Lambda@Edge and CloudFront Functions

Here's a comprehensive comparison between Lambda@Edge and CloudFront Functions:

1. Runtime Environment:

• Lambda@Edge: Node.js and Python

• CloudFront Functions: JavaScript only (ECMAScript 5.1)

1. Execution Context:

• Lambda@Edge: Can run at four stages:

  • Viewer Request

  • Origin Request

  • Origin Response

  • Viewer Response

• CloudFront Functions: Only two stages:

  • Viewer Request

  • Viewer Response

1. Performance & Scale:

• Lambda@Edge:

  • Startup latency: ~1-2ms

  • Maximum runtime: 5-30 seconds

  • Memory: 128MB to 10GB

• CloudFront Functions:

  • Startup latency: sub-millisecond

  • Maximum runtime: < 1ms

  • Memory: 2MB

1. Use Cases: Lambda@Edge:

• Complex processing

• Third-party API calls

• Large-scale manipulations

• Access to AWS services

• Cookie manipulation

• Complex redirects

• Authentication/Authorization

CloudFront Functions:

• URL rewrites/redirects

• Header manipulation

• Simple A/B testing

• Request normalization

• Simple authentication

• Cache key normalization

• Request validation

1. Pricing:

• Lambda@Edge: Pay for compute time and requests

• CloudFront Functions: Significantly cheaper, pay per request only

1. Development & Deployment: Lambda@Edge:

exports.handler = async (event) => {
    const request = event.Records[0].cf.request;
    const headers = request.headers;
    
    // Complex processing here
    const response = await fetch('https://api.example.com/data');
    
    return request;
};

CloudFront Functions:

function handler(event) {
    var request = event.request;
    var headers = request.headers;
    
    // Simple header manipulation
    headers['x-custom-header'] = {value: 'some-value'};
    
    return request;
}

1. Key Limitations: Lambda@Edge:

• Regional deployment required

• Longer cold starts

• Higher latency for complex operations

CloudFront Functions:

• No external network calls

• Limited runtime

• No filesystem access

• No access to additional AWS services

Choose CloudFront Functions when:

• You need simple, lightweight processing

• Sub-millisecond performance is crucial

• Cost optimization is important

• Processing is limited to viewer request/response

Choose Lambda@Edge when:

• You need complex processing

• External API calls are required

• You need access to AWS services

• Processing at origin request/response is needed