This question already has an answer here:
a few days ago my Apache server randomly started hogging the CPU during which time the site becomes sluggish and unresponsive.
Here is what mod_status shows during an incident:
- Nearly all connections are in the waiting state
- A few connections are in the Keep-Alive state. All of them have Req column values (Milliseconds required to process most recent request) between 15 and 40 seconds, which is 10-20x longer than usual
- During this time, running top command shows 100% usage of all 4 CPUs, with 5-7 Apache child processes on top, taking 10-40% percent CPU each
Each incident lasts 15-30 minutes and then the situation returns to normal for a while, until another incident occurs.
Server configuration and stats:
- Digital Ocean droplet with 4 CPU's, 8 GB RAM
- LAMP stack running a Wordpress site, about 40K hits per day (XMLRPC protected, wp-login protected)
- MySQL performance appears normal (slow query logging on, nothing unusual)
Any advice on debugging this would be appreciated as I don't even know where to start.
Server Version: Apache/2.4.7 (Ubuntu) PHP/5.5.9-1ubuntu4.11 Server MPM: prefork Server Built: Jul 24 2015 17:25:11 Current Time: Sunday, 02-Oct-2016 08:41:09 EDT Restart Time: Sunday, 02-Oct-2016 07:55:53 EDT Parent Server Config. Generation: 1 Parent Server MPM Generation: 0 Server uptime: 45 minutes 15 seconds Server load: 105.26 38.36 22.87 Total accesses: 32705 - Total Traffic: 367.2 MB CPU Usage: u455.08 s51.66 cu0 cs0 - 18.7% CPU load 12 requests/sec - 138.5 kB/second - 11.5 kB/request 144 requests currently being processed, 39 idle workers _WWWWWWWWW_WKWWWWW__WWWW._WW.WWWW___W.WWWW__WWW_W_WWWW_WW.W_WWWW _W.WCWW_WW.WKWWWWWWWWW_WWWKW.W_K_.KW__K.W._WWWWW__WWWWWWWWW._WKW WWWK.WW_WW__WWWWWWWW__WWW_WWWW_WWWWWW_._WWWKK___WWW_WWWWWWWWWWWW _.W..WW. Scoreboard Key: "_" Waiting for Connection, "S" Starting up, "R" Reading Request, "W" Sending Reply, "K" Keepalive (read), "D" DNS Lookup, "C" Closing connection, "L" Logging, "G" Gracefully finishing, "I" Idle cleanup of worker, "." Open slot with no current process