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Understanding CloudLinux Resource Limits

by John Doe

Our shared hosting packages support the following CloudLinux resource limits:

Speed: CPU speed limit, relative to a single core. Measured by the number of cores, our hosting packages start from 100% (1x CPU core).

PMEM: Physical memory limit (also includes shared memory and disk cache). Measured in GB, our hosting packages start from 1GB.

I/O: It is combines both read & write operations on the hosting server. Measured in MBs per second, our hosting packages start with a limit of 1MB per second.

Entry processes (EP): Usually represents max number of concurrent connections to Apache dynamic scripts as well as  cron jobs running simultaneously. Our basic hosting package start with a limit of 20 entry processes.

Number of process (NPROC): 
Max number of processes within LVE, our hosting accounts start from 100 processes.

Detailed technical information on CloudLinux limits can be found on the Cloudlinux Documentation website.

Errors & Faults - Explained:

You may experience “Resource Limit Reached” error on your website, below are some explanations of some generic error messages.

1 – If the site is limited by CPU or I/O, then the site will start responding slower. No error will be returned to the user. If the number of CPU faults is low (e.g around 100 or less per week), the slowdown may only amount to a mere seconds at the time of the fault.
– If you are only experiencing CPU faults at this rate, this is not a cause for concern.
If the site is limited by memory or number of processes limits, the user will receive 500 or 503 errors that server cannot execute the script.
3 – If the site is limited by Entry Processes, then the user will receive a 508 Resource Limit Reached error.

The most common faults you may encounter are CPU faults and Entry Process faults.

CPU Faults:

CPU faults can be caused by either an internal website process or an external event. CPU faults are often caused by a process which tries to consume more CPU resources than allowed in your hosting package.

Examples of internal website processes which can cause CPU faults:

1– A poorly developed & configured plugin or theme.
2– The website does not cache pages and is not loading pages efficiently.
3– External website software (API Calls) is performing regular website calls to check plugin/theme version and update availability.
4– There is a software installed which crawls (Bots) the website looking for certain content types, for example the Broken Link Checker plugin for WordPress.
5– A lot of processes are being initiated in the backend of the website within a short time frame.
6– Admin activity on a WordPress website cannot be cached, and if activities are happening like Third-Party Plugin Update Checks, you may find CPU resources are used up

Examples of external events which can cause high CPU usage:

1– Brute force attacks.
2– Bot/crawler is visiting the website and there’s no configuration in place to limit bot traffic during visits.
3– A successfully campaign was sent out attracting a influx of visitors within a shorter time period.

Tips to troubleshoot the cause of CPU faults

1- Observe the regularity of the faults, if they are irregular and occurring occasionally, this indicates the CPU faults are caused by an external event such as a brute force attack or a successful newsletter campaign. You can reduce/prevent the impact external events have on your website by optimising the application firewall.

2– You could also verify whether the fault is being caused by attack by first checking the Resource Usage stats in cPanel to identify when the fault(s) occurred, then viewing the website’s access logs during the time the CPU fault(s) occurred.

3– If the faults are occurring regularly at certain intervals or time periods, this indicates an internal website process is not performing efficiently within the allocated resources.

Entry Process (EP) Faults:

When the hosting account exceeds it’s Entry Process resources limits, the server returns a 508 Resource Limit Reached error to prevent a single site from exhausting all web server processes on the server. It’s worth mentioning here that Increased CPU Faults can cause the amount of entry processes to go up as requests cannot be fulfilled as quickly – consequently the website will return a 508 Resource Limit is Reached error until existing requests are processed.

In most cases, exceeding resource limits at low levels is not a cause for concern. If it does become a concern and can’t be solved by troubleshooting and identifying the source of the resource usage, or a higher level of resource usage is required by your website, you can upgrade your hosting subscription to a package which offers further allocations of the resource becoming exhausted.

If you are experiencing CPU Faults or 508 Resource Limit is Reached, although upgrading your hosting package would help process requests faster, you may still continue to experience occasional resource limit faults.

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