PM2-Autoscale

PM2 is a module that helps dynamically scale applications based on utilization demand.

Motivation

By default PM2 runs application with specified number of instances which is not suatable when you have few application on one server with many CPUs and you can not predict which application will load your server. For example you have 48 CPUs and if you run application with instances=max PM2 will run 48 instances and every instance usually uses at least 100Mb on the Memory (~5GB for all instances). So if you have 10 application it means you will use about 50GB of the server memory without server load.

Solution

The module helps dynamically increase application instances depends on CPUs utilization of every application. You can run you application with minimum required instances. When module detects that CPU utilisation is higher then scale_cpu_threshold it will start increasing instances to max CPUs-1 and if server has available free memory. When module detects CPU utilization is decreasing it will stop useless instances.

Install

pm2 install pm2-autoscale

Uninstall

pm2 uninstall pm2-autoscale

Configuration

Default settings:

• scale_cpu_threshold Maximum value of CPU utilization one of application instances when the module will try to increase application instances. (default to 30)
• release_cpu_threshold Average value of all CPUs utilization of the application when the module will decrease application instances (default to 5)
• debug Enable debug mode to show logs from the module (default to false)
• max_workers The maximum number of application instances this module will spawn up to (defaults to CPUs-1)
• min_seconds_to_add_worker The minimum number of seconds between spawning new application instances if the load is high CPU utilization is high enough (defaults to 10)
• min_seconds_to_release_worker The minimum number of seconds between closing application instances if the CPU utilization is low enough (defaults to 30)
• average_worker_resources_over_seconds When looking at the CPU and memory utilization of your application instances, this module averages those values out over time, to be less aggressive in spawning new processes, or killing old ones. The lower you set this value, the faster instances are spawned up and killed off (defaults to 60)

To modify the module config values you can use the following commands:

pm2 set pm2-autoscale:debug true
pm2 set pm2-autoscale:scale_cpu_threshold 50