CDN is a network of geographically dispersed servers used to deliver static content. CDN servers cache static content like images, videos, CSS, JS files, etc.

Dynamic Content Cache: It enables the caching of HTML pages based on request path, query strings, cookies, and request headers.

How it works:

When a user visits a website, a CDN server closest will deliver static content.

Considerations of using CDN

1. Cost: Since third parties run it, it will cost you.
2. Setting upon appropriate cache expiry, not too long, not too short.
3. CDN fallback: If CDN fails/outrages, the client side should be able to detect the problem and request resources from the origin.

Invalidating files

You can remove a file from CDN before it expires by following operations:

1. By using API provided by the vendor
2. By using object versioning to serve a different version of the object, we can add parameters to the URL, such as version number.
3. Web servers no longer serve static assets (JS, CSS, images, etc.). They are fetched from the CDN for better performances.
4. The caching data lightens database load.

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