Unlocking Private IP for Azure Application Gateway: Security, Compliance, and Practical Deployment
If you’re responsible for securing, scaling, and optimizing cloud infrastructure, this update is for you. Based on my recent conversation with Vyshnavi Namani, Product Manager on the Azure Networking team, I’ll break down what private IP means for your environment, why it matters, and how to get started. Why Private IP for Application Gateway? Application Gateway has long been the go-to Layer 7 load balancer for web traffic in Azure. It manages, routes, and secures requests to your backend resources, offering SSL offloading and integrated Web Application Firewall (WAF) capabilities. But until now, public IPs were the norm, meaning exposure to the internet and the need for extra security layers. With Private IP, your Application Gateway can be deployed entirely within your virtual network (VNet), isolated from public internet access. This is a huge win for organizations with strict security, compliance, or policy requirements. Now, your traffic stays internal, protected by Azure’s security layers, and only accessible to authorized entities within your ecosystem. Key Benefits for ITPRO 🔒 No Public Exposure With a private-only Application Gateway, no public IP is assigned. The gateway is accessible only via internal networks, eliminating any direct exposure to the public internet. This removes a major attack vector by keeping traffic entirely within your trusted network boundaries. 📌 Granular Network Control Private IP mode grants full control over network policies. Strict NSG rules can be applied (no special exceptions needed for Azure management traffic) and custom route tables can be used (including a 0.0.0.0/0 route to force outbound traffic through on-premises or appliance-based security checkpoints). ☑️ Compliance Alignment Internal-only gateways help meet enterprise compliance and data governance requirements. Sensitive applications remain isolated within private networks, aiding data residency and preventing unintended data exfiltration. Organizations with “no internet exposure” policies can now include Application Gateway without exception. Architectural Considerations and Deployment Prerequisites To deploy Azure Application Gateway with Private IP, you should plan for the following: SKU & Feature Enablement: Use the v2 SKU (Standard_v2 or WAF_v2). The Private IP feature is GA but may require opt-in via the EnableApplicationGatewayNetworkIsolation flag in Azure Portal, CLI, or PowerShell. Dedicated Subnet: Deploy the gateway in a dedicated subnet (no other resources allowed). Recommended size: /24 for v2. This enables clean NSG and route table configurations. NSG Configuration: Inbound: Allow AzureLoadBalancer for health probes and internal client IPs on required ports. Outbound: Allow only necessary internal destinations; apply a DenyAll rule to block internet egress. User-Defined Routes (UDRs): Optional but recommended for forced tunneling. Set 0.0.0.0/0 to route traffic through an NVA, Azure Firewall, or ExpressRoute gateway. Client Connectivity: Ensure internal clients (VMs, App Services, on-prem users via VPN/ExpressRoute) can reach the gateway’s private IP. Use Private DNS or custom DNS zones for name resolution. Outbound Dependencies: For services like Key Vault or telemetry, use Private Link or NAT Gateway if internet access is required. Plan NSG and UDRs accordingly. Management Access: Admins must be on the VNet or connected network to test or manage the gateway. Azure handles control-plane traffic internally via a management NIC. Migration Notes: Existing gateways may require redeployment to switch to private-only mode. Feature registration must be active before provisioning. Practical Scenarios Here are several practical scenarios where deploying Azure Application Gateway with Private IP is especially beneficial: 🔐 Internal-Only Web Applications Organizations hosting intranet portals, HR systems, or internal dashboards can use Private IP to ensure these apps are only accessible from within the corporate network—via VPN, ExpressRoute, or peered VNets. 🏥 Regulated Industries (Healthcare, Finance, Government) Workloads that handle sensitive data (e.g., patient records, financial transactions) often require strict network isolation. Private IP ensures traffic never touches the public internet, supporting compliance with HIPAA, PCI-DSS, or government data residency mandates. 🧪 Dev/Test Environments Development teams can deploy isolated environments for testing without exposing them externally. This reduces risk and avoids accidental data leaks during early-stage development. 🌐 Hybrid Network Architectures In hybrid setups where on-prem systems interact with Azure-hosted services, Private IP gateways can route traffic securely through ExpressRoute or VPN, maintaining internal-only access and enabling centralized inspection via NVAs. 🛡️ Zero Trust Architectures Private IP supports zero trust principles by enforcing least-privilege access, denying internet egress, and requiring explicit NSG rules for all traffic—ideal for organizations implementing segmented, policy-driven networks. Resources https://docs.microsoft.com/azure/application-gateway/ https://learn.microsoft.com/azure/application-gateway/configuration-overview https://learn.microsoft.com/azure/virtual-network/network-security-groups-overview https://learn.microsoft.com/azure/virtual-network/virtual-network-peering-overview Next Steps Evaluate Your Workloads: Identify apps and services that require internal-only access. Plan Migration: Map out your VNets, subnets, and NSGs for a smooth transition. Enable Private IP Feature: Register and deploy in your Azure subscription. Test Security: Validate that only intended traffic flows through your gateway. Final Thoughts Private IP for Azure Application Gateway is an improvement for secure, compliant, and efficient cloud networking. If you’re an ITPRO managing infrastructure, now’s the time check out this feature and level up your Azure architecture. Have questions or want to share your experience? Drop a comment below. Cheers! PierreApplication Gateway WAF custom rule is not triggered if the HTTP header field is not present
Hi Community, I have this strange behavior on my Application Gateway WAF. I created this custom rule (see image below) to deny traffic when the http request has Referer http header field empty or missing. The problem is that this rule is only triggered when the Referer http header field is empty but not when it is missing 😞 Instead, the same custom rule is working fine on the front door WAF. Why is it happening? Did I do something wrong?
