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.