Azure Private Link Connectivity

This article describes the connectivity aspects of Azure Private Link, a service that enables you to access Azure Platform as a Service (PaaS) and customer-owned/partner services in Azure over a private endpoint from your Azure Virtual Network (VNet).

Key Connectivity Components

Azure Private Link establishes a secure and private connection between your virtual network and Azure services. The core components facilitating this connectivity are:

• Virtual Network (VNet): Your private network in Azure where your resources reside.
• Private Endpoint: A network interface that uses a private IP address from your VNet, effectively bringing the Azure service into your VNet.
• Private Link Service: A service you create in Azure to expose your own services (e.g., in a VNet) to consumers over Private Link.
• Azure Service: The PaaS service (e.g., Azure Storage, Azure SQL Database) or a customer/partner service you wish to connect to privately.

How Connectivity Works

When you create a private endpoint for an Azure service, the service is assigned a private IP address within your VNet. This means traffic to the service flows through your VNet and bypasses the public internet. The process generally involves:

1. Deployment: You deploy a private endpoint in your VNet, targeting a specific Azure service.
2. IP Assignment: Azure assigns a private IP address from your VNet's address space to the private endpoint's network interface.
3. DNS Resolution: For seamless connectivity, you typically configure Azure Private DNS Zones. This ensures that when your applications try to resolve the public FQDN (Fully Qualified Domain Name) of the service, they are directed to the private IP address of the private endpoint.
4. Traffic Flow: All traffic destined for the service from your VNet is routed directly to the private endpoint's private IP address, maintaining privacy and security.

Conceptual diagram illustrating Azure Private Link connectivity.

Connectivity Scenarios

1. Connecting to Azure PaaS Services

This is the most common use case. You can connect to services like:

• Azure Storage (Blob, Files, Queues, Tables)
• Azure SQL Database
• Azure Cosmos DB
• Azure Key Vault
• And many more...

By using a private endpoint, your applications within your VNet can access these services without traversing the public internet, enhancing security and reducing latency.

2. Connecting to Your Own Services (Self-Hosted)

You can also expose your own applications running on Azure VMs or other compute services using Private Link Service. This allows consumers (other VNets, on-premises networks via VPN/ExpressRoute) to connect to your service privately.

3. Connecting from On-Premises

To connect from your on-premises network to an Azure service via Private Link, you need a hybrid connectivity solution:

• VPN Gateway or ExpressRoute: Establish a connection between your on-premises network and your Azure VNet.
• VNet Peering: If the private endpoint is in a different VNet, ensure VNet peering is configured correctly.
• DNS: Proper DNS resolution for the private IP address from on-premises is crucial.

DNS Configuration for Private Endpoints

Correct DNS resolution is vital for Private Link to function seamlessly. When a private endpoint is created, it's associated with a specific Azure Private DNS Zone (e.g., privatelink.blob.core.windows.net for Azure Blob Storage).

The private endpoint receives a private IP address. You need to ensure that when your applications try to resolve the FQDN of the service (e.g., yourstorageaccount.blob.core.windows.net), they get back the private IP address of the private endpoint. This is typically achieved by:

• Linking the Azure Private DNS Zone to your VNet.
• Creating an 'A' record in the DNS Zone that maps the service's FQDN to the private IP address of the private endpoint.

For example, an 'A' record might look like:

Name: yourstorageaccount.blob.core.windows.net
Type: A
IP Address: 10.0.0.4 (example private IP)
            

Network Security Groups (NSGs)

Network Security Groups applied to the subnet where the private endpoint resides will affect traffic flow. You need to ensure that NSG rules allow traffic to and from the private endpoint's IP address. For most Azure PaaS services, the traffic is already secured once it enters the Azure backbone.

By leveraging Azure Private Link, you can significantly enhance the security posture of your cloud applications by eliminating public internet exposure for sensitive data and services.