If you need to put load on an Azure VM for testing (like checking if your Azure Monitor Alerts or Autoscale settings are working), using a Perl script is a classic, lightweight way to do it.

Below are three scripts tailored for different types of “stress”: CPU, Memory, and I/O.

1. CPU Load Script

This script performs high-intensity mathematical calculations in a loop to pin the processor.

Perl

#!/usr/bin/perl
# CPU Stress Test
use strict;
use warnings;
print "Starting CPU Load... Press Ctrl+C to stop.\n";
# This will run on one core. 
# To stress multiple cores, run this script multiple times in the background.
while (1) {
    my $x = sqrt(rand(1000000)) * sin(rand(1000000));
}

• Pro Tip: If your VM has 4 cores and you want to hit 100% total CPU, run this 4 times: perl cpu_load.pl & perl cpu_load.pl & perl cpu_load.pl & perl cpu_load.pl &

2. Memory (RAM) Load Script

This script creates a massive string and keeps adding to it to consume available RAM. Warning: Be careful with this; if it consumes all RAM, the Linux OOM (Out of Memory) killer might crash the VM.

Perl

#!/usr/bin/perl
# Memory Stress Test
use strict;
use warnings;
print "How many MB of RAM should I consume? ";
my $mb_to_hit = <STDIN>;
chomp($mb_to_hit);
my $data = "";
my $chunk = "A" x (1024 * 1024); # 1MB string chunk
print "Allocating memory...\n";
for (1..$mb_to_hit) {
    $data .= $chunk;
    print "Currently holding approx $_ MB\n" if $_ % 100 == 0;
}
print "Memory allocated. Press Enter to release memory and exit.";
<STDIN>;

3. I/O (Disk) Load Script

This script continuously writes and deletes a file to stress the Virtual Machine’s disk IOPS (Input/Output Operations Per Second).

Perl

#!/usr/bin/perl
# Disk I/O Stress Test
use strict;
use warnings;
my $filename = "test_load_file.tmp";
print "Starting Disk I/O load... Press Ctrl+C to stop.\n";
while (1) {
    open(my $fh, '>', $filename) or die "Could not open file: $!";
    print $fh "This is a stress test line\n" x 10000;
    close $fh;
    unlink($filename); # Deletes the file immediately to repeat the write
}

💡 The “Cloud Native” Alternative: stress-ng

While Perl scripts are great, most Azure Engineers use a tool called stress-ng. It is purpose-built for this and gives you much more granular control over exactly how many cores or how much RAM you hit.

To install and run (Ubuntu/Debian):

Bash

sudo apt update && sudo apt install stress-ng -y
# Stress 2 CPUs for 60 seconds
stress-ng --cpu 2 --timeout 60s
# Stress 1GB of RAM
stress-ng --vm 1 --vm-bytes 1G --timeout 60s

🛑 Important Reminder

When putting load on a VM, keep a separate window open with the command top or htop (if installed) to monitor the resource usage in real-time. If you are testing Azure Autoscale, remember that it usually takes 5–10 minutes for the Azure portal to reflect the spike and trigger the scaling action!