Intermittent 400 error code -client sent invalid method while reading client request line,

[paphillon]

In our setup we have a client that makes some web services calls to the
back end with nginx as a proxy in between.

Most of the time it is successful 99%  but 1% calls are dropped and the
client reports the error. On retry the operation goes through fine, no
other change is requried.

The client is on a hosted environment, so getting detailed logs from
client is bit hard.

(Client Error) --- Error: unable to send request to :
https://proxt.nginx.host.url. Server response:
System.HttpResponse[Status=null, StatusCode=-1]

Nginx captures the below in the default server error log. Interestingly
no access / error log is written for the virtual host that is suppose to
handle the request.

2012/06/26 20:22:55 [debug] 32536#0: *305 http check ssl handshake
2012/06/26 20:22:55 [debug] 32536#0: *305 https ssl handshake: 0x16
2012/06/26 20:22:55 [debug] 32536#0: *305 http process request line
2012/06/26 20:22:55 [debug] 32536#0: *305 http process request line
2012/06/26 20:22:55 [info] 32536#0: *305 client sent invalid method
while reading client request line, client: 96.43.x.x, server: , request:
"User-Agent: Java/1.6.0_21"
2012/06/26 20:22:55 [debug] 32536#0: *305 http finalize request: 400,
"?" a:1, c:1
2012/06/26 20:22:55 [debug] 32536#0: *305 http special response: 400,
"?"
2012/06/26 20:22:55 [debug] 32536#0: *305 http set discard body
2012/06/26 20:22:55 [debug] 32536#0: *305 headers more header filter,
uri ""
2012/06/26 20:22:55 [debug] 32536#0: *305 http output filter "?"
2012/06/26 20:22:55 [debug] 32536#0: *305 http copy filter: "?"
2012/06/26 20:22:55 [debug] 32536#0: *305 http postpone filter "?"
000000001C39D958
2012/06/26 20:22:55 [debug] 32536#0: *305 http write filter: l:1 f:0
s:166
2012/06/26 20:22:55 [debug] 32536#0: *305 http write filter limit 0
2012/06/26 20:22:55 [debug] 32536#0: *305 http write filter
0000000000000000
2012/06/26 20:22:55 [debug] 32536#0: *305 http copy filter: 0 "?"
2012/06/26 20:22:55 [debug] 32536#0: *305 http finalize request: 0, "?"
a:1, c:1
2012/06/26 20:22:55 [debug] 32536#0: *305 http lingering close handler
2012/06/26 20:22:55 [debug] 32536#0: *305 lingering read: 0
2012/06/26 20:22:55 [debug] 32536#0: *305 http request count:1 blk:0
2012/06/26 20:22:55 [debug] 32536#0: *305 http close request
2012/06/26 20:22:55 [debug] 32536#0: *305 http log handler
2012/06/26 20:22:55 [debug] 32536#0: *305 close http connection: 10

Any pointers?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,227966,227966#msg-227966