Desired State Configuration
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 differently. Since
Ansible 2.4, the win_dsc
module has been added and can be used to take advantage of
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 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 DSCRegistry
resource cannotDSC 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 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 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.
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[]]
)
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
On versions of Ansible older than 2.8, 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.
A [PSCredential]
is defined with EmbeddedInstance("MSFT_Credential")
in
a DSC resource MOF definition.
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: false
Basic: true
Digest: false
Windows: true
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
.
HashTable Type
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 as a
normal dictionary value in YAML. A [HashTable]]
is defined with
EmbeddedInstance("MSFT_KeyValuePair")
in a DSC resource MOF definition.
Arrays
Simple type arrays like [string[]]
or [UInt32[]]
are defined as a list
or as a comma-separated string which is 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.
DateTime
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.
Run As Another User
By default, DSC runs each resource as the SYSTEM account and not the account
that Ansible uses 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, and
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:
# 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
cmdletUsing the
win_psmodule
Ansible moduleSaving the module manually and copying it to another host
The following 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 file path, 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
- name: Extract a zip file
win_dsc:
resource_name: Archive
Destination: C:\temp\output
Path: C:\temp\zip.zip
Ensure: Present
Create a directory
- 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
- 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
- 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: false
Basic: true
Digest: false
Windows: true
See also
- Ansible playbooks
An introduction to playbooks
- Ansible tips and tricks
Tips and tricks for playbooks
- List of Windows Modules
Windows-specific module list, all implemented in PowerShell
- User Mailing List
Have a question? Stop by the Google group!
- Real-time chat
How to join Ansible chat channels