Desired State Configuration =========================== .. contents:: Topics What is Desired State Configuration? ```````````````````````````````````` 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 `_. Host Requirements ````````````````` 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. Why Use DSC? ```````````` 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: * The host does not support PowerShell v5.0, or it cannot easily be upgraded * The DSC resource does not offer a feature present in an Ansible module. For example win_regedit can manage the ``REG_NONE`` property type, while the DSC ``Registry`` resource cannot * DSC resources have limited check mode support, while some Ansible modules have better checks * DSC resources do not support diff mode, while some Ansible modules do * Custom resources require further installation steps to be run on the host beforehand, while Ansible modules are in built-in to Ansible * There are bugs in a DSC resource where an Ansible module works Reasons for using a DSC resource over an Ansible module: * The Ansible module does not support a feature present in a DSC resource * There is no Ansible module available * There are bugs in an existing 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. How to Use DSC? ``````````````` 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 becuase 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 Property Types -------------- 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. PSCredential ++++++++++++ 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:: You should set ``no_log: true`` on the task definition in Ansible to ensure any credentials used are not stored in any log file or console output. CimInstance Type ++++++++++++++++ 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 ``.schema.mof``. Arrays ++++++ 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. Run As Another User ------------------- 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: true Custom DSC Resources ```````````````````` 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. Finding Custom DSC Resources ---------------------------- 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: .. code-block:: powershell # 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. Installing a Custom Resource ---------------------------- There are three ways that a DSC resource can be installed on a host: * Manually with the ``Install-Module`` cmdlet * Using the ``win_psmodule`` Ansible module * Saving the module manually and copying it another host This 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. Examples ```````` Extract a zip file ------------------ .. code-block:: yaml - name: extract a zip file win_dsc: resource_name: Archive Destination: c:\temp\output Path: C:\temp\zip.zip Ensure: Present Create a directory ------------------ .. code-block:: yaml - 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 Interact with Azure ------------------- .. code-block:: yaml - 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: True Ensure: Present Credential_username: '{{ansible_user}}' Credential_password: '{{ansible_password}}' Setup IIS Website ----------------- .. code-block:: yaml - 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 with_items: - Web-Server - Web-Asp-Net45 - name: setup web content win_dsc: resource_name: File DestinationPath: C:\inetpub\IISSite\index.html Type: File Contents: | IIS Site This is the body 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 .. seealso:: :doc:`index` The documentation index :doc:`playbooks` An introduction to playbooks :doc:`playbooks_best_practices` Best practices advice `List of Windows Modules :ref:`` Windows specific module list, all implemented in PowerShell `User Mailing List `_ Have a question? 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