Re: New Version Notification for draft-kazuho-httpbis-selftrace-00.txt

[Jana Iyengar <[e-mail]>]

Matt,

Both good points. These are limitations of this approach (and can be noted
in the document), but I don't know how you can get around these issues
using this mechanism.

For the HS issue, Robin suggested using a TP, and while specifying the
mechanism is easy, I'm not sure how useful it will be given that there's no
easy way to trigger that on a browser or web clients.

For CC/FC issues, you could ignore CC for specifically sending a message
that says "my available cwnd is 0", but you can't get around FC, since you
violate FC at the receiver and risk getting the connection closed. While
these  signals are useful, you can also infer them in 2 other ways:
(i) you stopped receiving data and traces. Presumably a client-side trace
can be gathered which should show BLOCKED frames being received.
(ii) it isn't too difficult to see a diminishing cwnd or rwnd in the trace
that has been received prior to getting blocked.

- jana

On Fri, Aug 13, 2021 at 9:50 AM Matt Joras <[e-mail]> wrote:

> Happy to see this work! Speaking as an individual:
>
> One limitation of this sort of scheme (HTTP triggering and utilizing the
> same connection) is that it won't be able to capture two classes of issues
> that can be very problematic: handshake setup issues and mid-connection
> "stalling" issues. The former I think it's pretty obvious why, as this
> trace is triggered by an HTTP signal. As an example of the latter, consider
> a bug where the server runs down its flow control or congestion control to
> zero and can't recover. This ends up with the server being perpetually
> blocked from sending anything, and both endpoints idle timing out. If a
> client wants to trigger a trace and reproduce the issue then it will end up
> not getting a trace at all, since the server is stuck. That's not to say
> this kind of tracing isn't useful for other classes of issues, but these
> are two serious ones we've had to diagnose with "out of band"
> non-HTTP-triggered qlogs, and I wonder if we should also explore a
> standardized mechanism for triggering those kind of traces.
>
> Matt
>
> On Fri, Aug 13, 2021 at 12:15 AM Kazuho Oku <[e-mail]> wrote:
>
>> Hello folks,
>>
>> Today Jana and I have submitted a tiny I-D called
>> draft-kazuho-httpbis-selftrace.
>>
>> The draft specifies a well-known URI to be used for providing a trace of
>> a particular HTTP/3 connection (e.g., qlog) on that same HTTP/3 connection.
>>
>> One of the biggest hurdles in analyzing HTTP/3 performance issues is
>> obtaining traces that show the symptoms. That is because clients being
>> affected by issues have to coordinate with the server operators to collect
>> the traces.
>>
>> This PR solves the problem by defining a well-known URI for serving a
>> trace to the client on the HTTP connection that the client is using. When a
>> user sees an issue, they can collect the traces themselves and provide it
>> to the server operator.
>>
>> We have already implemented the feature in h2o, and doing so was easy,
>> assuming that the underlying QUIC stack already defines callbacks for
>> collecting trace events, see lib/handler/self_trace.c of
>> https://github.com/h2o/h2o/pull/2765.
>>
>> We also have a public endpoint; to try it out, first open
>> https://ora1.kazuhooku.com/test/self-trace/video-only.html (which starts
>> streaming a video), then open
>> https://ora1.kazuhooku.com/.well-known/self-trace. While the video is
>> being served, you would see the trace flowing through the well-known URI.
>>
>> At the moment, we are using a custom JSON format for the trace, but when
>> gzip compression is applied on-the-fly, the overhead of sending a trace
>> alongside ordinary HTTP responses is less than 10%. Therefore, we tend to
>> believe that this approach would work well in practice.
>>
>> Please let us know what you think - your feedback is very welcome.
>>
>> ---------- Forwarded message ---------
>> From: <[e-mail]>
>> Date: 2021年8月13日(金) 14:53
>> Subject: New Version Notification for
>> draft-kazuho-httpbis-selftrace-00.txt
>> To: Jana Iyengar <[e-mail]>, Kazuho Oku <[e-mail]>
>>
>>
>>
>> A new version of I-D, draft-kazuho-httpbis-selftrace-00.txt
>> has been successfully submitted by Kazuho Oku and posted to the
>> IETF repository.
>>
>> Name:           draft-kazuho-httpbis-selftrace
>> Revision:       00
>> Title:          Self-Tracing for HTTP
>> Document date:  2021-08-13
>> Group:          Individual Submission
>> Pages:          5
>> URL:
>> https://www.ietf.org/archive/id/draft-kazuho-httpbis-selftrace-00.txt
>> Status:
>> https://datatracker.ietf.org/doc/draft-kazuho-httpbis-selftrace/
>> Htmlized:
>> https://datatracker.ietf.org/doc/html/draft-kazuho-httpbis-selftrace
>>
>>
>> Abstract:
>>    This document registers a "Well-Known URI" for exposing state of an
>>    HTTP connection to the peer using formats such as qlog schema [QLOG].
>>
>>
>>
>>
>> The IETF Secretariat
>>
>>
>>
>>
>> --
>> Kazuho Oku
>>
>