AWS Interface Endpoints Explained

How AWS PrivateLink Enables Private Connectivity to AWS Services

Interface Endpoints allow resources within your Virtual Private Cloud (VPC) to communicate privately with AWS services without requiring an Internet Gateway, NAT Gateway, or public IP address. These endpoints are powered by AWS PrivateLink, which creates a private connection between your VPC and supported AWS services.

How AWS Interface Endpoints Work

When you create an Interface Endpoint, AWS provisions an Elastic Network Interface (ENI) within one or more subnets in your VPC. This ENI receives a private IP address that acts as the entry point for traffic destined for the AWS service.

The traffic flow typically looks like this:

• Application inside a private subnet sends traffic to the service endpoint
• DNS resolves the AWS service hostname to the Interface Endpoint
• Traffic is routed through AWS PrivateLink
• The request reaches the AWS service securely without touching the public internet

AWS Interface Endpoint Architecture

Example architecture showing private connectivity between a VPC and AWS services using an Interface Endpoint.

Common AWS Services Using Interface Endpoints

Many AWS services support Interface Endpoints, allowing secure and private communication from your VPC:

• AWS Secrets Manager
• AWS Systems Manager
• Amazon CloudWatch
• AWS Key Management Service (KMS)
• Amazon Elastic Container Registry (ECR)
• AWS Security Token Service (STS)
• Amazon SNS

These endpoints are especially useful in environments where outbound internet access is restricted or tightly controlled.

Interface Endpoints vs Gateway Endpoints

Common Interface Endpoint Gotchas

• DNS Configuration: Private DNS must be enabled for the endpoint to override the public service hostname.
• Availability Zones: Endpoints should be deployed in each AZ where workloads run.
• Security Groups: Interface Endpoints are controlled by security groups, which can block traffic if misconfigured.
• Costs Add Up: Each endpoint incurs hourly charges plus data processing fees.
• Multiple Endpoints Required: Some services require multiple endpoints (example: ECR + S3).

Real-World Use Case

A common enterprise pattern is running applications in fully private subnets with no internet access. Instead of routing traffic through a NAT Gateway, organizations deploy Interface Endpoints for services such as Secrets Manager, CloudWatch, and Systems Manager.

This design significantly reduces attack surface while allowing applications to continue interacting with AWS APIs securely.

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