dsc_resource Resource

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Windows PowerShell is a task-based command-line shell and scripting language developed by Microsoft. Windows PowerShell uses a document-oriented approach for managing Windows-based machines, similar to the approach that is used for managing Unix and Linux-based machines. Windows PowerShell is a tool-agnostic platform that supports using Chef for configuration management.

Desired State Configuration (DSC) is a feature of Windows PowerShell that provides a set of language extensions, cmdlets, and resources that can be used to declaratively configure software. DSC is similar to Chef, in that both tools are idempotent, take similar approaches to the concept of resources, describe the configuration of a system, and then take the steps required to do that configuration. The most important difference between Chef and DSC is that Chef uses Ruby and DSC is exposed as configuration data from within Windows PowerShell.

The dsc_resource resource allows any DSC resource to be used in a Chef recipe, as well as any custom resources that have been added to your Windows PowerShell environment. Microsoft frequently adds new resources to the DSC resource collection.

Syntax

A dsc_resource resource block allows DSC resources to be used in a Chef recipe. For example, the DSC Archive resource:

Archive ExampleArchive {
  Ensure = "Present"
  Path = "C:\Users\Public\Documents\example.zip"
  Destination = "C:\Users\Public\Documents\ExtractionPath"
}

and then the same dsc_resource with Chef:

dsc_resource 'example' do
   resource :archive
   property :ensure, 'Present'
   property :path, "C:\Users\Public\Documents\example.zip"
   property :destination, "C:\Users\Public\Documents\ExtractionPath"
 end```

The full syntax for all of the properties that are available to the dsc_resource resource is:

dsc_resource 'name' do
  module_name                String
  module_version             String
  property                   Symbol
  reboot_action              Symbol # default value: :nothing
  resource                   Symbol
  timeout                    Integer
  action                     Symbol # defaults to :run if not specified
end

where:

• dsc_resource is the resource.
• name is the name given to the resource block.
• action identifies which steps Chef Infra Client will take to bring the node into the desired state.
• property is zero (or more) properties in the DSC resource, where each property is entered on a separate line, :dsc_property_name is the case-insensitive name of that property, and "property_value" is a Ruby value to be applied by Chef Infra Client
• module_name, module_version, property, reboot_action, resource, and timeout are properties of this resource, with the Ruby type shown. See “Properties” section below for more information about all of the properties that may be used with this resource.

Actions

The dsc_resource resource has the following actions:

:nothing

This resource block does not act unless notified by another resource to take action. Once notified, this resource block either runs immediately or is queued up to run at the end of a Chef Infra Client run.

:run

Default. Use to run the DSC configuration defined as defined in this resource.

Properties

The dsc_resource resource has the following properties:

module_name

Ruby Type: String

The name of the module from which a DSC resource originates. If this property is not specified, it will be inferred.

module_version

Ruby Type: String

The version number of the module to use. PowerShell 5.0.10018.0 (or higher) supports having multiple versions of a module installed. This should be specified along with the module_name.

New in Chef Client 12.21

property

Ruby Type: Symbol

A property from a Desired State Configuration (DSC) resource. Use this property multiple times, one for each property in the Desired State Configuration (DSC) resource. The format for this property must follow property :dsc_property_name, "property_value" for each DSC property added to the resource block.

The :dsc_property_name must be a symbol.

Use the following Ruby types to define property_value:

Ruby	Windows PowerShell
Array	Object[]
Chef::Util::Powershell:PSCredential	PSCredential
False	bool($false)
Fixnum	Integer
Float	Double
Hash	Hashtable
True	bool($true)

These are converted into the corresponding Windows PowerShell type during a Chef Infra Client run.

reboot_action

Ruby Type: Symbol | Default Value: :nothing
Allowed Values: :nothing, :reboot_now, :request_reboot

Use to request an immediate reboot or to queue a reboot using the :reboot_now (immediate reboot) or :request_reboot (queued reboot) actions built into the reboot resource.

New in Chef Client 12.6

resource

Ruby Type: Symbol

The name of the DSC resource. This value is case-insensitive and must be a symbol that matches the name of the DSC resource.

