How to run a PowerShell script as a Windows service

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Brandon Olin

Brandon is a Cloud Architect and veteran Systems Engineer with a penchant for PowerShell, DevOps processes, and open-source software. You can reach Brandon at devblackops.io or on Twitter @devblackops.

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The scenario

Most PowerShell scripts aim to run a task and then exit. You'll usually execute a script from the PowerShell console or perhaps trigger it periodically via the Windows Task Scheduler. However, you may want to run a script 24/7 and ensure it starts up again after a reboot or crash. To do this, the easiest option is to use NSSM.

About NSSM

If you've not heard about NSSM before, it's a small service helper similar to the built-in program srvany. NSSM aims to make it extremely simple to configure any binary to run as a service and ensure it stays running. You can take a look at the NSSM website for more information about common use cases.

Example script

Take this example script below. This script runs a small web server using the Polaris framework. Polaris is a cross-platform, minimalist web framework written in PowerShell. Currently, this is not a Microsoft-supported module, but I encourage you to look at it if you are interested in experimenting with web servers and PowerShell commands. Like a normal web server, ours should run all the time, and we will use a Windows service to achieve this.

[cmdletbinding()]
param()

Import-Module -Name Polaris

New-PolarisGetRoute -Path '/helloworld' -Scriptblock {
    $Response.Send('Hello World!')
}

Start-Polaris -Port 8080

while($true) {
    Start-Sleep -Milliseconds 10
}

Installing Polaris

Currently, Polaris is not available in the PowerShell Gallery, so we'll need to install it manually. Download the zip archive from the git repository, and extract the contents to C:\Program Files\WindowsPowerShell\Modules\Polaris.

Download the Polaris zip file

Your modules directory should look like this:

Polaris extracted to the modules folder

If we run this script manually, we can verify Polaris is running and serving requests at http://localhost:8080/helloworld. It will keep running until you press Ctrl+C.

Starting Polaris

Testing Polaris in the browser

Install NSSM

Now on to installing NSSM so we can configure our Windows service. If you are already using Chocolatey, you can install NSSM with the following:

Installing NSSM with Chocolatey

If you don't have Chocolatey installed, you can download NSSM here.

Install the Windows service

After installing NSSM, we'll need to run a few commands to install our web server script as a Windows service. You'll need to run these next commands as an administrator.

We have to define a few variables. We'll need the path to NSSM itself, the name of the service we want to create, the path to PowerShell, the path to our Polaris script, and the argument string we'll pass to PowerShell.

$nssm = (Get-Command nssm).Source
$serviceName = 'Polaris'
$powershell = (Get-Command powershell).Source
$scriptPath = 'C:/4sysops/Start-Polaris.ps1'
$arguments = '-ExecutionPolicy Bypass -NoProfile -File "{0}"' -f $scriptPath
& $nssm install $serviceName $powershell $arguments
& $nssm status $serviceName
Start-Service $serviceName
Get-Service $serviceName

Install a script as a service

Validating the script

Now that we've installed our new service, we can test everything is working with Invoke-RestMethod.

Testing the web server with Invoke RestMethod

As with any Windows service, we can also set this to start automatically on boot or restart if it unexpectedly terminates.

Conclusion

You might find running a PowerShell script as a service handy in many use cases. Hopefully I've just whetted your appetite on what you can do with services, NSSM, and PowerShell.