VSL Timeout and Varnishkafka

[Geoff Simmons]

On 06/22/2016 01:04 PM, Luca Toscano wrote:
> 
> Nice test that I found in the Varnish codebase (meant to trigger a
> VSL timeout):
> 
> https://github.com/varnishcache/varnish-cache/blob/4.1/bin/varnishtest/tests/r01762.vtc#L29

That's
> 
probably your best bet. Otherwise, triggering VSL timeouts can
be tricky, because there are a lot of things going on that are hard to
control.

You said that your PHP script sleeps before emitting "HTML" -- if
that's what you really meant, then your response probably sent
headers, and then went to sleep before sending the body. In that case,
there won't be a first_byte_timeout -- the timeout is until any part
of the response arrives, including headers.

You could try the same trick but with a large between_bytes_timeout.
Or find a way to send nothing at all, not even headers, until the
first_byte_timeout elapses.

I have in fact seen VSL timeouts in production as a result of
long-running responses, but if you want to reliably reproduce it that
way, try making the time differences very large -- say timeouts=150s,
and have your backend delay the response for five minutes.


HTH,
Geoff
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