varnish 5.0: varnish slow when backends do not respond?

[Guillaume Quintard]

Hi,

Do you have probes set up? If you do, the backend will be declared sick and
varnish will reply instantly without even trying to contact it.

It sounds like that at the moment, varnish just tries to get whatever it
can, waiting for as long as authorized.

Cheers,

On Tue, Feb 5, 2019, 11:51 Hu Bert <revirii at googlemail.com wrote:

> Hey there,
>
> i hope i'm right here... i have the following setup to deliver images:
>
> nginx: https -> forward request to varnish 5.0
> if image is not in cache -> forward request to backend nginx
> backend nginx: delivers file to varnish if found on harddisk
> if backend nginx doesn't find: forward request to 2 backend tomcats to
> calculate the desired image
>
> The 2 backend tomcats do deliver another webapp (and are a varnish
> backend as well); at the moment they're quite busy and stop working
> due to heavy load (->restart), the result is that varnish sees/thinks
> that the backends are sick. Somehow then even the cached images are
> delivered after a quite long waiting period, e.g. a 5 KB image takes
> more than 7 seconds.
>
> Is this the normal behaviour that varnish does answer slowly if some
> backends are sick?
>
> If any other information is need i can provide the necessary stuff.
>
> Thx in advance
> Hubert
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