PHP - Is there any way to control process executions?

I have php and nodejs installed in my server. I am calling a nodejs code which uses node canvas via php

Like:

<?php 
    exec(node path/to/the/js/file);
?>

Problem:

Each process of this execution consumes around 250 Mb of memory because of node canvas. So If my server has around 8Gb of memory, only 32 users can use the service at any given point of time and also there is a risk of crashing the server if the number of users exceeds.

Is there any scalable solution to this problem?

via Abhinav