Can IIS configuration be modified concurrently

Question

We have multiple websites in IIS on each of our servers, and we have PowerShell scripts that can create/update an individual website, along with configuring the bindings, SSL, app pools etc.

Given the size of the server farm, and the number of websites, it is highly desirable to be able to upgrade more than one website concurrently.

However, this raises the issue that updates to applicationHost.config of site A, could be overwritten by the concurrent updates for site B.

Is this possible?

Answer 1

Always best to test this:

Lets start with a simple script that create some sites, 20 in this case.

Param
(
    [Parameter(Mandatory=$true)]
    [int]
    $offset
)

Import-Module WebAdministration

ForEach ($number in 1..20 ) {

    $id = $offset + $number
    New-WebSite -Name $("Test_" + $id) -Port $id -Id $id -PhysicalPath "$env:systemdrive\inetpub\wwwroot" 
}

I save this into C:\temp\New-TestSite.ps1

Now run that script three times at the same time, I created another script: C:\temp\Run-Test.ps1 with the following content:

start-job -ScriptBlock {& C:\temp\New-TestSite.ps1 -offset 10000}
start-job -ScriptBlock {& C:\temp\New-TestSite.ps1 -offset 20000}
start-job -ScriptBlock {& C:\temp\New-TestSite.ps1 -offset 30000}

After running Run-Test.ps1, let check how many sites we created:

ls iis:\sites | group {$_.Name.substring(0,6)} | Select Count,Name | Format-Table -AutoSize

I got:

Count Name
----- ----
   19 Test_1
   18 Test_2
   15 Test_3

So we created 52 out of 60

When creating 50 per script, I got:

Count Name
----- ----
   31 Test_1
   31 Test_2
   30 Test_3

that's 92 out of 150

Even worse in some test cases, one of the PowerShell processes crashed:

At least Get-Job shows:

Id     Name            PSJobTypeName   State    
36     Job36           BackgroundJob   Failed   
38     Job38           BackgroundJob   Completed
40     Job40           BackgroundJob   Completed

So in conclusion, we can say it is not save to modify applicationHost.config concurrently.

Of course, this is an extreme test case and doing manual changes concurrently may work, but we should be careful.

Tests ran on Server 2012 R2 (IIS 8.5)