Assert error in VPX_Send_Proxy()

[Christopher Beppler]

Hi,

I am new to this list and I hope that someone here can shed some light
on my issue. I have googled the error message but didn't find anything
related to VPX_Send_Proxy().

My setup is as follows:

Haproxy --(proxy-v2)-> varnish --(proxy-v1)-> nginx -> webapps

I am running FreeBSD 11.1-RELEASE-p4 and varnish5-5.2.1 from ports.

Since a few days, I get the following error message. Not all the time,
but always around the same time. So it might be an issue related to a
certain load:

Mar 14 23:44:04 varnish varnishd[15349]: Child (24895) Panic at: Wed, 14
Mar 2018 22:44:04 GMT Assert error in VPX_Send_Proxy(),
proxy/cache_proxy_proto.c line 425:   Condition((sp) != NULL) not true.
version = varnish-5.2.1 revision NOGIT, vrt api = 6.1 ident =
FreeBSD,11.1-RELEASE-p4,amd64,-junix,-sfile,-smalloc,-hcritbit,kqueue
now = 4710006.893845 (mono), 1521067443.500616 (real) Backtrace:
0x437e60: <PAN_Init+0x2f0> at /usr/local/sbin/varnishd   0x47e0bc:
<VAS_Fail+0x6c> at /usr/local/sbin/varnishd   0x46fb96:
<VPX_Send_Proxy+0x356> at /usr/local/sbin/varnishd   0x4173bf:
<VBE_fill_director+0x128f> at /usr/local/sbin/varnishd   0x4162f7:
<VBE_fill_director+0x1c7> at /usr/local/sbin/varnishd   0x43d184:
<CNT_Request+0x1cf4> at /usr/local/sbin/varnishd   0x458841:
<V1F_FetchRespHdr+0xd81> at /usr/local/sbin/varnishd   0x451f96:
<pool_herder+0x986> at /usr/local/sbin/varnishd   0x451d15:
<pool_herder+0x705> at /usr/local/sbin/varnishd thread = (cache-worker)
thr.req = 0x80f902ba0 {   vxid = 98306, transport

This results in a client disconnect. If I retry loading the page it
sometimes work.

If I am not mistaken, varnish kills a process/thread if an assertion
fails and spawns a new one to stay in a clean state. That's why I don't
have to restart anything. After some time, it seems to recover but
during the time this error appears the page is almost unusable.

Why question would now be what I can do to resolve that and what it
means that sp == NULL at this particular assertion?

If you need more logs or details, I am happy to provide them.

Thanks in advance,
Christopher