"http first read error: EOF" errors from WordPress backend

[Hazar Güney]

Hello,

>From a backend with Apache+WordPress, we occasionally see "http first read
error: EOF" errors. This situation is different then my first question
because this time it seems that Varnish waits for 60 seconds from backend.
According to Apache access log, backend responds to the request from
Varnish less than 1 second which is very strange.

(We are 3 hours ahead of GMT)

*Backend:*

[31/Mar/2017:02:25:29 +0300] "GET XXXX HTTP/1.1" 200 22575

*Varnish:*

*   << BeReq    >> 3684412
-   Begin          bereq 3684411 fetch
-   Timestamp      Start: 1490916329.664410 0.000000 0.000000
-   BereqMethod    GET
-   BereqURL       XXXX
-   BereqProtocol  HTTP/1.1
-   BereqHeader    Host: XXXX
-   BereqHeader    Accept:
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
-   BereqHeader    From: googlebot(at)googlebot.com
-   BereqHeader    User-Agent: Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5X
Build/MMB29P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.96
Mobile Safari/537.36 (compatible; Googlebot/2.1; +
http://www.google.com/bot.html)
-   BereqHeader    RIP: 66.249.66.227
-   BereqHeader    X-Forwarded-For: XXXX
-   BereqHeader    Accept-Encoding: gzip
-   BereqHeader    X-Varnish: 3684412
-   VCL_call       BACKEND_FETCH
-   VCL_return     fetch
-   BackendOpen    21 reload_2017-03-21T100643.default 10.35.78.153 80
172.17.0.2 56104
-   BackendStart   XXXX 80
-   Timestamp      Bereq: 1490916329.664853 0.000443 0.000443
*-   FetchError     http first read error: EOF*
-   BackendClose   21 reload_2017-03-21T100643.default
-   Timestamp      Beresp: 1490916389.664967 *60.000557* 60.000114
-   Timestamp      Error: 1490916389.664978 *60.000567 *0.000011
-   BerespProtocol HTTP/1.1
-   BerespStatus   503
-   BerespReason   Service Unavailable
-   BerespReason   Backend fetch failed
-   BerespHeader   Date: Thu, 30 Mar 2017 23:26:29 GMT
-   BerespHeader   Server: Varnish
-   VCL_call       BACKEND_ERROR
-   BerespHeader   Content-Type: text/html; charset=utf-8
-   BerespHeader   Retry-After: 5
-   VCL_return     deliver
-   Storage        malloc Transient
-   ObjProtocol    HTTP/1.1
-   ObjStatus      503
-   ObjReason      Backend fetch failed
-   ObjHeader      Date: Thu, 30 Mar 2017 23:26:29 GMT
-   ObjHeader      Server: Varnish
-   ObjHeader      Content-Type: text/html; charset=utf-8
-   ObjHeader      Retry-After: 5
-   Length         284
-   BereqAcct      509 0 509 0 0 0
-   End

*   << Request  >> 3684411
-   Begin          req 3684410 rxreq
-   Timestamp      Start: 1490916329.664345 0.000000 0.000000
-   Timestamp      Req: 1490916329.664345 0.000000 0.000000
-   ReqStart       XXXX 45415
-   ReqMethod      GET
-   ReqURL         XXXX
-   ReqProtocol    HTTP/1.1
-   ReqHeader      Host: XXXX
-   ReqHeader      Connection: Keep-alive
-   ReqHeader      Accept:
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
-   ReqHeader      From: googlebot(at)googlebot.com
-   ReqHeader      User-Agent: Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5X
Build/MMB29P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.96
Mobile Safari/537.36 (compatible; Googlebot/2.1; +
http://www.google.com/bot.html)
-   ReqHeader      RIP: 66.249.66.227
-   ReqHeader      X-Forwarded-For: XXXX
-   VCL_call       RECV
-   VCL_return     hash
-   VCL_call       HASH
-   VCL_return     lookup
-   VCL_call       MISS
-   VCL_return     fetch
-   Link           bereq 3684412 fetch
-   Timestamp      Fetch: 1490916389.665129 60.000784 60.000784
-   RespProtocol   HTTP/1.1
-   RespStatus     503
-   RespReason     Backend fetch failed
-   RespHeader     Date: Thu, 30 Mar 2017 23:26:29 GMT
-   RespHeader     Server: Varnish
-   RespHeader     Content-Type: text/html; charset=utf-8
-   RespHeader     Retry-After: 5
-   RespHeader     X-Varnish: 3684411
-   RespHeader     Age: 0
-   RespHeader     Via: 1.1 varnish-v4
-   VCL_call       DELIVER
-   VCL_acl        NO_MATCH hitpass
-   RespUnset      Via: 1.1 varnish-v4
-   RespUnset      X-Varnish: 3684411
-   VCL_return     deliver
-   Timestamp      Process: 1490916389.665181 60.000836 0.000052
-   RespHeader     Content-Length: 284
-   Debug          "RES_MODE 2"
-   RespHeader     Connection: keep-alive
-   Timestamp      Resp: 1490916389.665241 60.000896 0.000060
-   ReqAcct        461 0 461 200 284 484
-   End
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