Desired State Configuration, or DSC, is a tool built into PowerShell that can be used to define a Windows host setup through code. The overall purpose of DSC is the same as Ansible, it is just executed in a different manner. Since Ansible 2.4, the win_dsc module has been added and can be used to leverage existing DSC resources when interacting with a Windows host.
More details on DSC can be viewed at DSC Overview.
To use the win_dsc module, a Windows host must have PowerShell v5.0 or newer installed. All supported hosts, except for Windows Server 2008 (non R2) can be upgraded to PowerShell v5.
Once the PowerShell requirements have been met, using DSC is as simple as creating a task with the win_dsc module.
DSC and Ansible modules have a common goal which is to define and ensure the state of a resource. Because of this, resources like the DSC File resource and Ansible win_file can be used to achieve the same result. Deciding which to use depends on the scenario.
Reasons for using an Ansible module over a DSC resource:
REG_NONE property type, while the DSC Registry resource cannotReasons for using a DSC resource over an Ansible module:
In the end, it doesn’t matter whether the task is performed with DSC or an Ansible module; what matters is that the task is performed correctly and the playbooks are still readable. If you have more experience with DSC over Ansible and it does the job, just use DSC for that task.
The win_dsc module takes in a free-form of options so that it changes according to the resource it is managing. A list of built in resources can be found at resources.
Using the Registry resource as an example, this is the DSC definition as documented by Microsoft:
Registry [string] #ResourceName
{
Key = [string]
ValueName = [string]
[ Ensure = [string] { Enable | Disable } ]
[ Force = [bool] ]
[ Hex = [bool] ]
[ DependsOn = [string[]] ]
[ ValueData = [string[]] ]
[ ValueType = [string] { Binary | Dword | ExpandString | MultiString | Qword | String } ]
}
When defining the task, resource_name must be set to the DSC resource being used - in this case the resource_name should be set to Registry. The module_version can refer to a specific version of the DSC resource installed; if left blank it will default to the latest version. The other options are parameters that are used to define the resource, such as Key and ValueName. While the options in the task are not case sensitive, keeping the case as-is is recommended because it makes it easier to distinguish DSC resource options from Ansible’s win_dsc options.
This is what the Ansible task version of the above DSC Registry resource would look like:
- name: Use win_dsc module with the Registry DSC resource
win_dsc:
resource_name: Registry
Ensure: Present
Key: HKEY_LOCAL_MACHINE\SOFTWARE\ExampleKey
ValueName: TestValue
ValueData: TestData
Starting in Ansible 2.8, the win_dsc module automatically validates the input options from Ansible with the DSC definition. This means Ansible will fail if the option name is incorrect, a mandatory option is not set, or the value is not a valid choice. When running Ansible with a verbosity level of 3 or more (-vvv), the return value will contain the possible invocation options based on the resource_name specified. Here is an example of the invocation output for the above Registry task:
changed: [2016] => {
"changed": true,
"invocation": {
"module_args": {
"DependsOn": null,
"Ensure": "Present",
"Force": null,
"Hex": null,
"Key": "HKEY_LOCAL_MACHINE\\SOFTWARE\\ExampleKey",
"PsDscRunAsCredential_password": null,
"PsDscRunAsCredential_username": null,
"ValueData": [
"TestData"
],
"ValueName": "TestValue",
"ValueType": null,
"module_version": "latest",
"resource_name": "Registry"
}
},
"module_version": "1.1",
"reboot_required": false,
"verbose_set": [
"Perform operation 'Invoke CimMethod' with following parameters, ''methodName' = ResourceSet,'className' = MSFT_DSCLocalConfigurationManager,'namespaceName' = root/Microsoft/Windows/DesiredStateConfiguration'.",
"An LCM method call arrived from computer SERVER2016 with user sid S-1-5-21-3088887838-4058132883-1884671576-1105.",
"[SERVER2016]: LCM: [ Start Set ] [[Registry]DirectResourceAccess]",
"[SERVER2016]: [[Registry]DirectResourceAccess] (SET) Create registry key 'HKLM:\\SOFTWARE\\ExampleKey'",
"[SERVER2016]: [[Registry]DirectResourceAccess] (SET) Set registry key value 'HKLM:\\SOFTWARE\\ExampleKey\\TestValue' to 'TestData' of type 'String'",
"[SERVER2016]: LCM: [ End Set ] [[Registry]DirectResourceAccess] in 0.1930 seconds.",
"[SERVER2016]: LCM: [ End Set ] in 0.2720 seconds.",
"Operation 'Invoke CimMethod' complete.",
"Time taken for configuration job to complete is 0.402 seconds"
],
"verbose_test": [
"Perform operation 'Invoke CimMethod' with following parameters, ''methodName' = ResourceTest,'className' = MSFT_DSCLocalConfigurationManager,'namespaceName' = root/Microsoft/Windows/DesiredStateConfiguration'.",
"An LCM method call arrived from computer SERVER2016 with user sid S-1-5-21-3088887838-4058132883-1884671576-1105.",
"[SERVER2016]: LCM: [ Start Test ] [[Registry]DirectResourceAccess]",
"[SERVER2016]: [[Registry]DirectResourceAccess] Registry key 'HKLM:\\SOFTWARE\\ExampleKey' does not exist",
"[SERVER2016]: LCM: [ End Test ] [[Registry]DirectResourceAccess] False in 0.2510 seconds.",
"[SERVER2016]: LCM: [ End Set ] in 0.3310 seconds.",
"Operation 'Invoke CimMethod' complete.",
"Time taken for configuration job to complete is 0.475 seconds"
]
}
The invocation.module_args key shows the actual values that were set as well as other possible values that were not set. Unfortunately this will not show the default value for a DSC property, only what was set from the Ansible task. Any *_password option will be masked in the output for security reasons, if there are any other sensitive module options, set no_log: True on the task to stop all task output from being logged.
