About the Custom Resource DSL¶
Use the Custom Resource DSL to define property behaviors within custom resources, such as:
- Loading the value of a specific property
- Comparing the current property value against a desired property value
- Telling the chef-client when and how to make changes
action_class¶
The converge_if_changed
method may be used multiple times. The following example shows how to use the converge_if_changed
method to compare the multiple desired property values against the current property values (as loaded by the load_current_value
method).
property :path, String, name_property: true
property :content, String
property :mode, String
load_current_value do
if ::File.exist?(new_resource.path)
content IO.read(new_resource.path)
mode ::File.stat(new_resource.path).mode
end
end
action :create do
converge_if_changed :content do
IO.write(new_resource.path, new_resource.content)
end
converge_if_changed :mode do
::File.chmod(new_resource.mode, new_resource.path)
end
end
where
load_current_value
loads the property values for bothcontent
andmode
- A
converge_if_changed
block tests onlycontent
- A
converge_if_changed
block tests onlymode
The chef-client will only update the property values that require updates and will not make changes when the property values are already in the desired state
converge_if_changed¶
Use the converge_if_changed
method inside an action
block in a custom resource to compare the desired property values against the current property values (as loaded by the load_current_value
method). Use the converge_if_changed
method to ensure that updates only occur when property values on the system are not the desired property values and to otherwise prevent a resource from being converged.
To use the converge_if_changed
method, wrap it around the part of a recipe or custom resource that should only be converged when the current state is not the desired state:
action :some_action do
converge_if_changed do
# some property
end
end
For example, a custom resource defines two properties (content
and path
) and a single action (:create
). Use the load_current_value
method to load the property value to be compared, and then use the converge_if_changed
method to tell the chef-client what to do if that value is not the desired value:
property :content, String
property :path, String, name_property: true
load_current_value do
if ::File.exist?(path)
content IO.read(path)
end
end
action :create do
converge_if_changed do
IO.write(new_resource.path, new_resource.content)
end
end
When the file does not exist, the IO.write(new_resource.path, new_resource.content)
code is executed and the chef-client output will print something similar to:
Recipe: recipe_name::block
* resource_name[blah] action create
- update my_file[blah]
- set content to "hola mundo" (was "hello world")
Multiple Properties¶
The converge_if_changed
method may be used multiple times. The following example shows how to use the converge_if_changed
method to compare the multiple desired property values against the current property values (as loaded by the load_current_value
method).
property :path, String, name_property: true
property :content, String
property :mode, String
load_current_value do
if ::File.exist?(new_resource.path)
content IO.read(new_resource.path)
mode ::File.stat(new_resource.path).mode
end
end
action :create do
converge_if_changed :content do
IO.write(new_resource.path, new_resource.content)
end
converge_if_changed :mode do
::File.chmod(new_resource.mode, new_resource.path)
end
end
where
load_current_value
loads the property values for bothcontent
andmode
- A
converge_if_changed
block tests onlycontent
- A
converge_if_changed
block tests onlymode
The chef-client will only update the property values that require updates and will not make changes when the property values are already in the desired state
default_action¶
The default action in a custom resource is, by default, the first action listed in the custom resource. For example, action aaaaa
is the default resource:
property :property_name, RubyType, default: 'value'
...
action :aaaaa do
# the first action listed in the custom resource
end
action :bbbbb do
# the second action listed in the custom resource
end
The default_action
method may also be used to specify the default action. For example:
property :property_name, RubyType, default: 'value'
default_action :aaaaa
action :aaaaa do
# the first action listed in the custom resource
end
action :bbbbb do
# the second action listed in the custom resource
end
defines action aaaaa
as the default action. If default_action :bbbbb
is specified, then action bbbbb
is the default action. Use this method for clarity in custom resources, if deliberately stating the default resource is desired, or to specify a default action that is not listed first in the custom resource.
load_current_value¶
Use the load_current_value
method to load the specified property values from the node, and then use those values when the resource is converged. This method may take a block argument.
