AWS | Using Interface Endpoint Vs Arn

Interface Endpoint is used to connect to services like SQS, SNS, Secret Manager, ECR CloudWatch, but these services can be accessed directly through their ARNs, then what is the benefit of Interface Endpoint? 

Key Clarification

ARN controls authorization
VPC Endpoint controls network routing

These are completely different layers.

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Without Interface Endpoint

Let’s say your EC2 instance calls SQS:

EC2 → sqs.us-east-1.amazonaws.com

Even if:

• You use the correct ARN
• IAM permissions are correct

The traffic still:

1. Leaves your VPC

2. Goes through:

• Internet Gateway OR
• NAT Gateway
3. Travels over public AWS endpoints

Even though it's inside AWS backbone, it's still using public endpoints.

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With Interface Endpoint

Now:

EC2 → Private ENI inside VPC → SQS

Traffic:

• Never goes to internet
• Never needs NAT Gateway
• Never needs public IP
• Stays fully private

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So What's the Real Benefit?

No Internet Required

If your subnet is fully private:

• No IGW
• No NAT
• No public IP

Your EC2 cannot reach service SQS/SNS/SSM etc. at all without:

• NAT Gateway + IGW OR
• Interface Endpoint (Without NAT and IGW)

So the Interface endpoint enables connectivity in fully private networks.

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Stronger Security Posture

Without endpoint:

• Your subnet must have outbound internet access.

With endpoint:

• You can remove NAT completely.
• Block all outbound internet traffic.
• Only allow traffic to specific AWS services.

Much tighter security boundary.

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Endpoint Policy Control (Very Powerful)

Interface endpoints support endpoint policies.

Example:

{
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": "*",
      "Action": "sqs:SendMessage",
      "Resource": "arn:aws:sqs:us-east-1:123456789012:my-queue"
    }
  ]
}

Now even if IAM allows more, the endpoint itself restricts what can pass through.

This gives network-level authorization filtering.

You cannot do this with just ARN + IAM alone.

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Compliance & Regulated Environments

In regulated industries (banking, healthcare):

Rules may require:

• No internet connectivity
• No public endpoints
• Private routing only

Interface endpoints satisfy those requirements.

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NAT Gateway Cost Optimization

NAT Gateway is expensive.

If you only need AWS service access (SQS, SSM, SNS, etc.):

You can:

• Remove NAT
• Use interface endpoints

For high-traffic systems, this can save serious money.

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When You DON’T Need Interface Endpoint

If:

• Your subnet already has NAT
• You are OK with outbound internet access
• No strict compliance requirements
• Low security sensitivity

Then you may not need it.

Small projects often skip it.

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Real Production Example

Private EKS cluster:

• No public subnets
• No NAT
• No outbound internet allowed

Pods need to:

• Pull images from ECR
• Read secrets
• Send SQS messages
• Register with SSM

Without interface endpoints?

❌ Not possible.

With interface endpoints?

✅ Fully private operation.

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Final Answer

You don't use interface endpoints for permission.

You use them for:

• Private networking
• Security isolation
• Compliance
• Removing internet dependency
• Reducing NAT usage