cdn on Alperen Doc

cloudfront-cdn

Mon, 01 Jan 0001 00:00:00 +0000

CloudFront CDN#

How does Netflix serve a 14 GB 4K video file to a user on demand? Two options include:

They can compress the video data as much as possible (compression).
They can chunk the video into smaller pieces and send it piece by piece (chunking/streaming).

But neither of those solves the problem of initial load time (how long until the first frame starts after hitting “play”). To get fast initial loads, we also need a quick round-trip time (RTT). If you’re a gamer, it’s basically the same as server ping: the time it takes for a request to go from your computer to the server and back.

cloudfront-distributions

Mon, 01 Jan 0001 00:00:00 +0000

CloudFront Distributions#

A CloudFront distribution is the configuration that tells CloudFront:

Where your content is (the origin, like your S3 bucket)
How to deliver it (caching behavior, compression, etc.)
Who can access it (security settings)

When you create a distribution, CloudFront assigns it a domain name, like d1234567890.cloudfront.net, which you can use to access your content through the CDN.

Key Configuration Options#

Origin: The source of your content (S3 bucket, EC2 instance, load balancer, etc.)
Default root object: What file to serve for the root URL (e.g. index.html)
Distribution settings: Caching behavior, compression, HTTPS, etc.
Price class: Which edge locations to use (affects cost and coverage)

CDNs are typically used to serve static content, like images, videos, and documents. You may have heard of Lambda@Edge for actual computational request/response logic close to users… more on that later.

cloudfront-invalidation

Mon, 01 Jan 0001 00:00:00 +0000

CloudFront Invalidation#

A CDN is a geographically distributed cache, which means it’s one of the hardest things to deal with…

“There are 2 hard problems in computer science: cache invalidation, naming things, and off-by-1 errors.”

– Leon Bambrick

If you update the favicon in your S3 bucket, it won’t immediately update for users accessing it through CloudFront.

Similarly, if you use CloudFront to serve content like HTML, CSS, or JavaScript files for a website, users might not see the latest version of your site immediately after you make changes.

presigned-urls

Mon, 01 Jan 0001 00:00:00 +0000

Presigned URLs#

Serving files is nice, but we often want CDN speed while still limiting access to specific users. To do that, we can use presigned URLs.

Presigned URLs are temporary, time-limited URLs that grant access to private S3 objects or CloudFront content. They’re like tickets that expire:

Time-limited: The URL expires after a set duration (e.g., 1 hour, or 24 hours).
Secure: The content itself remains private; only those with the presigned URL can access it.
Controlled: You control who gets the URL and when it expires.

Here’s what a presigned URL looks like:

why-use-presigned-urls

Mon, 01 Jan 0001 00:00:00 +0000

Why Use Presigned URLs?#

You just learned how to create presigned URLs, but you might be wondering: why go through all this trouble? Well, imagine you’re building a course platform where students can download PDFs of their course materials. If you make the PDFs public in S3 then all the content would be accessible for free!

…and unless you’re as cool as Boot.dev, you probably don’t want that.

Anyone with the URL can access the files (even people who aren’t enrolled)
Search engines and bots can crawl and index your content
You have no control over who downloads what
Once someone has the URL, they can share it forever

This is where presigned URLs shine. Instead of making your S3 bucket or CloudFront content publicly accessible, you can use presigned URLs to get the best of both worlds: CDN speed with a private-content access control. You dish out presigned URLs to paying users, they download the content before the URL expires, and once it does, their URL becomes useless. By setting extremely short expiry times, and generating a new URL when a paying user requests it, they can effectively keep access forever, but will only be able to get the content if they’re going through your link generator.

cloudfront-with-dns

Mon, 01 Jan 0001 00:00:00 +0000

CloudFront With DNS#

Your CloudFront distribution has a domain name like d1234567890abcdef.cloudfront.net, but that’s a long, hard-to-remember address.

To make it easier for users to find your content, you can create your own DNS record that points a friendly domain name to your CloudFront distribution. Instead of typing that long CloudFront URL, users can type something like cdn.yourcoolsite.com.

If you’re using Route 53, you can use an ALIAS (A) record instead of a CNAME. ALIAS records work better at the zone apex and are free. They also are a bit more plug-and-play within AWS if you’re using CloudFront, but CNAME also works just fine.