What is Lambda@Edge?

Lambda@Edge is an AWS service that allows you to run Lambda functions at AWS Edge locations globally. It is designed to customize the behavior of CloudFront distributions, enabling low-latency execution of code closer to users.

Key Features of Lambda@Edge

1. Global Execution: Executes code at AWS edge locations near the user for low latency.
2. Event-Driven: Integrates with CloudFront events (viewer requests, origin requests, viewer responses, origin responses).
3. No Servers to Manage: Fully serverless; AWS manages scaling and infrastructure.
4. Supports Multiple Use Cases:
   • Header modification
   • Dynamic request/response customization
   • URL redirection and rewriting
   • Authentication and authorization
   • Data compression and caching optimization

Integration Points

Lambda@Edge integrates directly with CloudFront events:

• Viewer Request: Triggered when the client makes a request to CloudFront.
• Origin Request: Triggered before CloudFront forwards a request to the origin server.
• Origin Response: Triggered after receiving a response from the origin server.
• Viewer Response: Triggered just before CloudFront returns the response to the client.

Best Practices

1. Use Lightweight Functions:
   • Keep functions small and optimized for quick execution to reduce latency.
2. Avoid Long-Running Tasks:
   • Perform heavy computations or database queries outside Lambda@Edge.
3. Securely Handle Sensitive Data:
   • Ensure sensitive data is encrypted and managed securely.

Example Scenarios

1. Dynamic Content Localization:
   • Use the Viewer Request trigger to detect the user's country via headers and serve region-specific content.
2. Header-Based Caching:
   • Add or modify headers in Origin Request or Viewer Response to improve cacheability.