The top google results from amazon and Cloudflare say it all. Here and here.

As far as my concerns go, I am interested in the web application layer, maybe the db layer.

It’s about performance and cost.

A really good video from roadmap.sh about Web Cache and HTTP Caching Headers here. Server level/Application level caching, for example redis or memcached. Or client side. Reduces latency, cuts down the bandwidth, reduced load on the server.

Three locations: browser cache, proxy server cache, reverse proxy server cache.

Caching headers: expires, pragma, content-control

The preferred caching header is the Cache-Control header

Validator headers: etag, if-none-match, last-modified, if-modified-since