Get-Test-Set
Applies To: Windows PowerShell 4.0, Windows PowerShell 5.0
PowerShell Desired State Configuration is constructed around a Get, Test, and Set process. DSC resources each contains methods to complete each of these operations. In a Configuration, you define resource blocks to fill in keys that become parameters for a resource's Get, Test, and Set methods.
This is the syntax for a Service resource block. The Service resource configures Windows services.
Service [String] #ResourceName
{
Name = [string]
[BuiltInAccount = [string]{ LocalService | LocalSystem | NetworkService }]
[Credential = [PSCredential]]
[Dependencies = [string[]]]
[DependsOn = [string[]]]
[Description = [string]]
[DisplayName = [string]]
[Ensure = [string]{ Absent | Present }]
[Path = [string]]
[PsDscRunAsCredential = [PSCredential]]
[StartupType = [string]{ Automatic | Disabled | Manual }]
[State = [string]{ Running | Stopped }]
}
The Get, Test, and Set methods of the Service resource will have parameter blocks that accept these values.
param
(
[parameter(Mandatory = $true)]
[ValidateNotNullOrEmpty()]
[System.String]
$Name,
[System.String]
[ValidateSet("Automatic", "Manual", "Disabled")]
$StartupType,
[System.String]
[ValidateSet("LocalSystem", "LocalService", "NetworkService")]
$BuiltInAccount,
[System.Management.Automation.PSCredential]
[ValidateNotNull()]
$Credential,
[System.String]
[ValidateSet("Running", "Stopped")]
$State="Running",
[System.String]
[ValidateNotNullOrEmpty()]
$DisplayName,
[System.String]
[ValidateNotNullOrEmpty()]
$Description,
[System.String]
[ValidateNotNullOrEmpty()]
$Path,
[System.String[]]
[ValidateNotNullOrEmpty()]
$Dependencies,
[System.String]
[ValidateSet("Present", "Absent")]
$Ensure="Present"
)
Note
The language and method used to define the resource determines how the Get, Test, and Set methods will be defined.
Because the Service resource only has one required key (Name), a Service block resource
could be as simple as this:
Configuration TestConfig
{
Import-DSCResource -Name Service
Node localhost
{
Service "MyService"
{
Name = "Spooler"
}
}
}
When you compile the Configuration above, the values you specify for a key are stored in the .mof
file that is generated. For more information, see MOF.
instance of MSFT_ServiceResource as $MSFT_ServiceResource1ref
{
SourceInfo = "::5::1::Service";
ModuleName = "PsDesiredStateConfiguration";
ResourceID = "[Service]MyService";
Name = "Spooler";
ModuleVersion = "1.0";
ConfigurationName = "Test";
};
When applied, the Local Configuration Manager (LCM) will read the
value "Spooler" from the .mof file, and pass it to the Name parameter of the Get,
Test, and Set methods for the "MyService" instance of the Service resource.
Get
The Get method of a resource, retrieves the state of the resource as it is configured on the target Node. This state is returned as a hashtable. The keys of the hashtable will be the configurable values, or parameters, the resource accepts.
The Get method maps directly to the
Get-DSCConfiguration cmdlet.
When you call Get-DSCConfiguration, the LCM runs the Get method of each resource in the
currently applied configuration. The LCM uses the key values stored in the .mof file as parameters
to each corresponding resource instance.
This is sample output from a Service resource that configures the "Spooler" service.
ConfigurationName : Test
DependsOn :
ModuleName : PsDesiredStateConfiguration
ModuleVersion : 1.1
PsDscRunAsCredential :
ResourceId : [Service]Spooler
SourceInfo :
BuiltInAccount : LocalSystem
Credential :
Dependencies : {RPCSS, http}
Description : This service spools print jobs and handles interaction with the printer. If you turn off
this service, you won't be able to print or see your printers.
DisplayName : Print Spooler
Ensure :
Name : Spooler
Path : C:\WINDOWS\System32\spoolsv.exe
StartupType : Automatic
State : Running
Status :
PSComputerName :
CimClassName : MSFT_ServiceResource
The output shows the current value properties configurable by the Service resource.
