How to retrieve the number of applications associated with a specific IIS AppPool via PowerShell command?
We can see the associated applications manually using:
Get-Item IIS:\AppPools\AppPoolName
However, if we manually want to select the Applications column, it is not possible. Also, the Applications column is not listed within | Get-Member *.
The trick is: PowerShell established so-called "view definition files" which tell PowerShell how to format objects (e.g. whether the object is formatted as a a list or a table, which columns are displayed, etc.). Those files can be found at C:\Windows\System32\WindowsPowerShell\v1.0 and are all ending in .format.ps1xml.
To answer the original question: The file C:\Windows\System32\WindowsPowerShell\v1.0\Modules\WebAdministration\iisprovider.format.ps1xml contains the view definition for the AppPool type which defines a calculated column looking like this:
<TableColumnItem>
<ScriptBlock>
$pn = $_.Name
$sites = get-webconfigurationproperty "/system.applicationHost/sites/site/application[@applicationPool=`'$pn`'and @path='/']/parent::*" machine/webroot/apphost -name name
$apps = get-webconfigurationproperty "/system.applicationHost/sites/site/application[@applicationPool=`'$pn`'and @path!='/']" machine/webroot/apphost -name path
$arr = @()
if ($sites -ne $null) {$arr += $sites}
if ($apps -ne $null) {$arr += $apps}
if ($arr.Length -gt 0) {
$out = ""
foreach ($s in $arr) {$out += $s.Value + "`n"}
$out.Substring(0, $out.Length - 1)
}
</ScriptBlock>
</TableColumnItem>
This answers why the column itself is not a member of the AppPool type. The second question can be easily answered now extracting the necessary code from the "scriptlet" above:
$applicationsInAppPoolCount = @(Get-WebConfigurationProperty `"/system.applicationHost/sites/site/application[@applicationPool=`'$appPool`'and @path!='/']"` "machine/webroot/apphost" -name path).Count