Nginx + php-fpm "504 Gateway Time-out" error with almost zero load (on a test-server)

[minaev]

Rahul,

Backlog is explained in man listen(2):

The  backlog argument defines the maximum length to which the queue of
pending connections for sockfd
may grow.  If a connection request arrives when the queue is full, the
client may  receive  an  error
with  an  indication  of  ECONNREFUSED  or,  if  the underlying protocol
supports retransmission, the
request may be ignored so that a later reattempt at connection
succeeds.
...
If the backlog argument is greater  than  the  value  in 
/proc/sys/net/core/somaxconn,  then  it  is
silently  truncated  to that value; the default value in this file is
128.  In kernels before 2.4.25,
this limit was a hard coded value, SOMAXCONN, with the value 128.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,127854,128361#msg-128361