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129 lines
5.7 KiB
Markdown
129 lines
5.7 KiB
Markdown
# CloudFront
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## What is it?
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[[_CloudFront|CloudFront]] is a CDN. It can be used for:
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- Static & Dynamic content
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- Video Streaming
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- Web Sockets
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### Benefits
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- [[_CloudFront|CloudFront]] can be fronted with [[AWS WAF]] for OWASP's top 10 protection.
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- [[_CloudFront|CloudFront]] can stream [[Videos On Demand]] using [[ISS Microsoft Smooth Streaming]]
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### Core components
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**Origin**: Location where all original files are located. Examples include: S3, EC2, ELB, Route53.
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**Edge Locations**: Compute located strategically close to end users.
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**Regional Caches**: Compute located in board geographical locations to speed up requests for edge locations.
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**Distribution**: A collection of Edge locations and Regional Cache that defines how cached content should behave.
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## Running Code
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### Stages where [[Lambda@Edge]] and [[CloudFront Functions]] can trigger
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The order that the functions trigger within CloudFront is:
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| Order | Stage | L@E | CF Fns | Description | Example Use Cases |
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|--|---|---|---|---|--|
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| 1 | Viewer Request | ✔️ | ✔️ | When CloudFront receives a request from the viewer. | Redirection (`HTTP` -> `HTTPS`), Cookie Inspection for Auth, Modify Headers for A/B Testing |
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| 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 |
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| 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). |
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| 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. |
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```mermaid
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sequenceDiagram
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participant Viewer
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participant Edge
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participant Origin
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Viewer->>Edge: Viewer Request
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Edge->>Origin: Origin Request
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Origin->>Edge: Origin Response
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Edge->>Viewer: Viewer Response
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```
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### Difference between [[Lambda@Edge]] and [[CloudFront Functions]]
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| | CF Fns | L@E |
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|---|---|---|
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| Programming Languages | JavaScript (ECMAScript 5.1) | Node.JS and Python |
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| Event Sources | Viewer only | Viewer and Origin |
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| Scale | +10,000,000 requests/s | 10,000 requests/s/Region |
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| Function Duration | Submilisecond | Up to 5s (Viewer) / Up to 30s (Origin) |
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| Max Memory | 2MB | 128MB-3,008MB |
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| Max Bundle Size | 10KB | 1MB (Viewer) / 50MB (Origin) |
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| Network, File System, and Request Body Access | ❌ | ✔️ |
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| Access to geolocation | ✔️ | ❌ (Viewer request) / ✔️ (Origin request & response, Viewer response) |
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| Can build/test entirely within CloudFront | ✔️ | ❌ |
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| Functions logging and metrics | ✔️ | ✔️ |
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| Pricing | Cheaper. Free tier available; charged pre request. | More expensive. Charged per request & function duration. |
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## CloudFront Origin
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It's the source where CloudFront will send requests.
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### CloudFront Origin Groups
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It allows you to group a **primary** and **secondary origin** together as a destination for requests to enable high availability and fault tolerance.
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The **Primary Origin** is where **all** the requests will be sent.
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The **Secondary Origin** is where the requests will be sent if the **Primary Origin** is **not available**. It will act like a **failover** origin.
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The **failover** criteria is based on **HTTP Status Codes**: 400, 403, 404, 416, 500, 502, 503, 504.
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CloudFront will failover on: `GET`, `HEAD`, and `OPTION` requests.
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CloudFront will NOT failover on: `PUT`, `POST`, `PATCH`, and `DELETE`.
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## CloudFront Caching Policy
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### Cache Key
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The **Cache Key** is a unique identifier for every object in the cache and determines whether a viewer request results in a cache hit.
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A cache hit occurs when a viewer request generates the same **Cache Key** as a prior request and the object for that cache key is in the edge location's cache.
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The more people hit the cache, the better the application performance will be.
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### Cache Policy
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A **Cache Policy** determines the **Cache Key**.
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AWS has managed **Cache Policies** for use:
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- `Amplify`
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- `CachingDisabled`
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- `CachingOptimized`
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- `CachingOptimizedForUncompressedObjects`
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- `Elemental-MediaPackage`
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You can make your own **Caching Policy**:
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- **TTL Settings**:
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- **Minimum** / **Maximum** **TTL**: min / max time to hold the file in the cache.
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- **Default TTL**: default time to hold a file in the cache.
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- **Cache Key Settings**:
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- **Headers**: which headers are a part of the **Cache Key**.
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- **Cookies**: which cookies are a part of the **Cache Key**.
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- **Query String**: which query string parameters are a part of the **Cache Key**.
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- **Compression Support**: What compression format is part of the **Cache Key**.
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### Origin Request
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Happens when there is a cache miss and CloudFront must reach out to Origin to retrieve data.
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**Origin Request** always returns:
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- URL Path
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- Request Body (if present)
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- Specific HTTP Headers:
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- Host
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- User Agent
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- `X-Amz-Cf-Id`
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**Origin Request** doesn't include these by default:
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- URL Query String
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- Cookies
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- All other HTTP Headers
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**Cache Key** information (set by the **Cache Policy**) are automatically included in **Origin Requests**:
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- URL Query Strings
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- HTTP Headers
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- Cookies
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### Response Header Policy
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Allows you to modify the HTTP Headers in the response that viewers will see.
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AWS has managed policies for you to use and you can make your own also.
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⚠️ If you are dealing with CORS, you will be setting things here, as this will mess with them.
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## Origin Access Identity
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**OAI** makes sure that an S3 bucket is only accessible through **CloudFront** and not the internet.
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Lots of drawbacks.
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