Comparing Azure Private Links and Service Endpoints

Introduction

Azure offers various services to enhance the security and connectivity of its cloud resources. Two such services, Azure Private Links and Service Endpoints, have provided secure access to multi-tenant, Platform-as-a-Service (PaaS) resources. This blog aims to elucidate these services' evolution, functionalities, and how they compare.

The Evolution of Azure Connectivity

Initially, accessing multi-tenant PaaS versions of many Azure services meant connecting over the internet without the ability to restrict access exclusively to your resources. This limitation was due to the complexities of restricting access in a multi-tenant environment. Solutions either opted for single-tenant services like App Service Environment or self-hosted services in VMs.

Microsoft responded to this security concern by introducing Service Endpoints and Private Link/Endpoints, restricting who can connect to your service and how.

Overview of Service Endpoints

Service Endpoints were the first solution to lock down multi-tenant service access. They allow you to restrict access to our PaaS resources to traffic from our Azure Virtual Network. While Service Endpoints limit the PaaS service to identify and allow traffic from our VNet, the traffic still exits our VNet to access the PaaS service. However, it's configured to recognize traffic from our VNet, facilitating direct routing and optimal traffic flow without exposing public IPs.

Key Features of Service Endpoints:

• Supported by a wide range of Azure services.
• Traffic is routed optimally to Azure resources.
• The PaaS resource sees traffic coming from our VNet's private IP.
• No requirement for IP filtering or NAT translation.

Limitations of Service Endpoints:

• Traffic still leaves our VNet and the PaaS resource is accessed via its public address.
• Cannot be used by on-premises traffic without whitelisting public IPs.

Overview of Private Link

Azure Private Link is a more recent and advanced solution. Unlike Service Endpoints, Private Link injects the multi-tenant PaaS resource directly into our VNet, assigning it a private IP within our VNet. All traffic to the PaaS resource is contained within the virtual network, enhancing security and reducing exposure.

Key Features of Private Link:

• Traffic to PaaS resources does not leave the virtual network.
• Supports access from on-premises networks via VPN or ExpressRoute.
• Allows connections to resources across regions and Azure AD tenants.
• Each endpoint is linked to a specific PaaS instance, preventing data leakage.

Limitations of Private Link:

• Requires DNS configuration changes, potentially complicating integration with existing DNS services.
• Might incur additional costs based on the number of endpoints and traffic.

Detailed Comparison

Connectivity

• Service Endpoint: Traffic leaves the VNet but is secured to the Azure backbone network. This means while traffic is more secure than the public internet, it still exits your VNet to reach the PaaS service.
• Private Endpoints: Provide direct, secure connectivity within the VNet. The traffic to the PaaS resources does not leave your virtual network, significantly enhancing security and reducing exposure.

Data Security

• Service Endpoint: While the traffic is secured to the Azure backbone, there's still a risk as the data travels outside the VNet. Additionally, the PaaS resource is accessed via its public address, which could be a potential security concern.
• Private Endpoints: Offer enhanced data security as no data leaves the virtual network. This reduces the risk of data exfiltration significantly. Each endpoint is linked to a specific instance of the PaaS resource, providing fine-grained access control and preventing unauthorized data access.

On-premises Connectivity

• Service Endpoint: Limited support. It does not natively support traffic originating from on-premises over VPN or ExpressRoute. For on-premises access, public IPs must be whitelisted, which can be a security concern.
• Private Endpoints: Offer full support for on-premises connectivity through VPN or ExpressRoute. This feature allows seamless and secure connections from your on-premises network to Azure services without exposing your data to the public internet.

Complexity

• Service Endpoint: Generally easier and quicker to set up with less complexity. It's suitable for scenarios where the additional security of Private Links is not required, or where the setup simplicity is a priority.
• Private Endpoints: More complex to implement, requiring careful network planning and DNS configuration changes. This complexity is justified by the higher security and direct connectivity it offers, making it suitable for environments with stringent security requirements.

Cost

• Service Endpoint: Usually, there are no additional costs for using Service Endpoints, making it a cost-effective option for securing access to Azure services.
• Private Endpoints: The cost is based on the number of endpoints, inbound and outbound data processed. While it offers superior features and security, it might lead to higher costs depending on the usage pattern and scale of deployment.

Cross-region Support

• Service Endpoint: Generally, it does not support cross-region connections natively. This can be a limitation for organizations operating in multiple regions.
• Private Endpoints: Provide full support for cross-region connectivity, allowing resources in different regions to communicate securely. This is beneficial for multi-regional deployments and ensuring consistent access controls across the board.