19 KiB
Desired State Configuration
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_NONEproperty type, while the DSCRegistryresource 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 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: TestDataStarting 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[]])
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: PasswordForAdminUserNote
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.
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: yesIn 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 like 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 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
- 3010Complex 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 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: yesCustom 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-Modulecmdlet - Using the
win_psmoduleAnsible 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: presentOnce 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:\tempThis 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: PresentCreate 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: DirectoryInteract 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: yes
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: no
Basic: yes
Digest: no
Windows: yesindex-
The documentation index
playbooks-
An introduction to playbooks
playbooks_best_practices-
Best practices advice
List of Windows Modules <windows_modules>-
Windows specific module list, all implemented in PowerShell
- User Mailing List
-
Have a question? Stop by the google group!
- irc.freenode.net
-
#ansible IRC chat channel