Use the load_current_value
method to guard against property values being replaced. For example:
load_current_value do
if ::File.exist?('/var/www/html/index.html')
homepage IO.read('/var/www/html/index.html')
end
if ::File.exist?('/var/www/html/404.html')
page_not_found IO.read('/var/www/html/404.html')
end
end
This ensures the values for homepage
and page_not_found
are not changed to the default values when the chef-client configures the node.
new_resource.property¶
Custom resources are designed to use core resources that are built into Chef. In some cases, it may be necessary to specify a property in the custom resource that is the same as a property in a core resource, for the purpose of overriding that property when used with the custom resource. For example:
resource_name :node_execute
property :command, String, name_property: true
property :version, String
# Useful properties from the `execute` resource
property :cwd, String
property :environment, Hash, default: {}
property :user, [String, Integer]
property :sensitive, [true, false], default: false
prefix = '/opt/languages/node'
load_current_value do
current_value_does_not_exist! if node.run_state['nodejs'].nil?
version node.run_state['nodejs'][:version]
end
action :run do
execute 'execute-node' do
cwd cwd
environment environment
user user
sensitive sensitive
# gsub replaces 10+ spaces at the beginning of the line with nothing
command <<-CODE.gsub(/^ {10}/, '')
#{prefix}/#{new_resource.version}/#{command}
CODE
end
end
where the property :cwd
, property :environment
, property :user
, and property :sensitive
are identical to properties in the execute resource, embedded as part of the action :run
action. Because both the custom properties and the execute properties are identical, this will result in an error message similar to:
ArgumentError
-------------
wrong number of arguments (0 for 1)
To prevent this behavior, use new_resource.
to tell the chef-client to process the properties from the core resource instead of the properties in the custom resource. For example:
resource_name :node_execute
property :command, String, name_property: true
property :version, String
# Useful properties from the `execute` resource
property :cwd, String
property :environment, Hash, default: {}
property :user, [String, Integer]
property :sensitive, [true, false], default: false
prefix = '/opt/languages/node'
load_current_value do
current_value_does_not_exist! if node.run_state['nodejs'].nil?
version node.run_state['nodejs'][:version]
end
action :run do
execute 'execute-node' do
cwd new_resource.cwd
environment new_resource.environment
user new_resource.user
sensitive new_resource.sensitive
# gsub replaces 10+ spaces at the beginning of the line with nothing
command <<-CODE.gsub(/^ {10}/, '')
#{prefix}/#{new_resource.version}/#{new_resource.command}
CODE
end
end
where cwd new_resource.cwd
, environment new_resource.environment
, user new_resource.user
, and sensitive new_resource.sensitive
correctly use the properties of the execute resource and not the identically-named override properties of the custom resource.
property¶
Use the property
method to define properties for the custom resource. The syntax is:
property :property_name, ruby_type, default: 'value', parameter: 'value'
where
:property_name
is the name of the propertyruby_type
is the optional Ruby type or array of types, such asString
,Integer
,true
, orfalse
default: 'value'
is the optional default value loaded into the resourceparameter: 'value'
optional parameters
For example, the following properties define username
and password
properties with no default values specified:
property :username, String
property :password, String
ruby_type¶
The property ruby_type is a positional parameter. Use to ensure a property value is of a particular ruby class, such as true
, false
, nil
, String
, Array
, Hash
, Integer
, Symbol
. Use an array of ruby classes to allow a value to be of more than one type. For example:
property :aaaa, Stringproperty :bbbb, Integerproperty :cccc, Hashproperty :dddd, [true, false]property :eeee, [String, nil]property :ffff, [Class, String, Symbol]property :gggg, [Array, Hash]
validators¶
A validation parameter is used to add zero (or more) validation parameters to a property.
Parameter | Description |
---|---|
:callbacks |
Use to define a collection of unique keys and values (a ruby hash) for which the key is the error message and the value is a lambda to validate the parameter. For example: callbacks: {
'should be a valid non-system port' => lambda {
|p| p > 1024 && p < 65535
}
}
|
:default |
Use to specify the default value for a property. For example: default: 'a_string_value'
default: 123456789
default: []
default: ()
default: {}
|
:equal_to |
Use to match a value with equal_to: [true, false]
equal_to: ['php', 'perl']
|
:regex |
Use to match a value to a regular expression. For example: regex: [ /^([a-z]|[A-Z]|[0-9]|_|-)+$/, /^\d+$/ ]
|
:required |
Indicates that a property is required. For example: required: true
|
:respond_to |
Use to ensure that a value has a given method. This can be a single method name or an array of method names. For example: respond_to: valid_encoding?
|
Some examples of combining validation parameters:
property :spool_name, String, regex: /$\w+/
property :enabled, equal_to: [true, false, 'true', 'false'], default: true
desired_state¶
Add desired_state:
to set the desired state property for a resource. This value may be true
or false
, and all properties default to true.
- When
true
, the state of the property is determined by the state of the system - When
false
, the value of the property impacts how the resource executes, but it is not determined by the state of the system.