Each DSC resource property has a type that is associated with it. Ansible will try to convert the defined options to the correct type during execution. For simple types like [string] and [bool] this is a simple operation, but complex types like [PSCredential] or arrays (like [string[]]) this require certain rules.
A [PSCredential] object is used to store credentials in a secure way, but Ansible has no way to serialize this over JSON. To set a DSC PSCredential property, the definition of that parameter should have two entries that are suffixed with _username and _password for the username and password respectively. For example:
PsDscRunAsCredential_username: '{{ ansible_user }}'
PsDscRunAsCredential_password: '{{ ansible_password }}'
SourceCredential_username: AdminUser
SourceCredential_password: PasswordForAdminUser
Note
On versions of Ansible older than 2.8, you should set no_log: yes on the task definition in Ansible to ensure any credentials used are not stored in any log file or console output.
A [PSCredential] is defined with EmbeddedInstance("MSFT_Credential") in a DSC resource MOF definition.
A [CimInstance] object is used by DSC to store a dictionary object based on a custom class defined by that resource. Defining a value that takes in a [CimInstance] in YAML is the same as defining a dictionary in YAML. For example, to define a [CimInstance] value in Ansible:
# [CimInstance]AuthenticationInfo == MSFT_xWebAuthenticationInformation AuthenticationInfo: Anonymous: no Basic: yes Digest: no Windows: yes
In the above example, the CIM instance is a representation of the class MSFT_xWebAuthenticationInformation. This class accepts four boolean variables, Anonymous, Basic, Digest, and Windows. The keys to use in a [CimInstance] depend on the class it represents. Please read through the documentation of the resource to determine the keys that can be used and the types of each key value. The class definition is typically located in the <resource name>.schema.mof.
A [HashTable] object is also a dictionary but does not have a strict set of keys that can/need to be defined. Like a [CimInstance], define it like a normal dictionary value in YAML. A [HashTable]] is defined with EmbeddedInstance("MSFT_KeyValuePair") in a DSC resource MOF definition.
Simple type arrays like [string[]] or [UInt32[]] are defined as a list or as a comma separated string which are then cast to their type. Using a list is recommended because the values are not manually parsed by the win_dsc module before being passed to the DSC engine. For example, to define a simple type array in Ansible:
# [string[]] ValueData: entry1, entry2, entry3 ValueData: - entry1 - entry2 - entry3 # [UInt32[]] ReturnCode: 0,3010 ReturnCode: - 0 - 3010
Complex type arrays like [CimInstance[]] (array of dicts), can be defined like this example:
# [CimInstance[]]BindingInfo == MSFT_xWebBindingInformation BindingInfo: - Protocol: https Port: 443 CertificateStoreName: My CertificateThumbprint: C676A89018C4D5902353545343634F35E6B3A659 HostName: DSCTest IPAddress: '*' SSLFlags: 1 - Protocol: http Port: 80 IPAddress: '*'
The above example, is an array with two values of the class MSFT_xWebBindingInformation. When defining a [CimInstance[]], be sure to read the resource documentation to find out what keys to use in the definition.
A [DateTime] object is a DateTime string representing the date and time in the ISO 8601 date time format. The value for a [DateTime] field should be quoted in YAML to ensure the string is properly serialized to the Windows host. Here is an example of how to define a [DateTime] value in Ansible:
# As UTC-0 (No timezone) DateTime: '2019-02-22T13:57:31.2311892+00:00' # As UTC+4 DateTime: '2019-02-22T17:57:31.2311892+04:00' # As UTC-4 DateTime: '2019-02-22T09:57:31.2311892-04:00'
All the values above are equal to a UTC date time of February 22nd 2019 at 1:57pm with 31 seconds and 2311892 milliseconds.
