Traffic drop issue

[Sébastien EISSLER]

Hello,

We encounter an issue on trafic increase event, here is the timeline:

- We have normally ~1000 req/s, a event cause the traffic to increase to ~1400 req/s with spike at ~2300.
- Varnish is creating new threads to the limit
- threads_limited counter strongly increase
- Varnish don't response to all requests, req/s decrease slowly to 0 (see attachment)
- A restart of Varnish solved the problem, varnish accept all requests.

Can you help us identify the problem? Do you need to adjust the configuration?
You can find a param.show in attachement.

# varnishd -V
varnishd (varnish-6.4.0 revision 13f137934ec1cf14af66baf7896311115ee35598)
Copyright (c) 2006 Verdens Gang AS
Copyright (c) 2006-2020 Varnish Software AS

We use hitch for TLS support:

# hitch -V
hitch 1.5.2

Best Regards,
-- 
Sébastien 
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