Private Link

Private Link makes the outside feel like the inside.

Services that live in someone else's data center appear to live in yours. You access cloud storage, databases, and SaaS applications through private IP addresses in your own network. Traffic never touches the public Internet. From your application's perspective, these services are just... there, on the local network, as if they'd been there all along.

The Problem: Public Services, Private Networks

Here's the traditional dilemma: Your applications run in private subnets with no Internet access—that's the whole point of private subnets. But cloud services like object storage and databases have public endpoints. To reach them, you need Internet gateways, NAT devices, public IP addresses, firewall rules allowing outbound traffic.

Suddenly your "private" network has a path to the entire Internet.

Every outbound connection is a potential attack vector. Every public endpoint is a shared address that anyone can reach. Your traffic crosses the public Internet alongside everyone else's, protected only by encryption.

Private Link eliminates this contradiction. Instead of your private network reaching out to public services, the services reach in.

How It Works

Private Link creates a network interface in your subnet—an actual elastic network interface with a private IP address from your range. This interface is an endpoint, a portal to a service that exists elsewhere.

When your application connects to that private IP, the cloud provider's network handles the rest. Traffic flows through their internal backbone, never crossing the public Internet, never needing public addressing. The service could be three data centers away, but to your application it looks like a local resource.

This is the clever fiction: your network believes the service is inside. The service's network knows it's receiving private traffic. Everyone agrees to maintain this illusion, and the illusion works.

What Each Cloud Provider Calls It

The concept is identical across providers. The naming differs.

AWS PrivateLink uses "interface endpoints" (network interfaces with private IPs) and "gateway endpoints" (route table entries for S3 and DynamoDB only, no data processing charges).

Azure Private Link uses "private endpoints" with private IPs from your subnet. Network Security Groups control access.

Google Cloud Private Service Connect uses "endpoints" with VPC IP addresses and Service Directory for DNS.

Same pattern: create an endpoint in your network, point it at a service, access that service privately.

DNS: The Missing Piece

Here's where it gets subtle. If your application calls storage.googleapis.com or s3.amazonaws.com, that DNS name still resolves to a public IP by default. Your private endpoint sits there unused.

Private Link requires DNS to lie—in a helpful way. Service names must resolve to your private endpoint IPs instead of public addresses. AWS creates private hosted zones automatically. Azure and GCP require explicit DNS configuration.

Get this wrong and your traffic still flows over the Internet, defeating the entire purpose.

Beyond Cloud Services: Third-Party SaaS

Private Link isn't just for first-party cloud services. Datadog, Snowflake, MongoDB Atlas, and dozens of other SaaS providers publish endpoints you can consume.

The pattern: they create a service on their side. You create an endpoint on yours. Now you have private connectivity to a third-party service using the same mechanism as native cloud services. Your security posture improves without the SaaS provider changing anything about how they operate.

Publishing Your Own Services

The reverse also works. You can publish your own services through Private Link for other accounts or organizations to consume privately.

This enables a clean architecture for shared services within large organizations or for SaaS providers offering private connectivity to customers. Your service gets an endpoint in their network. Their traffic reaches you without crossing the public Internet. No VPN tunnels, no peering agreements, no firewall rule negotiations.

What It Costs

Private endpoints have hourly charges. Traffic through them incurs data processing fees (varies by provider). DNS zones add their own costs.

But you're potentially eliminating NAT gateways and their data processing charges. You're simplifying firewall rules. You're removing Internet gateways from private subnet architectures.

Do the math for your specific traffic patterns. High-volume access to cloud services often makes Private Link cost-effective even before considering the security benefits.

When Private Link Matters

Compliance requirements prohibiting Internet exposure. Zero-trust architectures requiring private connectivity for all service access. High-bandwidth workloads where Internet routing introduces latency variability. Any situation where "traffic stays private" is a hard requirement rather than a preference.

Private Link isn't about blocking the Internet. It's about making the Internet unnecessary for accessing services that used to require it.