On Wed, 2021-03-17 at 10:43 -0400, Calum McConnell wrote: > there are many different places where it is stated that you should > select a local mirror rather than the CDN, and a large part of the > community still holds that belief.
Do you have some examples of these places or people? I expect that most of the docs were simply written before the CDN existed and that Debian hasn't fully communicated with the community about using the CDN rather than the mirrors. > Is that confirmed? Depends who you ask, certainly the DSA folks who set up use of the CDN, shut down the mirror redirector (httpredir), switched security.d.o and ftp.d.o to the CDN, made d-i default to the CDN and demoted the mirror choice question in d-i definitely prefer that folks use the CDN. Right now I personally think that on balance the CDN is the best option for many people. People in specific circumstances probably should instead use local mirrors or the mirrors on the Tor onion service. There is one downside common to both CDNs and mirrors: The debdeltas aren't on a CDN nor mirrored anywhere, so the bandwidth used for updating on bandwidth-constrained devices is potentially expensive international traffic instead of local traffic. There some downsides of CDNs though: There are parts of the world that our CDN provider (Fastly) isn't great in, doesn't have coverage in or could get banned in. There are networks where local traffic is gratis but external traffic costs money (such as cloud providers) or counts to quota and the CDN provider is unlikely to have nodes within all of these networks. CDN providers are an opportunity for MITM attacks, the design of the Debian repo format mitigates most of these attacks though. The same attacks of course apply to each mirror but are limited to its users. Each CDN node does not contain a full copy of the apt repository, so there are fewer full copies of Debian out there. The benefit provided by https is lower for the CDN than the mirror, since the range of file sizes being transferred is lower to the CDN domain (which is just Debian) than to mirrors (which have more files). There are some downsides of the mirror network too: Having to choose a specific mirror is not something many computer users want to be doing, so requiring a choice rather than just making one global worldwide mirror (aka CDN) the default means the audience for Debian is restricted to geeks, power users and folks who know them or can hire them. The hosting trend worldwide is towards CDNs rather than mirrors, so the amount of mirrors is likely to go down over time. The popularity of Debian derivatives means that Debian gets mirrored less and in some cases ISPs make the choice to drop Debian mirrors but keep the derivatives. Lots of mirrors are very suboptimal, they stop updating, or do updates in the wrong way leading to errors on user systems or just silently leave user systems without updates. We have no mirror redirector nor apt mirror:// provider. Consequently the user experience when a mirror is created or goes bad isn't great, as the submitter of this thread found, they need to be vigilant about finding new local mirrors, or need to manually update after errors. Since mirrors come and go, the copy of the mirror list within d-i will always be outdated to some extent. I'm not sure if d-i auto-updates the mirror list when it gets network though? The ftp.CC.debian.org country-specific mirror aliases have to be manually updated by the DSA folks rather than being automatically updated from the mirror monitoring service. The new mirror additions have to be manually added rather than being automatically added to the mirrors list after a successful monitoring period. The mirrors that die or stop being updated have to be manually removed from the mirrors list rather than automatically being removed. There is no automatic mechanism for mirror operators to keep their mirror online and updated, but indicate that it should stop being used due to maintenance or end of life shutdown. The mirror sync infrastructure is extra hardware that the Debian project needs to buy (since we no longer have server vendors giving us gratis hardware like HP/HPE used to) and that DSA need to find hosting for and maintain and that the mirror team (which is just DSA right now) need to setup and maintain syncing on. The support for https within the mirror network is spotty and the mirror monitoring infrastructure doesn't check for https support. OTOH https only provides minimal obscurity for traffic, since all the file sizes are known, a passive observer could correlate request size with individual packages, especially for larger ones. For mirrors there is a wider distribution of sizes due to mirrors of other distros on the same domain names as the Debian mirrors, so it is harder to correlate. PS: the mirror monitoring service: https://mirror-master.debian.org/status/mirror-hierarchy.html https://salsa.debian.org/mirror-team/status PS: personally I just use the CDN everywhere, since I don't have to make a choice, I don't have a bandwidth quota, my ISP's Debian mirror was always terrible, my ISP dropped its Debian mirror and some of my devices move between networks. -- bye, pabs https://wiki.debian.org/PaulWise
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