An AWS interface endpoint represents a horizontally scaled, redundant VPC endpoint that exposes supported AWS services and SaaS offerings privately to your resources within a virtual private cloud. Instead of traffic traversing the public internet, communication occurs over the private AWS network, which reduces latency, eliminates exposure to the public internet, and supports private connectivity using private IP addresses from your VPC.
How interface endpoints work under the hood
At the network level, an interface endpoint creates elastic network interfaces inside your chosen subnets, each assigned private IP addresses within the CIDR range of your VPC. These ENIs act as entry points for supported services such as Amazon S3, DynamoDB, Lambda, and many AWS managed services via PrivateLink. When a resource in your VPC sends traffic to the service’s private DNS name, the VPC resolver routes the request to the corresponding network interface, keeping the path entirely within the AWS global network backbone.
Security and access control mechanisms
You govern access to interface endpoints using standard VPC mechanisms such as security groups and network ACLs, allowing you to define fine-grained rules for allowed traffic at the instance and port level. Integration with AWS Identity and Access Management enables condition keys and policy-based controls that restrict which principals can create connections to the endpoint. For services powered by PrivateLink, you can also apply resource policies that specify which accounts or VPCs are permitted to interface with the endpoint, adding an additional layer of governance.
Interface endpoints versus gateway endpoints
Gateway endpoints target only Amazon S3 and DynamoDB, operate at the route table level, and are confined to these two services with no support for private IP-based policies. In contrast, interface endpoints are powered by Elastic Network Interfaces, support a broad catalog of AWS services and SaaS offerings, and allow the use of private DNS, security groups, and detailed monitoring. While gateway endpoints avoid NAT and data transfer charges within the same region, interface endpoints provide private connectivity to a wider range of targets, including linked VPCs and cross-account services.
Architectural patterns and high availability considerations
For high availability, provision interface endpoints in at least two private subnets across different Availability Zones. This design ensures that if one AZ experiences disruption, traffic can fail over to the ENI in the other AZ without breaking connectivity. Combine interface endpoints with VPC endpoints policies and AWS PrivateLink to expose services securely to on-premises networks through AWS Direct Connect or VPN, maintaining private connectivity regardless of the source location.
Cost structure and operational implications
You are charged for interface endpoints based on hourly endpoint availability and the amount of data processed through the endpoint, measured in gigabytes. Additional costs include elastic network interfaces, private IP address consumption, and cross-zone data transfer if endpoints and resources span multiple Availability Zones. Monitoring endpoint health via CloudWatch metrics and setting up alarms for connection failures helps prevent surprises in your monthly bill and supports efficient capacity planning.
Best practices for deployment and lifecycle management
Deploy interface endpoints using infrastructure as code tools such as AWS CloudFormation or the AWS Cloud Development Kit to ensure consistent configuration across environments. Enable private DNS only when you want automatic routing via the service’s native DNS name; otherwise, update your resource records to point to the interface endpoint’s network interface DNS name. Regularly review endpoint policies, rotate security group rules, and test failover between Availability Zones to validate redundancy and maintain a robust security posture.
