Choosing Between Gateway Endpoint or Interface Endpoint For S3 | Overview.

Intro:

•        Which is most suitable: Gateway Endpoint or Interface Endpoint for S3.
•        Choosing Between Gateway Endpoint or Interface Endpoint Types for S3, is a core AWS networking decision that affects cost, scalability, and performance.
•         twtech Overview of when and why Gateway Endpoint or Interface Endpoint for S3 is more suited, especially for Amazon S3 access from within a VPC.

Breakdown:

•         Analysis of Gateway  Endpoint & Interface Endpoint for S3,
•         Gateway  Endpoint or Interface Endpoint Types in Context,
•         Choosing Between Gateway Endpoint or Interface Endpoint Types for S3,
•         Real-World Scenarios,
•         Architecture (Summary Diagram),
•         Final thoughts.

Analysis of Gateway  Endpoint & Interface Endpoint for S3

Endpoint Type	Best For	S3 Suitability
Gateway Endpoint	Accessing S3 or DynamoDB via private routes (within same region)	✅ Most suitable for S3
Interface Endpoint (PrivateLink)	Accessing AWS services over private IPs through ENIs (supports most other services)	⚠️ Possible but not recommended for S3 due to higher cost & complexity

Gateway  Endpoint & Interface Endpoint Types in Context.

1. Gateway Endpoint

•         Mechanism: Adds a special route in your route table directing S3 or DynamoDB traffic to the service over the AWS backbone (not the internet).
•         No ENIs or IPs are created — it’s a control-plane construct.
•         Highly scalable and cost-effective.

How It Works (S3 case)

When an EC2 instance in a private subnet tries to access an S3 bucket:

•         The VPC route table sends traffic destined for s3.amazonaws.com to the Gateway Endpoint.
•         Traffic stays within the AWS network (no NAT, no public IP, no Internet Gateway).
•         Data flows privately and securely.

Advantages

•         Free: No hourly charge; twtech only pay for S3 data transfer and requests.
•         Highly scalable: No ENIs, no bandwidth limits.
•         Simple setup: Just add to route tables.
•         No IP management: Nothing to configure in subnets or security groups.
•         Supports S3 bucket policies that restrict access only via the VPC endpoint (tightens security).

 Limitations

•         Only supports S3 and DynamoDB.
•         Doesn’t work cross-region.
•         Not visible as an ENI (no private IP-based access).

2. Interface Endpoint (AWS PrivateLink)

•         Mechanism: Creates one or more Elastic Network Interfaces (ENIs) in twtech subnet with private IP addresses that connect to the AWS service endpoint.
•         These ENIs act as private entry points for the service.

How It Works (S3 case)

•        twtech can technically create an S3 Interface Endpoint (via PrivateLink).
•        However:
•         It uses PrivateLink through ENIs.
•         Traffic goes through the VPC’s ENI IPs, not via routing.
•         Each ENI adds a per-hour and per-GB data processing charge.

 Disadvantages for S3

•         Cost: twtech pays per endpoint + per GB of data processed.
•         Performance: Not as scalable as Gateway; PrivateLink adds an extra hop.
•         Complexity: Requires Security Group configuration and IP management.
•         Intended Use Case: For services without Gateway endpoints, not for S3.

 Choosing Between Gateway Endpoint or Interface Endpoint Types for S3

Criteria	Gateway Endpoint	Interface Endpoint
Cost	Free (no hourly/data processing fee)	$$$ per-hour + per-GB charge
Performance	Scales automatically	Bandwidth limited by ENI
Security Groups	Not needed	Required
Ease of Setup	Simple (route table entry)	More complex (ENI + SG rules)
Traffic Path	Routed within AWS backbone	PrivateLink via ENI
Typical Use	S3, DynamoDB	SSM, Secrets Manager, ECR API, CloudWatch, etc.
Recommended for S3?	✅ Yes	❌ No (only use if twtech must use PrivateLink)

 Real-World Scenarios

Scenario	Recommended Endpoint
Accessing S3 buckets from private subnets without Internet/NAT Gateway	✅ Gateway Endpoint
Need to access non-S3 services (e.g., SSM, Secrets Manager) privately	Interface Endpoint
S3 service in GovCloud or isolated regions	Gateway Endpoint
Multi-account architecture needing centralized access (PrivateLink)	Possibly Interface, but S3 Gateway with bucket policy is usually better

 Architecture (Summary Diagram)

twtech Final thoughts

•        For S3 access from a VPC, the Gateway Endpoint is the best choice — cost-efficient, scalable, and purpose-built for S3.
•        Use Interface Endpoints (PrivateLink) for services that don’t support Gateway endpoints, such as SSM, Secrets Manager, ECR, CloudWatch, etc.