Thank you for the Reply Howard.
Client conducts almost 1000 batches at different locations and each batch is of 15 users. So in total almost 15000 users using Moodle and taking their quiz at the same.
APC and OPCache are configured properly and also allocated 10GB for APC. And we are able to see the hits on APC too. And coming to monitoring servers, we observed very low CPU usage and LOW RAM usage. Users are timedout after 20 secs.
Since Apache 2.4 is not allowing us to configure mpm_worker module, we configured mpm_prefork with below settings, we need someone to validate these "prefork" setting.
The error we are receiving while configuring mpm_worker module is given below, any idea on how to fix this issue may also help us to some extent.
AH00526: Syntax error on line 31 of /etc/httpd/conf.d/php.conf:
Invalid command 'php_value', perhaps misspelled or defined by a module not included in the server configuration
We are about to make session persistence / sticky session with round robin on load balancer so that a user hits the same app server till session timeouts. And also moving cache to local app servers from NFS and will keep only "filedir" and "session" directories on NFS as is.
Hope this helps in understanding our current configuration.