Service [String] #ResourceName
{
Name = [string]
[BuiltInAccount = [string]{ LocalService | LocalSystem | NetworkService }]
[Credential = [PSCredential]]
[Dependencies = [string[]]]
[DependsOn = [string[]]]
[Description = [string]]
[DisplayName = [string]]
[Ensure = [string]{ Absent | Present }]
[Path = [string]]
[PsDscRunAsCredential = [PSCredential]]
[StartupType = [string]{ Automatic | Disabled | Manual }]
[State = [string]{ Running | Stopped }]
}
Test
The Test method of a resource determines if the target node is currently compliant with the
resource's desired state. The Test method returns $true or $false only to indicate whether
the Node is compliant. When you call
Test-DSCConfiguration, the
LCM calls the Test method of each resource in the currently applied configuration. The LCM uses
the key values stored in the ".mof" file as parameters to each corresponding resource instance.
If the result of any individual resource's Test is $false, Test-DSCConfiguration returns
$false indicating that the Node is not compliant. If all resource's Test methods return
$true, Test-DSCConfiguration returns $true to indicate that the Node is compliant.
Test-DSCConfiguration
True
Beginning in PowerShell 5.0, the Detailed parameter was added. Specifying Detailed causes
Test-DSCConfiguration to return an object containing collections of results for compliant, and
non-compliant resources.
Test-DSCConfiguration -Detailed
PSComputerName ResourcesInDesiredState ResourcesNotInDesiredState InDesiredState
-------------- ----------------------- -------------------------- --------------
localhost {[Service]Spooler} True
For more information, see Test-DSCConfiguration.
Set
The Set method of a resource attempts to force the Node to become compliant with the resource's
desired state. The Set method is meant to be idempotent, which means that Set could be
run multiple times and always get the same result without errors. When you run
Start-DSCConfiguration, the
LCM cycles through each resource in the currently applied configuration. The LCM retrieves key
values for the current resource instance from the ".mof" file and uses them as parameters for the
Test method. If the Test method returns $true, the Node is compliant with the current
resource, and the Set method is skipped. If the Test returns $false, the Node is
non-compliant. The LCM passes the resource instance's key values as parameters to the resource's
Set method, restoring the Node to compliance.
By specifying the Verbose and Wait parameters, you can watch the progress of the
Start-DSCConfiguration cmdlet. In this example, the Node is already compliant. The Verbose
output indicates that the Set method was skipped.
PS> Start-DSCConfiguration -Verbose -Wait -UseExisting
VERBOSE: Perform operation 'Invoke CimMethod' with following parameters, ''methodName' =
ApplyConfiguration,'className' = MSFT_DSCLocalConfigurationManager,'namespaceName' =
root/Microsoft/Windows/DesiredStateConfiguration'.
VERBOSE: An LCM method call arrived from computer SERVER01 with user sid
S-1-5-21-124525095-708259637-1543119021-1282804.
VERBOSE: [SERVER01]: [] Starting consistency engine.
VERBOSE: [SERVER01]: [] Checking consistency for current configuration.
VERBOSE: [SERVER01]: [DSCEngine] Importing the module
C:\WINDOWS\system32\WindowsPowerShell\v1.0\Modules\PSDesiredStateConfiguration\DscResources\MSFT_ServiceResource\MSFT
_ServiceResource.psm1 in force mode.
VERBOSE: [SERVER01]: LCM: [ Start Resource ] [[Service]Spooler]
VERBOSE: [SERVER01]: LCM: [ Start Test ] [[Service]Spooler]
VERBOSE: [SERVER01]: [[Service]Spooler] Importing the module MSFT_ServiceResource in
force mode.
VERBOSE: [SERVER01]: LCM: [ End Test ] [[Service]Spooler] in 0.2540 seconds.
VERBOSE: [SERVER01]: LCM: [ Skip Set ] [[Service]Spooler]
VERBOSE: [SERVER01]: LCM: [ End Resource ] [[Service]Spooler]
VERBOSE: [SERVER01]: [] Consistency check completed.
VERBOSE: Operation 'Invoke CimMethod' complete.
VERBOSE: Time taken for configuration job to complete is 1.379 seconds
