[tor-bugs] #24506 [Core Tor/Torflow]: Move some bandwidth authority servers to a CDN

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#24506: Move some bandwidth authority servers to a CDN
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 Reporter:  teor              |          Owner:  tom
     Type:  task              |         Status:  new
 Priority:  Medium            |      Milestone:
Component:  Core Tor/Torflow  |        Version:
 Severity:  Normal            |     Resolution:
 Keywords:  tor-bwauth        |  Actual Points:
Parent ID:  #24499            |         Points:
 Reviewer:                    |        Sponsor:
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Comment (by teor):

 This is a fundamental issue with the design of the bandwidth authority
 system: it measures both bandwidth and latency. (See #24506 and
 [https://trac.torproject.org/projects/tor/wiki/doc/BandwidthAuthorityMeasurements
 BandwidthAuthorityMeasurements].)

 It's already an issue with the existing locations of bandwidth scanners
 and bandwidth servers: nearby relays are rated higher than other relays.
 This is a big issue when there are only 5 scanners and 6 servers. Using a
 CDN actually makes this better, because it makes sure that more relays are
 close to one of the CDN bandwidth servers. (Fastly would give us about 20
 CDN locations.)

 And I don't think this issue will be as bad as you think:
 * bandwidth scanners build a two-hop path to the bandwidth server like
 this: scanner - entry - exit - server. So most paths will involve an entry
 that isn't in a CDN data center, and
 * even if some paths are all in the same data center, the bandwidth
 aggregator doesn't take the lowest value, it takes a combination of all
 the measured values.

 To mitigate this issue, we should:
 * make sure that the scanner isn't in one of the CDN data centers,
 * use different CDNs for different scanners,
 * use CDNs in combination with other bandwidth servers that aren't in one
 of the CDN data centers.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24506#comment:2>
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