to known NTP servers.
    • No Direct Internet on Nodes: The AKS node VMs should not have public IPs, and they shouldn’t bypass the firewall. Microsoft guidance explicitly says to avoid public IPs on nodes and use private cluster and private endpoints for all interactions . This way, the only egress path is through your controlled network.

  • Logging & Monitoring Ingress/Egress: Both the Application Gateway/WAF and Azure Firewall produce detailed logs. Enable WAF logs to see malicious request patterns and Firewall logs for allowed/denied traffic. These logs can be fed to Azure Monitor. For example, WAF logs might show repeated SQL injection attempts which you could alert on. Azure Firewall logs will show if any node tried to access an IP that is not allowed (hitting a default deny rule).

    • Use Azure Monitor Network Insights or Azure Sentinel to visualize these flows. You can map what connections are happening and verify they match expected patterns. Anomalies (like a database in one region suddenly getting traffic from an AKS cluster in another region that normally doesn’t communicate) can be spotted through log analytics.
    • Consider enabling Azure Monitor for containers (Container Insights) on the AKS cluster. While this is more about container health logging, it can complement security logging by capturing container stdout/stderr and metrics – sometimes a compromise might be spotted by unusual application logs or spikes in network throughput, which these tools can flag. Note that sending these monitoring logs can also be done via Private Link (Azure Monitor Private Link Scope) so that even the telemetry doesn’t egress publicly .

  • Alerting: Set up alerts on critical log events. For example:

    • Firewall alerts: if the firewall blocks traffic to a certain banned IP (could indicate a compromised pod trying to phone home) – trigger an alert to security teams.
    • WAF alerts: if the WAF sees a high severity rule triggered (like an attempted remote code execution in an HTTP request), alert the application security team to investigate that client/IP.
    • Kubernetes audit log alerts: if a new Kubernetes namespace is created or a new external LoadBalancer service appears (which should not happen in a tightly controlled environment without change control), send an alert. Azure Policy can also be used in audit mode to flag these events (e.g., creation of a service of type LoadBalancer could violate a policy that restricts that, generating a compliance event).
    • Use of Azure Defender for Cloud: Azure Defender for Containers (discussed more in next section) will automatically generate alerts for certain suspicious behaviors in AKS. For instance, it can alert on cryptocurrency mining activities, suspicious container file system changes, or known exploits. Make sure these alert rules are enabled, and have an incident response plan tied to them. Some alerts may involve egress anomalies – e.g., a pod connecting to an IP with bad reputation – which ties back to egress control.
    • Testing the Controls: Periodically test your ingress/egress rules to ensure they work. For ingress, attempt to hit a blocked port from an external source and confirm it’s dropped. For egress, try to wget/curl a benign site like example.com from a pod – you should see it blocked. Such tests (possibly automated as part of security reviews) ensure that any drift in NSGs or firewall rules is caught.

Summary of Ingress/Egress Strategy: All inbound user traffic goes through a secure frontend (WAF/Gateway) where it’s inspected and then forwarded internally over a private channel to AKS . All outbound traffic from AKS goes through a controlled egress point (firewall) where it’s filtered and logged . This dual approach creates a two-way shield around the cluster. Logging at both points and alerting on suspicious patterns turn your segmented network into an active defense system, not just static walls.

5. Azure-Native Security Tools: Defender for Containers, Azure Policy, Diagnostic Settings

Microsoft provides a rich suite of security tools that integrate with AKS – you should use these to enforce and monitor your network segmentation policies:

  • Microsoft Defender for Containers (formerly Defender for Kubernetes): This is a cloud-native container security solution in Defender for Cloud that you can enable on your AKS cluster. When enabled, Defender will continuously monitor the cluster’s activity and configuration. Key benefits in context of segmentation and security:

    • Threat Detection: Defender for Containers provides real-time threat protection by analyzing Kubernetes audit logs and looking for suspicious patterns . For example, it can detect if someone is running kubectl port-forward or if a deployment is created that violates best practices. It generates alerts for these events, which appear in the Defender for Cloud dashboard or can be forwarded to a SIEM. Because it looks at control plane logs, it can notice network-related events too (e.g. a normally internal-only Service being exposed as NodePort).
    • Host Security Integration: It also can monitor the AKS node VMs for suspicious processes (this may require also enabling Defender for Servers for full host-level protection) . If an attacker somehow got into a node and started port scanning or opening reverse shells, Defender could flag that behavior.
    • Vulnerability Management: Defender for Containers includes vulnerability scanning of images (through integration with ACR) and can check your cluster setup against known benchmarks (like misconfigured network policies or privileged containers). While this is more config-management, it complements network segmentation by ensuring, for instance, that no workload is running as root (which could be more dangerous if network segmentation is breached).
    • Exposure Management: It specifically looks for things like exposed dashboards or common misconfigurations in Kubernetes that could lead to segmentation failures (for example, an open service that shouldn’t be open) . Microsoft’s security researchers constantly update the analytics with new threats and attack patterns, which means your cluster benefits from broad threat intelligence .
      • Enabling Defender for Containers is typically as easy as turning on the plan in Defender for Cloud for that subscription and ensuring the cluster has the necessary extension/agents. It’s an essential guard for a production AKS cluster, adding an layer of intelligent monitoring on top of your manual network rules.

