On 2020/03/19 00:55, tom ryan wrote: > On 2020-03-18 19:42, Stuart Henderson wrote: > > On 2020-03-17, Flipchan <flipc...@riseup.net> wrote: > >> Yeah the point with a cdn is to lower the latency of it so therefor you > >> what is needed is just not only a fast http server but a traffic > >> redirector depending on the end users origin > > > > Doing this via redirects does not lower latency, it increases it. > > > > It may reduce overall time to fetch objects if they are large enough > > that faster transfers speed things up enough to offset the higher > > latency from connecting to one server, requesting, being redirected, > > connecting to the second server, requesting, receiving content. > > This is equally true if there are many objects to fetch, especially if > they aren't all fetched at once - they don't need to be large for the > magic to help.
It's faster than a cold connection, but "request from A, wait for reply, see that it's a redirect, request from B, wait for reply" is always going be higher latency before starting to receive the requested object directly from B. > > To reduce latency you need another way to direct users to a nearby > > server without doing redirects. Usually either geolocation-aware DNS > > that hands out an IP address close to the user's DNS resolver (this > > can have problems if the user uses a non-local resolver as is the case > > with some DNS privacy services, but is not usually too bad - look at > > thd geoip flavour of the isc-bind port, or gdnsd)), or BGP anycast with > > connections to other networks around the world (as well as BGP skills, > > you need an AS number, at least a /24 of address space that you can use > > for this purpose, and hosting providers that will allow you to make BGP > > announcements). > > I've never used this, but it definitely attempts to solve these issues: > https://trafficcontrol.apache.org/ > > IIRC it was developed at Comcast for VOD (ie many large objects), and is > built around Apache Traffic Server (ex Yahoo) > > It uses DNS to get as close as it can, then 302s the first HTTP request > based on source IP > > Alternatively the pages pulling in the content can do a dynamic > > lookup and use a local-to-the-user hostname when referencing > > the objects (<script src="//www-eu.example.org/resource.js"> etc.. > > What kind of in-browser dynamic lookup do you mean here? Something based > on language, or maybe localtime? I meant server-side when generating the page, doing a lookup from either route tables or a geolocation database and picking a suitable hostname. > > This might also be of interest to the OP: > https://developers.google.com/speed/pagespeed/module/ > On-the-wire > > t > > > Or of course you can outsource it (limelight, vdms, fastly, > > cloudflare, cachefly, edgecast, cloudfront, akamai and others). > > >
