Query regarding "http first read error: EOF" error in varnish

[Geoff Simmons]

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On 01/13/2016 10:49 AM, Jayanth Kalyanasundaram wrote:
> Hello,
> 
> We are currently using varnish 4.1.0 as a caching layer on top of a
> few of our production servers, and from time to time we see a few
> 503 errors in the varnish log with the error "-   FetchError
> http first read error: EOF". The complete log for this is shared
> here: http://pastebin.com/JSqywXDa

"http first read error: EOF" means that there was a socket read error
while attempting to fetch the first chunk of the response header from
the connection to your backend, usually a first byte timeout or a
closed connection.

- -   Timestamp      Bereq: 1452675822.047840 0.015508 0.015508
- -   FetchError     http first read error: EOF
- -   BackendClose   232 reload_2016-01-12T07:28:50.cp_12
- -   Timestamp      Beresp: 1452675876.038544 54.006212 53.990704

This says that about 54 seconds elapsed after Varnish sent the backend
request until it gave up waiting for the response. That could very
well be a first byte timeout, especially since the waiting time is so
close to the round number 54 (although 54 seconds is an unusual value
for first_byte_timeout).

> The issue doesn't seem to be a connection problem with the backend 
> because a simple curl call of the same URL from the varnish box
> seems to work fine. So we'd like to know what could be the reason
> behind the error mentioned above and how we can fix it.

Does Varnish get the FetchError every time, or only sometimes? It
could have been that your curl tests were "just lucky".


HTH,
Geoff
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