    • Azure Policy for AKS: Azure Policy lets you apply governance rules at scale. Microsoft provides a built-in policy initiative for AKS as part of the Azure Security Benchmark and Defender for Cloud recommendations . By enabling Azure Policy on your AKS clusters (which installs the Gatekeeper admission controller), you gain two things:

    • Preventive Controls: You can deny or modify non-compliant resources in the cluster. For example, you can enforce a policy that no service of type LoadBalancer is created in a given environment (so developers can’t accidentally expose an app publicly), or a policy that requires every ingress to use the internal SKU (no public IP) . You can also block pods from running in privileged mode, or ensure all pods have network policies attached, etc. These policies help maintain segmentation by preventing misconfigurations that would break your network isolation.

    • Audit and Compliance: Azure Policy will audit existing resources against rules. For instance, a policy can audit that AKS clusters are Private (and flag any public cluster), or audit that NSGs are present on subnets, or that no subnet allows broad “ANY” traffic. In Defender for Cloud, the Azure Security Benchmark includes many such checks (like “AKS clusters should not allow privileged containers” or “Subnet NSGs should restrict inbound traffic”). Use these to get continuous compliance reporting . Non-compliant items show up as recommendations for remediation.
      • Azure Policy for Kubernetes (via OPA Gatekeeper) is integrated directly – it will generate Kubernetes events for enforcement and can even be configured to block deployments that violate rules . All policy decisions are logged, which contributes to your auditing. For example, if someone tries to create a public LoadBalancer service and it’s denied by policy, that is logged (and you could alert on that event, since it might indicate either a mistake or a deliberate attempt to bypass security).

    • Diagnostic Settings & Monitoring Configuration: Ensure that Diagnostic Settings are turned on for all relevant Azure resources in the AKS deployment. We discussed enabling it for the AKS resource (to get control plane logs). Similarly, enable diagnostic logs for:

    • Azure Firewall: send Firewall logs and metrics to Log Analytics.

    • Application Gateway: send access logs, performance logs, and Firewall logs.
    • NSGs: NSG flow logs (this requires sending to a storage account or Log Analytics via Traffic Analytics).
    • Key Vault, ACR, etc: any service that provides logging of access or firewall events – enable those (e.g., Key Vault will log firewall blocks if someone tried a disallowed IP).

    By aggregating all these logs, you can create a comprehensive picture of the cluster’s network security posture at any time. Remember to also monitor Azure Activity Logs (for changes to network infrastructure, like if someone altered a UDR or NSG – those would appear in activity logs). Additionally, use Azure Monitor Metrics where applicable. For example, monitor the CPU and memory of your Azure Firewall – a spike could indicate it’s processing a flood of traffic (maybe a DDoS or misconfiguration). Monitor the count of blocked vs allowed flows over time to detect anomalies. - Continuous Improvement via Azure Security Center: Use Azure Security Center (Defender for Cloud) as a dashboard for your AKS segmentation posture. It will list issues like “AKS cluster not configured with authorized IPs” or “No NSG on subnet” or “Container registry not private” as security recommendations. This can be your guide for plugging any gaps you missed. It also provides a secure score – a high score indicates you’ve followed best practices like the ones in this guide. In highly regulated setups, consider running regular compliance scans or even hiring a third-party audit to verify the segmentation (e.g., network penetration tests focused on lateral movement). - Incident Response Integration: Finally, ensure that all these tools feed into an incident response plan. For instance, if Defender for Containers raises an alert that a pod is making port scans (which bypass your policies), be ready to quarantine that node/pod (you could cordon the node and investigate, or scale it down). If Azure Policy flags a violation, ensure the dev team is notified and the issue is corrected. Effective segmentation is not “set and forget” – it requires ongoing management and quick response to any issues that arise.

By using Azure’s native tools, you offload much of the heavy lifting of security monitoring and enforcement. Defender for Containers acts as an ever-vigilant guard inside the cluster (watching Kubernetes logs and node telemetry) , Azure Policy acts as the gatekeeper to prevent bad configs (and to audit the state) , and your diagnostic logs + Monitor give you the evidence and alerts needed to manage the system day-to-day. This complements the network segmentation architecture: even if a hole appears, you’ll quickly know and be able to fix it.

Footnotes & References: This guide builds upon Azure’s reference architectures for AKS and adheres to Azure’s well-architected framework for security. Key references include Microsoft’s AKS baseline architecture documentation , the AKS PCI-DSS compliance guidance , and Azure’s best practices for network isolation and Zero Trust networking . Azure’s official documentation for Defender for Cloud and Policy was used to summarize features . These footnotes point to specific sections for deeper reading on each topic. Implementing the above in your environment will greatly harden your AKS cluster by segmenting it at every layer and watching everything that flows through those segments.