Normally, when one application needs to reach a service in a different network — a different VPC, a different AWS account, or an AWS service like S3 — that traffic has choices: travel across the public internet, or travel through more complex networking setups like VPC peering or a VPN, both of which can expose broader network ranges than actually necessary and add real configuration overhead.

AWS PrivateLink is a networking technology that lets you privately connect your VPC to supported AWS services, services hosted by other AWS accounts, or third-party SaaS providers — all without that traffic ever crossing the public internet, and without needing to peer entire networks together. From the consuming application’s point of view, the remote service simply appears as a private IP address inside its own VPC.

On the consuming side, a VPC creates an interface endpoint — a set of Elastic Network Interfaces (ENIs) with private IP addresses placed directly inside your subnets. Applications connect to these private IPs as if the remote service were local. On the providing side, a service is published as an endpoint service, typically backed by a Network Load Balancer that fronts the actual service instances.

flowchart LR
    A[Consumer VPC] --> B[Interface Endpoint - Private ENIs]
    B -->|AWS PrivateLink Network| C[Endpoint Service]
    C --> D[Network Load Balancer]
    D --> E[Service Instance 1]
    D --> F[Service Instance 2]
    D --> G[Service Instance 3]
        

Notice that the consumer’s traffic never needs a route to the public internet, an internet gateway, or a NAT device to reach the service. The private ENI sitting inside the consumer’s own subnet is the entire connection point.

When you create an interface endpoint, AWS provisions an ENI with a private IP address in each subnet you select, typically one per Availability Zone for resilience. Internally, PrivateLink traffic travels over Amazon’s own private network backbone, never touching the public internet’s routing infrastructure, which is precisely why it avoids the security exposure and variable latency that public internet paths can introduce.

When Private DNS is enabled for an endpoint, AWS automatically resolves the service’s normal domain name to the private ENI’s IP address whenever that resolution happens from inside the VPC — meaning existing application code that already calls the service by its regular hostname often needs no code changes at all to start using PrivateLink.

This lifecycle also applies symmetrically for both AWS-managed services (like accessing S3 or Kinesis privately from within a VPC) and third-party SaaS offerings that choose to publish their services through an endpoint service — the underlying mechanics are the same in both cases.

The trade-off is tight scope and strong isolation versus setup effort and per-endpoint cost. PrivateLink deliberately connects one specific service at a time rather than entire networks, which is safer but means each service relationship needs its own endpoint.

Because PrivateLink traffic runs over AWS’s own private backbone rather than the public internet, latency tends to be low and consistent, avoiding the variability that public internet routes can introduce during congestion. Interface endpoints scale automatically to handle increasing connection volume, and placing an ENI in each Availability Zone you use helps spread load and avoid cross-AZ data transfer where possible.

On the provider side, since traffic passes through a Network Load Balancer, the same NLB scaling characteristics apply — it distributes connections across many targets and scales to handle large volumes of concurrent traffic without manual intervention.

Interface endpoints support placing an ENI in multiple Availability Zones, meaning the loss of one AZ does not sever the private connection — traffic can continue flowing through the ENI in a remaining healthy zone. On the provider side, the underlying Network Load Balancer performs continuous health checks against backend targets, automatically routing traffic away from unhealthy instances.

Because PrivateLink connections rely on standard, well-understood AWS networking primitives — ENIs, Network Load Balancers, and VPC routing — the same reliability practices that apply broadly across AWS networking, like spreading resources across Availability Zones, apply directly here as well.

PrivateLink’s core security advantage is architectural: by design, traffic never touches the public internet, eliminating an entire category of exposure. On top of that, security groups attached to the interface endpoint’s ENIs control which resources within the consumer VPC can reach it at all.

Amazon CloudWatch exposes metrics for interface endpoints, including bytes processed and active connection counts, and for the underlying Network Load Balancer on the provider side, including target health and connection counts. VPC Flow Logs can also capture traffic flowing to and from the endpoint’s ENIs for deeper network-level visibility.

Because PrivateLink is a networking layer rather than an application layer, most meaningful troubleshooting metrics come from the surrounding components — ENIs, security groups, and load balancers — rather than from PrivateLink having a large monitoring surface of its own.

PrivateLink is used in two main deployment shapes. Interface endpoints connect your VPC privately to supported AWS services (like Amazon S3, Kinesis, or Secrets Manager) or to third-party services, appearing as a private IP in your own subnets. Endpoint services let you become the provider, publishing your own service to be consumed privately by other AWS accounts or customers.

Worth noting: Gateway endpoints are a related but distinct mechanism, used specifically for S3 and DynamoDB, implemented through VPC route tables rather than ENIs, and carrying no hourly endpoint charge — a useful, cheaper alternative for those two specific services when interface-endpoint features are not required.

A widely used pattern is SaaS provider connectivity: a SaaS company publishes an endpoint service, and its enterprise customers connect to it privately from within their own VPCs, avoiding public internet exposure for potentially sensitive data flowing to that SaaS platform. Another pattern is centralized shared services, where a hub VPC publishes internal tools (like a shared logging or secrets service) as endpoint services, consumed privately by many spoke VPCs across an organization.