我们收到来自Varnish的随机503响应，当我们深入了解varnishlog时，我们看到后端服务器（Apache）被报告为503，但是apache访问日志中没有任何内容。
我们如何追查这个问题的原因？
来自varnishlog
* << Request >> 42221068
- Begin req 42221065 rxreq
- Timestamp Start: 1553163507.132639 0.000000 0.000000
- Timestamp Req: 1553163507.132639 0.000000 0.000000
- ReqStart 172.31.19.159 14390
- ReqMethod POST
- ReqURL /path/to/request
- ReqProtocol HTTP/1.1
- ReqHeader X-Forwarded-For: 62.103.214.39
- ReqHeader X-Forwarded-Proto: https
- ReqHeader X-Forwarded-Port: 443
- ReqHeader Host: server.com
- ReqHeader X-Amzn-Trace-Id: Root=1-5c9364f3-26a603e3ce2f87d9923ed27e
- ReqHeader Content-Length: 53
- ReqHeader Accept: application/json
- ReqHeader Authorization: Bearer xxx
- ReqHeader Content-Type: application/json; charset=utf-8
- ReqHeader Cookie: PHPSESSID=o1f3010cuch8iu055stl6q1s03
- ReqUnset X-Forwarded-For: 62.103.214.39
- ReqHeader X-Forwarded-For: 62.103.214.39, 172.31.19.159
- VCL_call RECV
- VCL_return pass
- VCL_call HASH
- VCL_return lookup
- VCL_call PASS
- VCL_return fetch
- Link bereq 42221069 pass
- Storage malloc Transient
- Timestamp ReqBody: 1553163507.952175 0.819536 0.819536
- Timestamp Fetch: 1553163507.952297 0.819659 0.000123
- RespProtocol HTTP/1.1
- RespStatus 503
- RespReason Backend fetch failed
- RespHeader Date: Thu, 21 Mar 2019 10:18:27 GMT
- RespHeader Server: Varnish
- RespHeader Content-Type: text/html; charset=utf-8
- RespHeader Retry-After: 5
- RespHeader X-Varnish: 42221068
- RespHeader Age: 0
- RespHeader Via: 1.1 varnish (Varnish/5.2)
- VCL_call DELIVER
- RespUnset Age: 0
- RespUnset Server: Varnish
- RespUnset X-Varnish: 42221068
- RespUnset Via: 1.1 varnish (Varnish/5.2)
- VCL_return deliver
- Timestamp Process: 1553163507.952322 0.819683 0.000024
- RespHeader Content-Length: 285
- RespHeader Connection: keep-alive
- Timestamp Resp: 1553163507.952341 0.819703 0.000020
- ReqAcct 415 53 468 194 285 479
- End
** << BeReq >> 42221069
-- Begin bereq 42221068 pass
-- Timestamp Start: 1553163507.132720 0.000000 0.000000
-- BereqMethod POST
-- BereqURL /path/to/request
-- BereqProtocol HTTP/1.1
-- BereqHeader X-Forwarded-Proto: https
-- BereqHeader X-Forwarded-Port: 443
-- BereqHeader Host: server.com
-- BereqHeader X-Amzn-Trace-Id: Root=1-5c9364f3-26a603e3ce2f87d9923ed27e
-- BereqHeader Content-Length: 53
-- BereqHeader Accept: application/json
-- BereqHeader Authorization: Bearer 3pa8ot18dlmpad2s34a5gt3p08jg0ml5
-- BereqHeader Content-Type: application/json; charset=utf-8
-- BereqHeader Cookie: PHPSESSID=o1f3010cuch8iu055stl6q1s03
-- BereqHeader X-Forwarded-For: 62.103.214.39, 172.31.19.159
-- BereqHeader X-Varnish: 42221069
-- VCL_call BACKEND_FETCH
-- VCL_return fetch
-- BackendOpen 32 reload_20190304_175528_18074.live1 172.31.11.111 8081 172.31.31.198 39914
-- BackendStart 172.31.11.111 8081
-- Timestamp Bereq: 1553163507.952205 0.819485 0.819485
-- FetchError HTC status -1
-- BackendClose 32 reload_20190304_175528_18074.live1
-- Timestamp Beresp: 1553163507.952235 0.819514 0.000029
-- Timestamp Error: 1553163507.952237 0.819517 0.000003
-- BerespProtocol HTTP/1.1
-- BerespStatus 503
-- BerespReason Service Unavailable
-- BerespReason Backend fetch failed
-- BerespHeader Date: Thu, 21 Mar 2019 10:18:27 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, 21 Mar 2019 10:18:27 GMT
-- ObjHeader Server: Varnish
-- ObjHeader Content-Type: text/html; charset=utf-8
-- ObjHeader Retry-After: 5
-- Length 285
-- BereqAcct 451 53 504 0 0 0
-- End
根据我们的理解，Varnish报告来自Apache的连接已关闭（EOF），但Apache再次没有报告任何内容。
我们需要以某种方式深究这一点，因为它正在影响服务协议。
有关追踪和解决问题的任何想法？
您没有Apache访问日志，因为Apache之前没有完全处理请求，因为之前存在问题。
这种问题可能导致这种情况：
在哪里可以寻找痕迹：