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Using a CDN for common libraries may help, but doesn't always, and is something you should measure rather than just assume. The situation where a CDN actually h

Using a CDN for common libraries may help, but doesn't always, and is something you should measure rather than just assume. The situation where a CDN actually hurts performance is one I've seen periodically at different clients. When people talk about serving jQuery, or J. Random JavaScript library, from a CDN it means the specific version of jQuery (or whatever) that they're using. There's literally no guarantee that the specific version you need will be in any given user's browser cache, and this is exacerbated if you loading multiple libraries from a CDN, or from different CDNs. If your CDNs serve files with low latency then it may not be a big problem, but not all CDNs do. Slow responding CDNs will slow your page loads down, not the reverse. Moreover, if you're serving over HTTP2/SPDY there's even less likely to be a benefit to using a CDN. Again, it's something you need to measure. One area where a CDN (e.g., Cloudflare) can benefit you is by serving all your static content to offer users a low-latency experience regardless of where they are in the world, but that's rather a different matter from serving half a dozen libraries from half a dozen different CDNs.

richmarr 10y ago
> ... something you should measure rather than just assume How do people do this? My obstacle with this point is each CDN would have a different impact in each locale due to the locations of their points of presence, and CDN-ing each resource would a different impact based on the sites that particuar individual had visited. Measuring it in any useful way in advance of a change would be really hard unless I'm missing a trick, and measuring it in hindsight would require the kind of performance logging that PaaS-level apps don't have access to.
- leeoniya 10y ago
  my recommendation is to first serve everything yourself over TLS (minified, bundled, gzipped). if you can, run HTTP2. then measure. if this does not deliver the perf you expect (chances are that it will), then look into CDNs. if you need to serve media that needs a lot of bandwidth (expensive) then look into CDNs. if you need some form of real-time comm like WebSockets or WebRTC that actually requires low latency, look into distributed systems (amazon, google, azure, cloudflare?, etc..)
  - richmarr 10y ago
    Sure, my question was how people measure.
    - leeoniya 10y ago
      your best bet is https://developer.mozilla.org/en-US/docs/Web/API/Performance https://developer.mozilla.org/en-US/docs/Web/API/Performance combined with either IP2location or Geolocation apis.
- tombrossman 10y ago
  This would be extremely useful data to have and when I last looked I found little to go on. For example, how great would it be to have an extra column on a page like this with cache hit rates? https://cdnjs.com/libraries https://cdnjs.com/libraries Nice to have these free hosted assets, but I suspect that a lot of these are an additional download and not actually cached by the majority of visitors. Just having a rough estimate would be helpful when choosing whether to directly serve an asset or use a CDN.
- Eridrus 10y ago
  You can use JavaScript timers to measure how long things take to load and infer how many of the resources come from cache, etc.

richmarr 10y ago

> ... something you should measure rather than just assume How do people do this? My obstacle with this point is each CDN would have a different impact in each locale due to the locations of their points of presence, and CDN-ing each resource would a different impact based on the sites that particuar individual had visited. Measuring it in any useful way in advance of a change would be really hard unless I'm missing a trick, and measuring it in hindsight would require the kind of performance logging that PaaS-level apps don't have access to.

leeoniya 10y ago
my recommendation is to first serve everything yourself over TLS (minified, bundled, gzipped). if you can, run HTTP2. then measure. if this does not deliver the perf you expect (chances are that it will), then look into CDNs. if you need to serve media that needs a lot of bandwidth (expensive) then look into CDNs. if you need some form of real-time comm like WebSockets or WebRTC that actually requires low latency, look into distributed systems (amazon, google, azure, cloudflare?, etc..)
- richmarr 10y ago
  Sure, my question was how people measure.
  - leeoniya 10y ago
    your best bet is https://developer.mozilla.org/en-US/docs/Web/API/Performance https://developer.mozilla.org/en-US/docs/Web/API/Performance combined with either IP2location or Geolocation apis.
tombrossman 10y ago
This would be extremely useful data to have and when I last looked I found little to go on. For example, how great would it be to have an extra column on a page like this with cache hit rates? https://cdnjs.com/libraries https://cdnjs.com/libraries Nice to have these free hosted assets, but I suspect that a lot of these are an additional download and not actually cached by the majority of visitors. Just having a rough estimate would be helpful when choosing whether to directly serve an asset or use a CDN.
Eridrus 10y ago
You can use JavaScript timers to measure how long things take to load and infer how many of the resources come from cache, etc.