After debugging for 6-hours - I am giving this up :| We have a nginx+php-fpm+mysql in LAN with almost 100 wordpress (created and used by different designers/developers all working on test wordpres setup) We are using nginx without any issues from long. Today, all of a sudden - nginx started returning "504 Gateway Time-out" out of the blue... I checked nginx error log for a virtual host... 2010/09/06 21:24:24 [error] 12909#0: *349 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 192.168.0.1, server: rahul286.rtcamp.info, request: "GET /favicon.ico HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "rahul286.rtcamp.info" 2010/09/06 21:25:11 [error] 12909#0: *349 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: 192.168.0.1, server: rahul286.rtcamp.info, request: "GET /favicon.ico HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "rahul286.rtcamp.info" 2010/09/06 21:25:11 [error] 12909#0: *443 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: 192.168.0.1, server: rahul286.rtcamp.info, request: "GET /info.php HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "rahul286.rtcamp.info" 2010/09/06 21:25:12 [error] 12909#0: *443 connect() failed (111: Connection refused) while connecting to upstream, client: 192.168.0.1, server: rahul286.rtcamp.info, request: "GET /favicon.ico HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "rahul286.rtcamp.info" 2010/09/06 22:08:32 [error] 12909#0: *1025 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 192.168.0.1, server: rahul286.rtcamp.info, request: "GET / HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "rahul286.rtcamp.info" 2010/09/06 22:09:33 [error] 12909#0: *1025 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 192.168.0.1, server: rahul286.rtcamp.info, request: "GET /favicon.ico HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "rahul286.rtcamp.info" 2010/09/06 22:09:40 [error] 12909#0: *1064 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: 192.168.0.1, server: rahul286.rtcamp.info, request: "GET /info.php HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "rahul286.rtcamp.info" 2010/09/06 22:09:40 [error] 12909#0: *1064 connect() failed (111: Connection refused) while connecting to upstream, client: 192.168.0.1, server: rahul286.rtcamp.info, request: "GET /favicon.ico HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "rahul286.rtcamp.info" 2010/09/06 22:24:44 [error] 12909#0: *1313 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 192.168.0.1, server: rahul286.rtcamp.info, request: "GET / HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "rahul286.rtcamp.info" 2010/09/06 22:24:53 [error] 12909#0: *1313 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: 192.168.0.1, server: rahul286.rtcamp.info, request: "GET /favicon.ico HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "rahul286.rtcamp.info" As I run php-fpm on port 9000 via TCP mode, I ran "netstat | grep 9000" and noticed something unusual... (Pasting partial output here for ease of read) tcp 9 0 localhost:9000 localhost:36094 CLOSE_WAIT 14269/php5-fpm tcp 0 0 localhost:46664 localhost:9000 FIN_WAIT2 - tcp 1257 0 localhost:9000 localhost:36135 CLOSE_WAIT - tcp 1257 0 localhost:9000 localhost:36125 CLOSE_WAIT - tcp 9 0 localhost:9000 localhost:36102 CLOSE_WAIT 14268/php5-fpm tcp 0 0 localhost:46662 localhost:9000 FIN_WAIT2 - tcp 745 0 localhost:9000 localhost:46644 CLOSE_WAIT - tcp 0 0 localhost:46658 localhost:9000 FIN_WAIT2 - tcp 1265 0 localhost:9000 localhost:46607 CLOSE_WAIT - tcp 0 0 localhost:46672 localhost:9000 ESTABLISHED 12909/nginx: worker tcp 1257 0 localhost:9000 localhost:36119 CLOSE_WAIT - tcp 1265 0 localhost:9000 localhost:46613 CLOSE_WAIT - tcp 0 0 localhost:46646 localhost:9000 FIN_WAIT2 - tcp 1257 0 localhost:9000 localhost:36137 CLOSE_WAIT - tcp 0 0 localhost:46670 localhost:9000 ESTABLISHED 12909/nginx: worker tcp 1265 0 localhost:9000 localhost:46619 CLOSE_WAIT - tcp 1336 0 localhost:9000 localhost:46668 ESTABLISHED - tcp 0 0 localhost:46648 localhost:9000 FIN_WAIT2 - tcp 1336 0 localhost:9000 localhost:46670 ESTABLISHED - tcp 9 0 localhost:9000 localhost:36108 CLOSE_WAIT 14274/php5-fpm tcp 1336 0 localhost:9000 localhost:46684 ESTABLISHED - tcp 0 0 localhost:46674 localhost:9000 ESTABLISHED 12909/nginx: worker tcp 1336 0 localhost:9000 localhost:46666 ESTABLISHED - tcp 1257 0 localhost:9000 localhost:46648 CLOSE_WAIT - tcp 1336 0 localhost:9000 localhost:46678 ESTABLISHED - tcp 0 0 localhost:46668 localhost:9000 ESTABLISHED 12909/nginx: wo There are plenty of "CLOSE_WAIT" & "FIN_WAIT2" pairs as highlighted below (in above output): tcp 1337 0 localhost:9000 localhost:46680 CLOSE_WAIT - tcp 0 0 localhost:46680 localhost:9000 FIN_WAIT2 - Please note port 46680 in above. I enabled mysql slow queries error log, but it didn't work. As of now restarting php5-fpm every minute via a cronjob (see command below) keeping everything running "smoothly" but I hate patchwork and want to solve this... 1 * * * * service php5-fpm restart > /dev/null I searched extensively on Google - got no help. As mentioned, this a test-server in LAN, CPU load is never crossed 0.10 and memory usage is also below 25% (System has 2GB RAM and ubuntu-server installed) So if you find its time-confusing to help me out, please atleast drop a hint. Thanks in advance for help. -Rahul (note - this is reposting of - http://forum.nginx.org/read.php?11,127694) Update: I found answer, which is posted below.