508 Resource Limit Reached Error :
This error often comes to the domains which are hosted on CloudLinux server. On CloudLinux installed server every account has allotted a fixed amount of resources to use. This is just beacuse of CloudLinux installed server, as it uses LVE (Linux Virtualised Enviornments) which separate each accounts with their limits to use resources. This 508 Resource Limit Reached Error occurs when any account is excedding it's recources limit continously which are assigned to it. CloudLinux LVE helps to balance the hosting enviornment, as it monitors all user accounts and stops other user accounts to consume system resources when they excedding their limits.
Most Important Limiting factors :
SPEED : To set CPU limit SPEED is used. It is set in % of a single core of processor.
VMEM : Virtual memory limit, amount of momory allocation within LVE.
PMEM : Actual Physical memory allocation to user's account.
EP : Entry processes, this is the main factor behind "508 Resource Limit Is Reached" error.
NPROC : Number of process which can run in LVE. No new process can be created if limit is reached. It can be created if any other process dies.
IOPS : It limits total number of read/write operations per second.
Now, let discuss about EP(Entry Process). These are the connection which are made to a server through PHP script. That means all these are entering into LVE on Apache CloudLinux installed server. LVE limits the total number of EP to server so that a user's account doesn't use all resources. If limit reaches to maximum and exceeds it will give error "508 Resorce limit reached"
You can check this through your cPanel account : Login to cPanel >> Logs >> Resource usage
How to Fix this error ?
First and very important thing is to check whether the website is under any attack or not. Mostly websites under DOS attack gives this error. You can check your log files for more information.
If you are using Wordpress site then this may be due to to wp-login.php attack. You can harden your Wordpress websites through these simple steps.
You can remove/disable unused and not required plugins and themes. Optimize your database also.
You can increase EP limits in CloudLinux LVE if you see valid traffic increase on website : WHM Home >> Server Configuration >> CloudLinux LVE Manager >> Settings >> Edit >> Apply