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CDN vs web servers. Fundamental differences

My understanding is that a CDN is effectively comprised of HTTP servers that are closer to the client. Their primary goal is to deliver cached content (e.g. multimedia) at low latency. Is that understanding correct? Or is that analogy misguided?

If so, is it safe to state that CDNs would typically:

  • not accept PUT / POST / DELETE requests that intend to modify data?
  • not establish connections to a DB across the network to deliver or manipulate data in general

Or am I wrong on the above and on how they are intended to be used in practice?

Solution

  • CDN is used to keep static files, for example HTML, JavaScript, CSS, images:

    A content delivery network is a geographically distributed group of servers optimized to deliver static content to end users. This static content can be almost any sort of data, but CDNs are most commonly used to deliver web pages and their related files, streaming video and audio, and large software packages.

    See also Using a CDN to Speed Up Static Content Delivery

    So of course it can't contain API, access to DB or any server side logic.