3 ms·

It's normal for most smaller CDNs to not have their PoPs communicate, yes. With larger CDNs you start to get hierarchical caches: https://trafficserver.readthe

by buro9 11y ago

It's normal for most smaller CDNs to not have their PoPs communicate, yes. With larger CDNs you start to get hierarchical caches: https://trafficserver.readthedocs.org/en/5.3.x/admin/hierachical-caching.en.html https://trafficserver.readthedocs.org/en/5.3.x/admin/hierach... The theory being that the PoP closest to the origin is the one responsible for going to the origin and thus that other PoPs will fetch cached items for the closest PoP to origin. Nearly all of the very large CDNs support some degree of hierarchical caching, and the ones becoming large are gaining the capability. At CloudFlare (where I work) the need for a hierarchical cache was low priority until we started to rapidly increase our global capacity... once you reach a certain scale then the need for some way to have PoPs not visit the origin more than once for an item becomes very important. You can be sure we're working on that (if you are an Enterprise customer you could contact sales to enquire about beta testing for it). But right now, for us and many other providers, just enabling an nginx cache in front of any expensive resource will help. By "expensive", I generally mean anything that will trigger extra expenditure or processing when it could be cached. Edit: Additionally, nearly every CDN is operating an LRU cache. You haven't bought storage and not everything you've ever stored is being held in cache. You only need a few bots (GoogleBot, Yandex, Baidu, etc) constantly spidering to be pulling the long tail of files from your backend S3 if you haven't got your own cache in front of it. Hierarchical caching isn't a silver bullet that takes care of all potential costs incurred, but having your own cache is.

aembleton 11y ago
What size is the Cloudflare cache on the Free and Pro plans?
- buro9 11y ago
  It's a question without an exact answer. It depends where your origin is, where your users are (near 1 PoP? 2 PoPs? spread evenly globally?), how frequently files that can be cached are requested, the capacity of each PoP, the contention of each PoP, etc. A few years ago when the customer and traffic growth rate exceeded the network expansion rate the answer was probably "not big enough", but we've since upgraded almost every PoP and added a huge number of new ones: https://www.cloudflare.com/network-map/ https://www.cloudflare.com/network-map/ The answer now is "more than big enough". We cache as much as possible, for as long as possible. The more requested a file, the more likely it is to be in the cache even if you're on the Free plan. Lots of logic is applied to this, more than could fit in this reply. But importantly; there's no difference in how much you can cache between the plans. Wherever it is possible, we make the Free plan have as much capability as the other plans.
rakoo 11y ago
Thanks for the detailed answer. The only technical understanding of a CDN I have is from CoralCDN (http://www.coralcdn.org/ http://www.coralcdn.org/), a p2p CDN operated by researchers on PlanetLab (with servers all around the world) that was especially created to mitigate flash crowds scenario, and their very documentation on this experiment (http://www.coralcdn.org/pubs/ http://www.coralcdn.org/pubs/, particularly http://www.coralcdn.org/docs/coral-nsdi04.pdf http://www.coralcdn.org/docs/coral-nsdi04.pdf). I was impressed by how the nodes automagically coordinate themselves so that as few as possible will query upstream, and then content will be slowly propagated to other nodes that were requesting for this exact content in a form of multicast tree, all with 0 administration and thanks to a smart DHT and a smart DNS implementation. Really cool stuff. I was under the impression that any commercial CDN was doing at least the same.

by buro9 11y ago

aembleton 11y ago

What size is the Cloudflare cache on the Free and Pro plans?

buro9 11y ago
It's a question without an exact answer. It depends where your origin is, where your users are (near 1 PoP? 2 PoPs? spread evenly globally?), how frequently files that can be cached are requested, the capacity of each PoP, the contention of each PoP, etc. A few years ago when the customer and traffic growth rate exceeded the network expansion rate the answer was probably "not big enough", but we've since upgraded almost every PoP and added a huge number of new ones: https://www.cloudflare.com/network-map/ https://www.cloudflare.com/network-map/ The answer now is "more than big enough". We cache as much as possible, for as long as possible. The more requested a file, the more likely it is to be in the cache even if you're on the Free plan. Lots of logic is applied to this, more than could fit in this reply. But importantly; there's no difference in how much you can cache between the plans. Wherever it is possible, we make the Free plan have as much capability as the other plans.

rakoo 11y ago

Thanks for the detailed answer. The only technical understanding of a CDN I have is from CoralCDN (http://www.coralcdn.org/ http://www.coralcdn.org/), a p2p CDN operated by researchers on PlanetLab (with servers all around the world) that was especially created to mitigate flash crowds scenario, and their very documentation on this experiment (http://www.coralcdn.org/pubs/ http://www.coralcdn.org/pubs/, particularly http://www.coralcdn.org/docs/coral-nsdi04.pdf http://www.coralcdn.org/docs/coral-nsdi04.pdf). I was impressed by how the nodes automagically coordinate themselves so that as few as possible will query upstream, and then content will be slowly propagated to other nodes that were requesting for this exact content in a form of multicast tree, all with 0 administration and thanks to a smart DHT and a smart DNS implementation. Really cool stuff. I was under the impression that any commercial CDN was doing at least the same.