CloudFront

What is it?

_CloudFront is a CDN. It can be used for:

Static & Dynamic content
Video Streaming
Web Sockets

Benefits

_CloudFront can be fronted with AWS WAF for OWASP's top 10 protection.
_CloudFront can stream Videos On Demand using ISS Microsoft Smooth Streaming

Core components

Origin: Location where all original files are located. Examples include: S3, EC2, ELB, Route53. Edge Locations: Compute located strategically close to end users. Regional Caches: Compute located in board geographical locations to speed up requests for edge locations. Distribution: A collection of Edge locations and Regional Cache that defines how cached content should behave.

Stages where Lambda@Edge and CloudFront Functions can trigger

The order that the functions trigger within CloudFront is:

Order	Stage	L@E	CF Fns	Description	Example Use Cases
1	Viewer Request	✔️	✔️	When CloudFront receives a request from the viewer.	Redirection (`HTTP` -> `HTTPS`), Cookie Inspection for Auth, Modify Headers for A/B Testing
2	Origin Request	✔️	❌	Before CloudFront forwards the request to the origin.	Add security headers (CSP/HSTS), set cookies for client side tracking, customise error messages
3	Origin Response	✔️	❌	After CloudFront receives the request from the origin.	Rewrite URLs for SEO or routing, inject headers for origin authentication, selective content serving based on user agent (desktop/mobile mode).
4	Viewer Response	✔️	✔️	Before CloudFront returns the response to the viewer.	Modify headers to control caching, update URLs in HTML for versioning, customise error responses from origin.

sequenceDiagram
    participant Viewer
    participant Edge
    participant Origin

    Viewer->>Edge: Viewer Request
    Edge->>Origin: Origin Request
    Origin->>Edge: Origin Response
    Edge->>Viewer: Viewer Response

Difference between Lambda@Edge and CloudFront Functions

	CF Fns	L@E
Programming Languages	JavaScript (ECMAScript 5.1)	Node.JS and Python
Event Sources	Viewer only	Viewer and Origin
Scale	+10,000,000 requests/s	10,000 requests/s/Region
Function Duration	Submilisecond	Up to 5s (Viewer) / Up to 30s (Origin)
Max Memory	2MB	128MB-3,008MB
Max Bundle Size	10KB	1MB (Viewer) / 50MB (Origin)
Network, File System, and Request Body Access	❌	✔️
Access to geolocation	✔️	❌ (Viewer request) / ✔️ (Origin request & response, Viewer response)
Can build/test entirely within CloudFront	✔️	❌
Functions logging and metrics	✔️	✔️
Pricing	Cheaper. Free tier available; charged pre request.	More expensive. Charged per request & function duration.

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