For example, if you were to write a resource to create volumes on a cloud provider you would need define properties such as volume_name
, volume_size
, and volume_region
. The state of these properties would determine if your resource needed to converge or not. For the resource to function you would also need to define properties such as cloud_login
and cloud_password
. These are necessary properties for interacting with the cloud provider, but their state has no impact on decision to converge the resource or not, so you would set desired_state
to false
for these properties.
property :volume_name, String
property :volume_size, Integer
property :volume_region, String
property :cloud_login, String, desired_state: false
property :cloud_password, String, desired_state: false
identity¶
Add identity:
to set a resource to a particular set of properties. This value may be true
or false
.
- When
true
, data for that property is returned as part of the resource data set and may be available to external applications, such as reporting - When
false
, no data for that property is returned.
If no properties are marked true
, the property that defaults to the name
of the resource is marked true
.
For example, the following properties define username
and password
properties with no default values specified, but with identity
set to true
for the user name:
property :username, String, identity: true
property :password, String
Block Arguments¶
Any properties that are marked identity: true
or desired_state: false
will be available from load_current_value
. If access to other properties of a resource is needed, use a block argument that contains all of the properties of the requested resource. For example:
resource_name :file
load_current_value do |desired|
puts "The user typed content = #{desired.content} in the resource"
end
property_is_set?¶
Use the property_is_set?
method to check if the value for a property is set. The syntax is:
property_is_set?(:property_name)
The property_is_set?
method will return true
if the property is set.
For example, the following custom resource creates and/or updates user properties, but not their password. The property_is_set?
method checks if the user has specified a password and then tells the chef-client what to do if the password is not identical:
action :create do
converge_if_changed do
shell_out!("rabbitmqctl create_or_update_user #{username} --prop1 #{prop1} ... ")
end
if property_is_set?(:password)
if shell_out("rabbitmqctl authenticate_user #{username} #{password}").error?
converge_by "Updating password for user #{username} ..." do
shell_out!("rabbitmqctl update_user #{username} --password #{password}")
end
end
end
end
provides¶
Use the provides
method to associate a custom resource with the Recipe DSL on different operating systems. When multiple custom resources use the same DSL, specificity rules are applied to determine the priority, from highest to lowest:
- provides :resource_name, platform_version: ‘0.1.2’
- provides :resource_name, platform: ‘platform_name’
- provides :resource_name, platform_family: ‘platform_family’
- provides :resource_name, os: ‘operating_system’
- provides :resource_name
For example:
provides :my_custom_resource, platform: 'redhat' do |node|
node['platform_version'].to_i >= 7
end
provides :my_custom_resource, platform: 'redhat'
provides :my_custom_resource, platform_family: 'rhel'
provides :my_custom_resource, os: 'linux'
provides :my_custom_resource
This allows you to use multiple custom resources files that provide the same resource to the user, but for different operating systems or operation system versions. With this you can eliminate the need for platform or platform version logic within your resources.
override¶
Chef will warn you if the Recipe DSL is provided by another custom resource or built-in resource. For example:
class X < Chef::Resource
provides :file
end
class Y < Chef::Resource
provides :file
end
This will emit a warning that Y
is overriding X
. To disable this warning, use override: true
:
class X < Chef::Resource
provides :file
end
class Y < Chef::Resource
provides :file, override: true
end
reset_property¶
Use the reset_property
method to clear the value for a property as if it had never been set, and then use the default value. For example, to clear the value for a property named password
:
reset_property(:password)
resource_name¶
Note
Cookbook and custom resource names should contain only alphanumeric characters. A hyphen (-
) is a valid character and may be used in cookbook and custom resource names, but it is discouraged. The chef-client will return an error if a hyphen is not converted to an underscore (_
) when referencing from a recipe the name of a custom resource in which a hyphen is located.
Use the resource_name
method at the top of a custom resource to declare a custom name for that resource. For example:
resource_name :custom_name
where :custom_name
is the resource name as it may be used in a recipe. For example, a cookbook named website
and a custom resource file named httpd
is by default used in a recipe with website_httpd
. If :custom_name
is web_httpd
then it may be used like this:
web_httpd 'name' do
# properties
end
For example, the httpd.rb
file in the website
cookbook could be assigned a custom resource name like this:
resource_name :httpd
property :homepage, String, default: '<h1>Hello world!</h1>'
action :create do
package 'httpd'
service 'httpd' do
action [:enable, :start]
end
file '/var/www/html/index.html' do
content new_resource.homepage
end
end
and is then usable in a recipe like this:
httpd 'build website' do
homepage '<h1>Welcome to the Example Co. website!</h1>'
action :create
end