By default, DSC runs each resource as the SYSTEM account and not the account that Ansible use to run the module. This means that resources that are dynamically loaded based on a user profile, like the HKEY_CURRENT_USER registry hive, will be loaded under the SYSTEM profile. The parameter PsDscRunAsCredential is a parameter that can be set for every DSC resource force the DSC engine to run under a different account. As PsDscRunAsCredential has a type of PSCredential, it is defined with the _username and _password suffix.
Using the Registry resource type as an example, this is how to define a task to access the HKEY_CURRENT_USER hive of the Ansible user:
- name: Use win_dsc with PsDscRunAsCredential to run as a different user
win_dsc:
resource_name: Registry
Ensure: Present
Key: HKEY_CURRENT_USER\ExampleKey
ValueName: TestValue
ValueData: TestData
PsDscRunAsCredential_username: '{{ ansible_user }}'
PsDscRunAsCredential_password: '{{ ansible_password }}'
no_log: yes
DSC resources are not limited to the built-in options from Microsoft. Custom modules can be installed to manage other resources that are not usually available.
You can use the PSGallery to find custom resources, along with documentation on how to install them on a Windows host.
The Find-DscResource cmdlet can also be used to find custom resources. For example:
# Find all DSC resources in the configured repositories Find-DscResource # Find all DSC resources that relate to SQL Find-DscResource -ModuleName "*sql*"
Note
DSC resources developed by Microsoft that start with x, means the resource is experimental and comes with no support.
There are three ways that a DSC resource can be installed on a host:
Install-Module cmdletwin_psmodule Ansible moduleThis is an example of installing the xWebAdministration resources using win_psmodule:
- name: Install xWebAdministration DSC resource
win_psmodule:
name: xWebAdministration
state: present
Once installed, the win_dsc module will be able to use the resource by referencing it with the resource_name option.
The first two methods above only work when the host has access to the internet. When a host does not have internet access, the module must first be installed using the methods above on another host with internet access and then copied across. To save a module to a local filepath, the following PowerShell cmdlet can be run:
Save-Module -Name xWebAdministration -Path C:\temp
This will create a folder called xWebAdministration in C:\temp which can be copied to any host. For PowerShell to see this offline resource, it must be copied to a directory set in the PSModulePath environment variable. In most cases the path C:\Program Files\WindowsPowerShell\Module is set through this variable, but the win_path module can be used to add different paths.
- name: Extract a zip file
win_dsc:
resource_name: Archive
Destination: C:\temp\output
Path: C:\temp\zip.zip
Ensure: Present
- name: Create file with some text
win_dsc:
resource_name: File
DestinationPath: C:\temp\file
Contents: |
Hello
World
Ensure: Present
Type: File
- name: Create directory that is hidden is set with the System attribute
win_dsc:
resource_name: File
DestinationPath: C:\temp\hidden-directory
Attributes: Hidden,System
Ensure: Present
Type: Directory
- name: Install xAzure DSC resources
win_psmodule:
name: xAzure
state: present
- name: Create virtual machine in Azure
win_dsc:
resource_name: xAzureVM
ImageName: a699494373c04fc0bc8f2bb1389d6106__Windows-Server-2012-R2-201409.01-en.us-127GB.vhd
Name: DSCHOST01
ServiceName: ServiceName
StorageAccountName: StorageAccountName
InstanceSize: Medium
Windows: yes
Ensure: Present
Credential_username: '{{ ansible_user }}'
Credential_password: '{{ ansible_password }}'
- name: Install xWebAdministration module
win_psmodule:
name: xWebAdministration
state: present
- name: Install IIS features that are required
win_dsc:
resource_name: WindowsFeature
Name: '{{ item }}'
Ensure: Present
loop:
- Web-Server
- Web-Asp-Net45
- name: Setup web content
win_dsc:
resource_name: File
DestinationPath: C:\inetpub\IISSite\index.html
Type: File
Contents: |
<html>
<head><title>IIS Site</title></head>
<body>This is the body</body>
</html>
Ensure: present
- name: Create new website
win_dsc:
resource_name: xWebsite
Name: NewIISSite
State: Started
PhysicalPath: C:\inetpub\IISSite\index.html
BindingInfo:
- Protocol: https
Port: 8443
CertificateStoreName: My
CertificateThumbprint: C676A89018C4D5902353545343634F35E6B3A659
HostName: DSCTest
IPAddress: '*'
SSLFlags: 1
- Protocol: http
Port: 8080
IPAddress: '*'
AuthenticationInfo:
Anonymous: no
Basic: yes
Digest: no
Windows: yes
See also
© 2012–2018 Michael DeHaan
© 2018–2019 Red Hat, Inc.
Licensed under the GNU General Public License version 3.
https://docs.ansible.com/ansible/2.9/user_guide/windows_dsc.html