Here are some popular CDN providers that will work with CDN for Joomla!
- Amazon CloudFront
- Azure CDN (Microsoft)
- StackPath (previously MaxCDN)
- ... and more ...
CDN for Joomla! is made to work with any CDN system that supports Pull Zones.
A Pull Zone works in a way that you do not have to upload any media. The Pull Zone uploads the media to the CDN servers as soon as it is required.
A Pull Zone is what is needed to utilize the HTTP Caching type of CDN. The name Pull Zone came from the technique used, as the CDN service "pulls" the static assets from your website to cache it and serve it from the CDN network.
CDN for Joomla! does NOT upload files to your CDN server. As said, CDN for Joomla! only works with CDN systems that pull (upload) the media to the server on request.