Nginx returns HTTP 200 with Content-Length: 0

[apeman]

no, no, no!
Normally, it's not 0, but sometimes, the possibility is 0.07%. It's
absolutely not normal!
[21/May/2013:00:02:56 +0800] "POST /ourservice/api HTTP/1.1" 200 607 27 "-"
"c" "10.23.130.154"  
[21/May/2013:00:02:56 +0800] "POST /ourservice/api HTTP/1.1" 200 613 27 "-"
"c" "10.59.24.83"    
[21/May/2013:00:02:56 +0800] "POST /ourservice/api HTTP/1.1" 200 604 62 "-"
"e" "10.197.218.20"  
[21/May/2013:00:02:57 +0800] "POST /ourservice/api HTTP/1.1" 200 491 27 "-"
"f" "-"              
[21/May/2013:00:02:57 +0800] "POST /ourservice/api HTTP/1.1" 200 612 278 "-"
"f" "10.165.21.34"  
[21/May/2013:00:02:57 +0800] "POST /ourservice/api HTTP/1.0" 200 816 27 "-"
"c" "10.26.152.101"  
[21/May/2013:00:02:57 +0800] "POST /ourservice/api HTTP/1.1" 200 585 27 "-"
"c" "10.67.55.190"   
[21/May/2013:00:02:57 +0800] "POST /ourservice/api HTTP/1.1" 200 463 211 "-"
"f" "-"             
[21/May/2013:00:02:57 +0800] "POST /ourservice/api HTTP/1.1" 200 596 0 "-"
"f" "10.181.30.95"    
You see the last column, the response content-length is 0. And we can't find
the record in tomcat log. It seems nginx don't forward the request to
tomcat.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,205826,239408#msg-239408