[anti-censorship-team] Trying to understand multi-bridge dynamics post after Fastly/Cloudflare domain front change

[David Fifield]

On Tue, Oct 03, 2023 at 06:10:21PM +0000, David Fifield wrote:
> On Sun, Sep 24, 2023 at 09:38:33PM -0600, David Fifield wrote:
> > On Thu, Sep 21, 2023 at 09:26:58PM -0600, David Fifield wrote:
> > > I made a graph of the bandwidth on the two bridges since this started
> > > happening.
> > > 
> > > The two vertical lines mark:
> > > 2023-09-20 14:00:00	earliest known case of domain resolving to Cloudflare
> > > 2023-09-21 18:00:00	change to foursquare.com in rdsys
> > > 			https://gitlab.torproject.org/tpo/anti-censorship/rdsys-admin/-/merge_requests/17
> > > 
> > > 1. snowflake-02 bandwidth has dwindled to almost nothing. Seriously
> > >    almost nothing: it's around 3 MB/s currently.
> > > 2. There's a huge almost instantaneous step in snowflake-01 at around
> > >    2023-09-21 13:00:00. At first, I thought this might have been a
> > >    consequence of the rdsys change, but it's about 5 hours earlier than
> > >    that. What could it be? Some unrelated unblocking event that just
> > >    happened to happen while this domain stuff is happening?
> > 
> > The non-use of snowflake-02 continues -- see the attached graph. I'm
> > racking my brain trying to understand that is. snowflake-01 usage has
> > decreased a lot too -- the graph appears to be at about the same level,
> > but you can see it's not brickwalled at the upper end of the range as it
> > was before. Even ignoring the step anomaly at 2023-09-21 13:00:00, it
> > didn't go to zero like snowflake-02 did.
> 
> The snowflake-02 bridge is recovering, but very very slowly. It's now up
> to about 12 MB/s.

The plot thickens—after two weeks of very slow growth, the bandwidth on
snowflake-02 suddenly shot up to former levels over about 20 minutes
starting at 2023-10-04 11:40. See the attached graphics.

I don't have an explanation for it. snowflake-01 had rebooted about
4 hours earlier:
https://bugs.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/40292#note_2951293
(which accounts for the missing data in the snowflake-01 graph; I didn't
immediately restart the bandwidth monitor after the reboot).
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