URL Fingerprinting / Agressive Caching with NGINX + Express

Fingerprinting and Etags are separate features for reducing load times.

Etags avoid having to resend an asset if the browser has cached it and the asset has not changed. But, a separate HTTP roundtrip is still required for the browser to send an If-None-Match and get back 304 Not Modified.

The best way of speeding up an HTTP roundtrip is to avoid making one at all. When the second page of a website uses the same assets as the first page, and those assets have far future cache expires headers, then there is no need to even make a single round trip for those assets when they are requested after the first time.

Fingerprinting is the technique of giving each asset a unique name that is derived from its content. Then, when even one bit in an asset (such as a CSS bundle) changes, its name changes, and so a browser will GET the updated asset. And, because fingerprinting uses a cryptographic hash of the contents, the unique name is calculated the same across multiple servers, as long as the asset is identical. Caches everywhere (CDNs, at ISPs, in networking equipment, or in web browsers) are able to keep a copy of each asset, but since the HTML references the unique name of each asset, only the correct version of that asset will ever be served from a cache.

Both Etags and fingerprinting are supported by every browser.

1. Fingerprinting is not required, it is an optimization. If you are using technologies like Stylus, Browserify, and AngularTemplateCaches that already require a build step, than adding fingerprints is cost-free.

2. Your HTML pages will have names like /aboutus instead of the /aboutus-sfghjs3646dhs73shwsbby3 they would get with fingerprinting. All the solutions you link to support fingerprinting of Javascript, CSS, and images, and a way to dynamically substitute in the fingerprinted name to the HTML. So, the HTML will reference /css-hs6hd73ydhs7d7shsh7w until you change a byte in the CSS, and then they will reference /css-37r7dhsh373hd73 (a different file).

3. Fingerprints only need to be generated when the file is modified, which should generally be on server restart or build.

4. I recommend Asset Rack, which supports lots of asset types, and can serve the fingerprinted assets from RAM or push them to a CDN. It generates all fingerprints each time Express is started up.