https://gomakethings.com/cdn-caching-isnt-the-performance-boost-it-used-to-be/
Just read this and was a bit surprised.
CDN's Aren't as Useful Anymore?
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Re: CDN's Aren't as Useful Anymore?
#2I used to link to other assets that were served from a CDN, but have now opted for things like system fonts, instead of bulky webfonts served from a CDN and heavily optimize any images that I serve (greyscale GIF FTW) aswell as GZIP'ing everything.
Re: CDN's Aren't as Useful Anymore?
#3tl;dr: There used to be a performance advantage when multiple sites loaded common resources from the same place, since it would often already be cached. But cross-domain caching could be used to violate your privacy, so browsers don't do it anymore, which nullifies that advantage.
Re: CDN's Aren't as Useful Anymore?
#4I thought CDNs were used mostly to reduce load on the server?
Re: CDN's Aren't as Useful Anymore?
#5CDNs are still useful if you (can/do) put everything on the same one. They’re just not useful to serve static dependencies off-site in hopes of users hitting a primed cache from another site, because of cache partitioning. That’s okay, that benefit was fairly limited anyway. You’re better off focusing on reducing page weight and optimizing loading (order, inlining critical resources, tree-shaking/code splitting, preloading to avoid waterfall, etc) anyway.
Re: CDN's Aren't as Useful Anymore?
#6To be clear: CDNs are still highly useful. This is just about using them to host third-party libraries rather than serving them yourself.
It's worth noting that even a decade ago, using a CDN for third-party libraries often failed to produce the envisioned benefits. I tested this a far number of times and the cost of doing multiple additional DNS lookups, negotiating HTTPS, etc. was often higher than expected and the proliferation of versions meant that while it's true that the average browser hitting your site had a copy of jQuery in the cache it wasn't likely to be the same version from the same CDN.
Since HTTP/2 went mainstream half a decade ago, that's become an even harder competition to win since the browser can efficiently request a large number of files simultaneously without any of that setup overhead.
There's also a security concern: unless you use Sub-Resource Integrity (SRI) you're giving the CDN owner full control of your site and the users' data. That's not a catastrophic risk but it's probably more than a potential minor performance benefit is worth.
The last reason not to use them is increasingly the most important: if you include something large like many sites do, you probably have a ton of code which is going to have to be downloaded but isn't actually used by your site. A custom bundle (with tree-shaking, etc.) is going to save a substantial amount of transfer and it's usually the case that transferring less will overwhelm all other concerns.
Re: CDN's Aren't as Useful Anymore?
#7"Just read this and was a bit surprised."
I was surprised by something similar. We are in us-east-1 and standing up in us-east-2 as a backup. Now we're starting to stand up in us-west-2. So naturally, I asked why do us-east-2 if we need to do us-west-2 anyways for regulatory compliance? Latency. Ok... why not use CloudFront, Lambda@edge, etc? There's still unacceptable latency. I dropped it there, but really wanted to ask how that's possible and what the target latency is. Oh well, someone smarter than me must have already looked at it - back to the grind.
Re: CDN's Aren't as Useful Anymore?
#8My knowledge of CDNs is limited but I assume that Moore's law will make CDNs obsolete because you will be able to efficiently and cheaply host your own data but then again webmasters will want to outsource it so they don't have to manage and maintain it.
Re: CDN's Aren't as Useful Anymore?
#9My knowledge of CDNs is limited but I assume that Moore's law will make CDNs obsolete because you will be able to efficiently and cheaply host your own data but then again webmasters will want to outsource it so they don't have to manage and maintain it.
Not to be rude, but you never understood how CDNs we're helpful, then, because they were about round trips and latency, which Moore's law does not help with. The point of cdms was to reduce the number of distinct resource objects that your browser requested, and that will continue to be good advice in many situations.
Re: CDN's Aren't as Useful Anymore?
#10To be clear: CDNs are still highly useful. This is just about using them to host third-party libraries rather than serving them yourself. It's worth noting that even a decade ago, using a CDN for third-party libraries often failed to produce the envisioned benefits. I tested this a far number of times and the cost of doing multiple additional DNS lookups, negotiating HTTPS, etc. was often higher than expected and the…
> It's worth noting that even a decade ago, using a CDN for third-party libraries often failed to produce the envisioned benefits.
This always seemed like a lot of hopeful mythology. As you said, there were so many versions, and then if you start combining the modules, and the various public CDNs, it becomes a combinatorics problem that you can only when if the browser cache is enormous. But even a pretty large browser cache becomes pretty small when auto-play video is a thing and 2mb seems small for a landing page.
CDNs are certainly useful, if you can serve your content from closer to the user, that reduces latency which also increases potential bandwidth early in a connection. It's often helpful to serve content through a CDN, even if it's not cached, as reducing the latency makes a big difference (and the edge origin connections can often be longer lived so that latency has less of an effect on the bandwidth available)