In the world of Kubernetes on Azure, there’s been a longstanding default: any pod in your AKS cluster can query the Azure Instance Metadata Service (IMDS). That’s powerful — but also risky. Today, Microsoft introduces a preview feature that lets you block pod access to IMDS, tightening your cluster’s security boundaries.

Why Restrict IMDS?

IMDS is a REST API that provides VM metadata: VM specs, networking, upcoming maintenance events, and (critically) identity tokens. Because it’s accessible by default (via IP 169.254.169.254), a pod that’s compromised or misbehaving could exploit this to pull sensitive information or impersonate the node’s identity. That’s a serious threat.

By limiting which pods can reach IMDS, you reduce the “blast radius” of potential vulnerabilities.

How the Restriction Works (Preview)

• Non host network pods (hostNetwork: false) lose access to IMDS entirely once restriction is enabled.
• Host network pods (hostNetwork: true) retain access (they share the same network space as the node).
• Azure implements this via iptables rules on the node to block traffic from non-host pods.
• Tampering with iptables (e.g. via SSH or privileged containers) can break enforcement, so best practices like disabling SSH or avoiding privileged pods come into play.

Limitations & Considerations

Because this is still in preview, there are a number of tradeoffs:

• Many AKS add-ons do not support IMDS restriction (e.g. Azure Monitor, Application Gateway Ingress, Flux/GitOps, Azure Policy, etc.).
• Windows node pools aren’t supported yet.
• Enabling restriction on a cluster that uses unsupported add-ons will fail.
• After enabling or disabling, you must reimage the nodes (e.g. via az aks upgrade --node-image-only) to apply or remove the iptables rules.
• The feature is opt-in and isn’t backed by an SLA or warranty.

Getting Started: Enabling IMDS Restriction

1. Use Azure CLI 2.61.0+ and install or update aks-preview.
2. Register the IMDSRestrictionPreview feature and refresh the ContainerService provider.
3. Ensure OIDC issuer is enabled on your cluster (required).
4. To create a new cluster with this feature:az aks create ... --enable-imds-restriction
5. To enable it on an existing cluster:az aks update ... --enable-imds-restriction Then reimage nodes for enforcement.
6. To verify, deploy test pods with and without hostNetwork: true and attempt to curl IMDS — the non-host pods should fail, the host pods should succeed.
7. To disable, run az aks update --disable-imds-restriction and reimage.

Final Thoughts

This new capability gives AKS users an additional layer of defense: limiting which pods can access VM metadata and identities.

Reference: https://learn.microsoft.com/en-us/azure/aks/imds-restriction

Maxime.