Troubleshooting Azure Private Link

This guide provides common troubleshooting steps and solutions for issues you might encounter when using Azure Private Link. Private Link enables you to securely access Azure PaaS services and Azure-hosted customer-owned services over a private endpoint from your Azure virtual network.

Common Issues and Resolutions

1. Cannot Connect to the Private Endpoint

If you are unable to establish a connection to your service via the private endpoint, consider the following:

Network Security Groups (NSGs): Ensure that NSGs applied to the subnet containing your private endpoint allow outbound traffic to the service. For example, if connecting to Azure SQL Database, ensure port 1433 is allowed.
Firewall Rules: Check any firewalls in your environment (Azure Firewall, Network Virtual Appliances) for rules that might be blocking traffic.
Route Tables: Verify that there are no route table entries that incorrectly direct traffic away from the private endpoint.
Private DNS Zone Configuration: Ensure that the Private DNS Zone is correctly configured and linked to your virtual network. The A record should resolve to the private IP address of the private endpoint.
Service Health: Check the Azure Service Health dashboard for any ongoing incidents that might affect the target service.

2. Private Endpoint IP Address Not Accessible

When the private endpoint's IP address is not reachable from your virtual network:

VNet Peering/VPN/ExpressRoute: If connecting from a peered VNet, VPN gateway, or ExpressRoute circuit, verify that the routing is correctly configured and that the private IP address range of the private endpoint is reachable.
Subnet Delegation: Ensure that the subnet where the private endpoint is deployed is not delegated to another service.
Network Policies: If you have network policies (e.g., Azure Policy, NSGs) applied at the subnet level, ensure they are not inadvertently blocking traffic.

3. DNS Resolution Issues

Problems with DNS resolution are frequent causes of Private Link connectivity issues:

Private DNS Zone Status: Confirm that the Private DNS Zone for the target service is created, correctly named (e.g., privatelink.blob.core.windows.net for Azure Storage), and linked to the virtual network(s) from which you are accessing the service.
DNS Records: Verify that the A record for your service endpoint (e.g., yourstorageaccount.blob.core.windows.net) is correctly registered in the Private DNS Zone and points to the private IP address of your private endpoint.
Custom DNS Servers: If you are using custom DNS servers, ensure they are configured to forward queries for the relevant Private DNS Zones to Azure DNS or that they can resolve the records directly.
Client-side DNS: Check the DNS configuration on the client machines within your virtual network.

Tip: DNS Verification

Use tools like nslookup or dig from within your virtual network to test DNS resolution for your service endpoint. For example: nslookup yourstorageaccount.blob.core.windows.net. The output should show the private IP address of the private endpoint.

4. Service-Specific Configuration

Some Azure services have specific configuration requirements for Private Link:

Azure Storage: Ensure that the storage account's public network access is disabled or restricted to selected virtual networks, and that the private endpoint is correctly associated with the storage account.
Azure SQL Database: Verify that the SQL server firewall rules do not block access from the private endpoint's VNet.
Azure Key Vault: Confirm that Key Vault network access is configured to allow access from the private endpoint.

Advanced Troubleshooting

Using Network Watcher

Azure Network Watcher provides several tools to help diagnose network connectivity issues:

IP Flow Verify: Checks if traffic is allowed or denied by NSG rules.
Connection Troubleshoot: Tests connectivity between two endpoints.
Packet Capture: Captures network traffic to analyze communication patterns.
Connection Monitor: Monitors network reachability and performance between endpoints.

Traffic Analytics

Enable Traffic Analytics for your Network Security Groups and Azure Firewall to gain insights into network traffic flows, identify potential bottlenecks, and troubleshoot connectivity issues.

Azure Monitor and Logs

Leverage Azure Monitor to collect and analyze logs from your private endpoint, target service, and network infrastructure. This can help identify errors or unexpected behavior.

Important: Resource Provider Registration

Ensure that the necessary resource providers are registered for the services you are using with Private Link (e.g., Microsoft.Network, Microsoft.Storage, Microsoft.Sql).

Troubleshooting Checklist

Verify Private Endpoint Status in Azure Portal.
Check Network Security Groups (NSGs) for allowed traffic.
Review Azure Firewall or NVA rules.
Confirm Route Table configurations.
Validate Private DNS Zone creation, linking, and record accuracy.
Test DNS resolution from the client VNet.
Check service-specific firewall and network access settings.
Use Network Watcher tools for in-depth diagnostics.
Monitor Azure Monitor logs for relevant events.

Warning: Deleting Private Endpoints

Deleting a private endpoint will revoke access to the service. Redeployment will be necessary if access is required again.