For built-in DSC resources, use the following values:

Value	Description
:archive	Use to unpack archive (.zip) files.
:environment	Use to manage system environment variables.
:file	Use to manage files and directories.
:group	Use to manage local groups.
:log	Use to log configuration messages.
:package	Use to install and manage packages.
:registry	Use to manage registry keys and registry key values.
:script	Use to run PowerShell script blocks.
:service	Use to manage services.
:user	Use to manage local user accounts.
:windowsfeature	Use to add or remove Windows features and roles.
:windowsoptionalfeature	Use to configure Microsoft Windows optional features.
:windowsprocess	Use to configure Windows processes.

Any DSC resource may be used in a Chef recipe. For example, the DSC Resource Kit contains resources for configuring Active Directory components, such as xADDomain, xADDomainController, and xADUser. Assuming that these resources are available to Chef Infra Client, the corresponding values for the resource attribute would be: :xADDomain, :xADDomainController, and xADUser.

timeout

Ruby Type: Integer

The amount of time (in seconds) a command is to wait before timing out.

Common Resource Functionality

Chef resources include common properties, notifications, and resource guards.

Common Properties

The following properties are common to every resource:

compile_time

Ruby Type: true, false | Default Value: false

Control the phase during which the resource is run on the node. Set to true to run while the resource collection is being built (the compile phase). Set to false to run while Chef Infra Client is configuring the node (the converge phase).

ignore_failure

Ruby Type: true, false, :quiet | Default Value: false

Continue running a recipe if a resource fails for any reason. :quiet will not display the full stack trace and the recipe will continue to run if a resource fails.

retries

Ruby Type: Integer | Default Value: 0

The number of attempts to catch exceptions and retry the resource.

retry_delay

Ruby Type: Integer | Default Value: 2

The delay in seconds between retry attempts.

sensitive

Ruby Type: true, false | Default Value: false

Ensure that sensitive resource data is not logged by Chef Infra Client.

Notifications

notifies

Ruby Type: Symbol, 'Chef::Resource[String]'

A resource may notify another resource to take action when its state changes. Specify a 'resource[name]', the :action that resource should take, and then the :timer for that action. A resource may notify more than one resource; use a notifies statement for each resource to be notified.

If the referenced resource does not exist, an error is raised. In contrast, subscribes will not fail if the source resource is not found.

A timer specifies the point during a Chef Infra Client run at which a notification is run. The following timers are available:

:before

Specifies that the action on a notified resource should be run before processing the resource block in which the notification is located.

:delayed

Default. Specifies that a notification should be queued up, and then executed at the end of a Chef Infra Client run.

:immediate, :immediately

Specifies that a notification should be run immediately, for each resource notified.

The syntax for notifies is:

notifies :action, 'resource[name]', :timer

subscribes

Ruby Type: Symbol, 'Chef::Resource[String]'

A resource may listen to another resource, and then take action if the state of the resource being listened to changes. Specify a 'resource[name]', the :action to be taken, and then the :timer for that action.

Note that subscribes does not apply the specified action to the resource that it listens to - for example:

file '/etc/nginx/ssl/example.crt' do
  mode '0600'
  owner 'root'
end

service 'nginx' do
  subscribes :reload, 'file[/etc/nginx/ssl/example.crt]', :immediately
end

In this case the subscribes property reloads the nginx service whenever its certificate file, located under /etc/nginx/ssl/example.crt, is updated. subscribes does not make any changes to the certificate file itself, it merely listens for a change to the file, and executes the :reload action for its resource (in this example nginx) when a change is detected.

If the other resource does not exist, the subscription will not raise an error. Contrast this with the stricter semantics of notifies, which will raise an error if the other resource does not exist.

A timer specifies the point during a Chef Infra Client run at which a notification is run. The following timers are available:

:before

Specifies that the action on a notified resource should be run before processing the resource block in which the notification is located.

:delayed

Default. Specifies that a notification should be queued up, and then executed at the end of a Chef Infra Client run.

