varnish 2.0.4 backend errors

[Lazy]

2009/7/14 Ken Brownfield <kb at slide.com>:
> The progression from your dump is:
>
> Varnish         Apache
> SYN
>                SYN+ACK
> ACK
> ...4.4 seconds later...
>                SYN+ACK
> ACK
> PSH+ACK
>                ACK
> FIN+ACK (???)
>                PSH+ACK
> RST

right i missed the 4second gap, so varnish may be hitting a timeout

>
> It looks like the ACK from the Varnish side is getting lost on its way to
> Apache, and Apache retransmits.  This itself would imply that you have some
> packet loss between Varnish and Apache.  That 4.4 second delay could easily
> be running you against the sess_timeout (or cli_timeout, maybe).  Bumping
> those up to 10 might clear the issue for you.
>
> Obviously, packet loss will cause issues in general, so I'd investigate that
> anyway.
it's a local interface, not lo but the traffic is going threw loopback interface

>
> More bizarrely, that FIN+ACK is missing a FIN from Apache.  Are you sure
> this stream is correct?  I have no idea what would cause a spurious FIN+ACK
> (besides a spurious FIN) and the issue would be highly unlikely a Varnish
> issue; more likely a kernel TCP stack issue.
>
> Is there anything between Varnish and Apache in your config, besides two
> machines on a shared switch?  Proxies?  Firewall rules?  Switch ACLs?  What
> OSes/versions are you running on each side?

it's only 1 machine