We've got an "interesting" (read: worrying!) problem with our (fairly new) live Moodle setup.
Moodle 2.3.1 on SuSE Enterprise Linux based Apache 2.2.10 / PHP5 (x 4 servers). The moodledata area is on NFS.
Cisco ACE providing load balancing / system availability control / SSL offloading (SSL certificates are installed here)
PHP5 acceleration (xcache provided by PHP module php-xcache-1.3.2-2.32)
We're just ramping the usage up, as students are starting to return after their summer break. We're now routinely hitting 120 concurrent users, but this is set to spiral (hopefully not out of control...!) over the next few weeks.
The problems we're seeing are around response. This is just so unpredictable. We've managed to determine that it's not MySQL (at the moment!), but basically anything else in the application stack is up for questioning.
We can remove the Cisco load balancer, and thnings remain the same, so it's very probably not that either.
Interestingly, if we ping (nping) port 80 (which is the moodle port, as SSL offloading is done on the Cisco) then we'll get occasional packet loss. Port 443 works correctly 100% of the time.
So, does anyone have any advice with respect to tuning apache, TCP kernel parameter adjustments, etc?
Our suggested eventual level of concurrency is up to 2000 users logged in, probably 10% busy at any given time.
Thanks very much