:immediate, :immediately

Specifies that a notification should be run immediately, for each resource notified.

The syntax for subscribes is:

subscribes :action, 'resource[name]', :timer

Guards

A guard property can be used to evaluate the state of a node during the execution phase of a Chef Infra Client run. Based on the results of this evaluation, a guard property is then used to tell Chef Infra Client if it should continue executing a resource. A guard property accepts either a string value or a Ruby block value:

• A string is executed as a shell command. If the command returns 0, the guard is applied. If the command returns any other value, then the guard property is not applied. String guards in a powershell_script run Windows PowerShell commands and may return true in addition to 0.
• A block is executed as Ruby code that must return either true or false. If the block returns true, the guard property is applied. If the block returns false, the guard property is not applied.

A guard property is useful for ensuring that a resource is idempotent by allowing that resource to test for the desired state as it is being executed, and then if the desired state is present, for Chef Infra Client to do nothing.

The following properties can be used to define a guard that is evaluated during the execution phase of a Chef Infra Client run:

not_if

Prevent a resource from executing when the condition returns true.

only_if

Allow a resource to execute only if the condition returns true.

Examples

The following examples demonstrate various approaches for using the dsc_resource resource in recipes:

Open a Zip file

dsc_resource 'example' do
   resource :archive
   property :ensure, 'Present'
   property :path, 'C:\Users\Public\Documents\example.zip'
   property :destination, 'C:\Users\Public\Documents\ExtractionPath'
 end

Manage users and groups

dsc_resource 'demogroupadd' do
  resource :group
  property :groupname, 'demo1'
  property :ensure, 'present'
end

dsc_resource 'useradd' do
  resource :user
  property :username, 'Foobar1'
  property :fullname, 'Foobar1'
  property :password, ps_credential('P@assword!')
  property :ensure, 'present'
end

dsc_resource 'AddFoobar1ToUsers' do
  resource :Group
  property :GroupName, 'demo1'
  property :MembersToInclude, ['Foobar1']
end

Create and register a windows service

The following example creates a windows service, defines it’s execution path, and prevents windows from starting the service in case the executable is not at the defined location:

dsc_resource 'NAME' do
  resource :service
  property :name, 'NAME'
  property :startuptype, 'Disabled'
  property :path, 'D:\\Sites\\Site_name\file_to_run.exe'
  property :ensure, 'Present'
  property :state, 'Stopped'
end

Create a test message queue

The following example creates a file on a node (based on one that is located in a cookbook), unpacks the MessageQueue.zip Windows PowerShell module, and then uses the dsc_resource to ensure that Message Queuing (MSMQ) sub-features are installed, a test queue is created, and that permissions are set on the test queue:

cookbook_file 'cMessageQueue.zip' do
  path "#{Chef::Config[:file_cache_path]}\\MessageQueue.zip"
  action :create_if_missing
end

windows_zipfile "#{ENV['PROGRAMW6432']}\\WindowsPowerShell\\Modules" do
  source "#{Chef::Config[:file_cache_path]}\\MessageQueue.zip"
  action :unzip
end

dsc_resource 'install-sub-features' do
  resource :windowsfeature
  property :ensure, 'Present'
  property :name, 'msmq'
  property :IncludeAllSubFeature, true
end

dsc_resource 'create-test-queue' do
  resource :cPrivateMsmqQueue
  property :ensure, 'Present'
  property :name, 'Test_Queue'
end

dsc_resource 'set-permissions' do
  resource :cPrivateMsmqQueuePermissions
  property :ensure, 'Present'
  property :name, 'Test_Queue_Permissions'
  property :QueueNames, 'Test_Queue'
  property :ReadUsers, node['msmq']['read_user']
end

Example to show usage of module properties

dsc_resource 'test-cluster' do
  resource :xCluster
  module_name 'xFailOverCluster'
  module_version '1.6.0.0'
  property :name, 'TestCluster'
  property :staticipaddress, '10.0.0.3'
  property :domainadministratorcredential, ps_credential('abcd')
end