Using AWS SAM to Create Secure Private APIs
Learn how to build secure, private APIs using AWS SAM with best practices for enterprise-grade security.
Why Private APIs Matter in Serverless Architecture
In today’s security-conscious environment, private APIs have become essential for enterprise applications. Unlike public APIs that are accessible from the internet, private APIs are only accessible within your Virtual Private Cloud (VPC) or through VPC endpoints. This significantly reduces the attack surface and helps meet compliance requirements.
AWS SAM (Serverless Application Model) simplifies the process of creating and managing private APIs. With just a few lines of configuration, you can deploy a secure API that’s only accessible within your AWS environment.
How AWS SAM Simplifies Private API Creation
AWS SAM is an open-source framework that extends AWS CloudFormation to provide simplified syntax for defining serverless applications. It reduces the boilerplate code needed to define API Gateway resources, Lambda functions, and security configurations.
Define Your API in SAM Template
Specify your API Gateway as private using the EndpointConfiguration property:
Resources:
MyApi:
Type: AWS::Serverless::Api
Properties:
StageName: Prod
EndpointConfiguration: PRIVATE
Auth:
DefaultAuthorizer: AWS_IAMConfigure Resource-Based Policies
Control which VPCs or AWS accounts can access your private API:
Policies:
- Version: '2012-10-17'
Statement:
- Effect: Allow
Principal: '*'
Action: execute-api:Invoke
Resource: execute-api:/*
Condition:
StringEquals:
aws:SourceVpc: vpc-12345678Deploy with SAM CLI
Use the SAM command line interface to package and deploy your application:
sam build sam deploy --guided
Security Best Practices for Private APIs
While private APIs are more secure by design, you should implement additional security measures:
| Security Measure | Implementation | Benefit |
|---|---|---|
| Resource Policies | Restrict access to specific VPCs or accounts | Prevents unauthorized network access |
| IAM Authorization | Require IAM credentials for API access | Ensures only authenticated users can invoke |
| VPC Endpoints | Use Interface VPC Endpoints (PrivateLink) | Keeps traffic within AWS network |
| WAF Integration | Add AWS WAF to your API Gateway | Protects against common web exploits |
| Logging & Monitoring | Enable CloudTrail and CloudWatch | Provides audit trail and detection |
Real-World Security Scenario
A financial institution processes sensitive customer data through their internal systems. By using a private API with IAM authorization and VPC endpoints, they ensure that:
- API traffic never leaves the AWS network
- Only authorized internal systems can access the API
- All requests are logged for compliance auditing
Troubleshooting Common Issues
When working with private APIs, developers often encounter these challenges:
Connectivity Problems
Symptom: API calls from your VPC are timing out.
Solution: Ensure that:
- Your VPC has a route to the VPC endpoint
- The security group allows outbound HTTPS (port 443) traffic
- The resource policy allows traffic from your VPC ID
Permission Errors
Symptom: Receiving “403 Forbidden” errors even from within VPC.
Solution: Verify that:
- The calling IAM role has
execute-api:Invokepermission - The resource policy doesn’t have conflicting deny rules
- You’re using the correct API endpoint (private vs public)
{api-id}-{vpce-id}.execute-api.{region}.amazonaws.comAdvanced Implementation Patterns
Hybrid Architecture with On-Premises Access
To allow on-premises systems to access your private API:
- Establish AWS Direct Connect or VPN connection
- Create a VPC endpoint for API Gateway
- Update route tables to direct API traffic through the endpoint
- Add your corporate IP range to the resource policy
Cross-Account Private API Access
Enable secure API access across AWS accounts:
Policies:
- Version: '2012-10-17'
Statement:
- Effect: Allow
Principal:
AWS: arn:aws:iam::123456789012:root
Action: execute-api:Invoke
Resource: execute-api:/*Conclusion: Building Secure Serverless APIs
Implementing private APIs with AWS SAM provides a robust security foundation for your serverless applications. By following the patterns and best practices outlined in this guide, you can:
- Reduce your application’s attack surface
- Meet strict compliance requirements
- Simplify network security architecture
- Maintain high performance with VPC endpoints
As you implement these solutions, remember to:
- Always start with the principle of least privilege
- Regularly review your resource policies
- Monitor API usage patterns for anomalies
- Combine private APIs with other security layers
Additional Resources
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