I am running a drupal 7 website on a Linux server (with 4 cores and 12GB RAM) with LEMP (nginx+php5-fpm+mysql). The drupal installation has a large number of modules enabled(all of which are needed). I also use apc + boost + memcache + authcache for caching. The caching seems to be working (i see pages being served from cache) and the site has a reasonable response time. I have run stress tests with the website running in a url like www-1.example.com. (www-1.example.com points to the ip of my webserver, let's say x.x.x.x) and the results are fine (for up to 100 concurrent users) The problem starts when I change the dns so that www.example.com also points to x.x.x.x. Then the cpu of my webserver (all 4 cores) reach 100% at short time. I have been expereimenting with the following parameters on the www.conf file with no luck:
pm.max_children = 100 pm.start_servers = 20 pm.min_spare_servers = 10 pm.max_spare_servers = 20 pm.max_requests = 200
result: 100% cpu usage, low memory usage
pm.max_children = 300 pm.start_servers = 20 pm.min_spare_servers = 10 pm.max_spare_servers = 20 pm.max_requests = 200
result: low cpu usage, 100% memory usage
Can anyone guide me to find the optimal comfiguration or has any idea on what can cause the 100% cpu usage? How do i culculate the maximum number of concurrent usages that can run without problem based on server parameters?