backend write error: 35

Angelo Höngens A.Hongens at
Mon Apr 19 20:27:55 CEST 2010

After rolling back from 2.1.0 to 2.0.5 (because of #678), at least my balancers stayed up throughout the weekend. So I'm happy again, and until it's sorted out, I'm staying on 2.0.x.

Today I've noticed some other strange stuff though, where images on some domains gave 503's. No idea when that started. I don't see anything strange on the backend (haproxy listening on multiple ports on localhost), and I only saw 200's being retrieved by varnish. Varnishlog showed the error "FetchError c http read error: 0". No idea what it means, but googling it, I saw ticket #624, talking about http 1.1 vs http 1.0 and httpcloses. I don't think it's relevant, since I only see http 1.1 requests and responses. Does anyone know what this "http read error: 0" error means?

Inspired though, I saw I set haproxy to force client connections to disconnect (global option httpclose). I turned it off, and now varnish reuses connections to haproxy, and the "http read error: 0" suddenly disappears.

(FYI: My setup: I have varnish running on a box, and based on the 8900 different hostnames, it selects one of the 325 backends. These backends are all haproxy listeners, listening on localhost:8001, localhost:8002, etc..

The fact that using keepalives to the backends solves that message, gives me the feeling I might be running into problems with the number of tcp sockets available on my localhost interface or something like that. Should I be able to see any indication of this on my bsd boxes? I don't see anything strange in my messages.log or the like. I don't see that many connections using netstat:

$ netstat -an | grep 127.0.0 | awk '{print $6}' | sort -n | uniq -c
  23 FIN_WAIT_2

However, that seems to be solved for now as well. Now however, I get yet another error I did not get (that much) before. I now have some post requests (that are being passed) that show: 

FetchError   c backend write error: 35

Any idea what this error means?


With kind regards,
Angelo Höngens
Systems Administrator
tourism internet software solutions
Ringbaan Oost 2b
5013 CA Tilburg
T: +31 (0)13 5811088
F: +31 (0)13 5821239
mailto:A.Hongens at

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