cdn.netbsd.org incorrect cacheing setup wrt. pkgsrc INDEX

[Dmitry Marakasov <amdmi3@hades.panopticon>]

Hi!

I'm maintainer of Repology.org which regularly fetches pkgsrc INDEX [1]
in order to update data on pkgsrc packages, and I've run into a
problem with the way fastly-powered cdn.netbsd.org caches the file.
The problem is that it returns up old file to me, and it may be up to
a month old. The results may be seen on the graphs [2]: no updates are
seen until a file finally expired some days ago. Also there are rare
cases when new file is served.

The problem is rather hard to reproduce, as fastly seem to pick
different node when the file is requested from different hosts and
even different clients, and the file should be stuck in the cache
of the node you're requesting it from for the problem to be seen.
However it reproduces reliably for Repology with this command, which
is close to what Repology itself does:

python3 -c 'import requests; print(requests.get("https://cdn.netbsd.org/pub/pkgsrc/current/pkgsrc/INDEX";).headers["Age"])'

currently that returns 427839 which is around five days. I guess INDEX
has updated many times in that period.

My guess is that the problem may be reproduced from any host by issuing
the above command repeatedly for a long enough time Age will grow up to
1 month, and if you look into the contents, you'll see that this really
is and old INDEX.

I've written fastly [3], and they say that this behavior is expected
and suggest that this may be a misconfiguration which can be fixed by
NetBSD admins by reducing TTL setting. I've found a way to fix this for
Repology, which is adding an extra argument which changes with each request
(e.g. INDEX?time=<current timestamp>) which bypasses the cache and serves
the fresh file, but I worry that other pkgsrc consumers may hit this.

[1] https://cdn.netbsd.org/pub/pkgsrc/current/pkgsrc/INDEX
[2] https://repology.org/repository/pkgsrc_current
[3] https://community.fastly.com/t/cache-incorrectly-serving-old-content-under-specific-conditions/1249/3

-- 
Dmitry Marakasov   .   55B5 0596 FF1E 8D84 5F56  9510 D35A 80DD F9D2 F77D
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