29.19 Invoke a Command on Many Computers

Problem

You want to manage many computers simultaneously.

Solution

Use the -ThrottleLimit and -AsJob parameters to configure how PowerShell scales out your commands:

PS > $sessions = $(
    New-PSSession localhost;
    New-PSSession localhost;
    New-PSSession localhost)

PS > $start = Get-Date
PS > Invoke-Command $sessions { Start-Sleep 2; "Test $pid" }
Test 720
Test 6112
Test 4792
PS > (Get-Date) - $start | Select TotalSeconds | Format-Table -Auto

TotalSeconds
------------
     2.09375


PS >
PS > $start = Get-Date
PS > Invoke-Command $sessions { Start-Sleep 2; "Test $pid" } -ThrottleLimit 1
Test 6112
Test 4792
Test 720
PS > (Get-Date) - $start | Select TotalSeconds | Format-Table -Auto

TotalSeconds
------------
        6.25

Discussion

One of the largest difficulties in traditional networking scripts comes from managing many computers at once. Remote computer management is typically network-bound, so most scripts spend the majority of their time waiting for the network.

The solution to this is to scale. Rather than manage one computer at a time, you manage several. Not too many, however, as few machines can handle the demands of connecting to hundreds or thousands of remote machines at once.

Despite the benefits, writing a networking script that supports smart automatic throttling is beyond the capability of many and too far down “the big list of things to do” of most. Fortunately, PowerShell Remoting’s main focus is to solve these common problems, and throttling is no exception.

By default, PowerShell Remoting connects to 32 computers at a time. After running your command on the first 32 computers in your list, it waits for commands to complete before running your command on additional computers. As each command completes, PowerShell invokes the next one waiting.

To demonstrate this automatic scaling, the Solution shows the difference between calling Invoke-Command with the default throttle limit and calling it with a throttle limit of one computer.

When working against many computers at a time, you might want to continue using your shell while these long-running tasks process in the background. To support background processing of tasks, the Invoke-Command cmdlet offers -AsJob, which lets you run your command as a PowerShell Job.

For more information about PowerShell Jobs, see Recipe 1.6.

See Also

Recipe 1.6, “Invoke a Long-Running or Background Command”

Recipe 29.5, “Invoke a Command on a Remote Computer”