DVA-02-Notes/CloudFront/_CloudFront.md

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.

Lambda@Edge and CloudFront Functions

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