You can limit number of cron jobs, if you use PHP for DevOps software in CentOS 7, which can be easily implemented by checking process by shell_exec.


Below function enables you to check number of process that based on "PHP". 

function count_process($process_name)
{
	// check process in the process list
	$bot_count_cmd = "ps aux | grep \"{$process_name}\" | wc -l";
	$bot_count=shell_exec($bot_count_cmd);
	$bot_count=intval( trim($bot_count) )/2; // you may need to tune the number based on your running environment

	return $bot_count;
}

Note that the working environment above is based on that all the commands are remotely managed and executed by ssh, so all the PHP functions are composed of "bash -c cd..." and the actual php functions like below that is why $bot_count is divided by two.

root      1276  0.0  0.0 113284  1604 ?        Ss   17:45   0:00 bash -c cd "/pub/production/_bot" && php cdn.php
root      1295  1.5  0.1 539480 44648 ?        S    17:45   0:45 php cdn.php
root      2632  0.0  0.0 113284  1600 ?        Ss   17:50   0:00 bash -c cd "/pub/production/_bot" && php cdn.php
root      2651  0.5  0.1 613684 44888 ?        S    17:50   0:13 php cdn.php
root      4062  0.0  0.0 113284  1596 ?        Ss   15:50   0:00 bash -c cd "/pub/production/_bot" && php cdn.php
root      4086  1.0  0.1 539388 46224 ?        D    15:50   1:44 php cdn.php

Below is an application example to run certain function by the number of bots running on the system.

// check cdn.php in the process list
$bot_count=process_count("php cdn.php");

// we will just keep max 5 cdn bots
if (($bot_count)<5) $m_cms->cdn_update( 60*20);

Below is an application example to exit by the number of bots running on the system.

// check encoding.php in the process list
$bot_count=process_count("php encoding.php");

// we will just keep max 2 encoding bots
if (($bot_count)>2) exit;