python resource¶

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Use the python resource to execute scripts using the Python interpreter. This resource may also use any of the actions and properties that are available to the execute resource. Commands that are executed with this resource are (by their nature) not idempotent, as they are typically unique to the environment in which they are run. Use not_if and only_if to guard this resource for idempotence.

Note

The python script resource (which is based on the script resource) is different from the ruby_block resource because Ruby code that is run with this resource is created as a temporary file and executed like other script resources, rather than run inline.

Syntax¶

The python resource has the following syntax:

python 'hello world' do
  code <<-EOH
    print "Hello world! From Chef and Python."
    EOH
end

where

code specifies the command to run

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

python 'name' do
  code             String
  command
  creates          String
  cwd              String
  default_env      true, false # default value: false
  domain           String
  elevated         true, false # default value: false
  environment      Hash
  flags            String
  group            String, Integer
  interpreter      String
  live_stream      true, false # default value: false
  password         String
  returns          Integer, Array # default value: 0
  sensitive        true, false
  timeout          Integer, Float
  umask            String, Integer
  user             String, Integer
  action           Symbol # defaults to :run if not specified
end

where:

python is the resource.
name is the name given to the resource block.
action identifies which steps the chef-client will take to bring the node into the desired state.
code, command, creates, cwd, default_env, domain, elevated, environment, flags, group, interpreter, live_stream, password, returns, sensitive, timeout, umask, and user are the properties available to this resource.

Actions¶

The python resource has the following actions:

:nothing: Prevent a command from running. This action is used to specify that a command is run only when another resource notifies it.
:run: Default. Run a script.

Properties¶

The python resource has the following properties:

code

Ruby Type: String

A quoted (” “) string of code to be executed.

creates

Ruby Type: String

Prevent a command from creating a file when that file already exists.

cwd

Ruby Type: String

The current working directory.

environment

Ruby Type: Hash

A Hash of environment variables in the form of ({"ENV_VARIABLE" => "VALUE"}). (These variables must exist for a command to be run successfully.)

flags

Ruby Type: String

One or more command line flags that are passed to the interpreter when a command is invoked.

group

Ruby Type: String, Integer

The group name or group ID that must be changed before running a command.

ignore_failure

Ruby Type: true, false | Default Value: false

Continue running a recipe if a resource fails for any reason.

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.

A timer specifies the point during the Chef 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 the Chef Client run.
:immediate, :immediately: Specifies that a notification should be run immediately, per resource notified.

The syntax for notifies is:

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

path

Ruby Type: Array

An array of paths to use when searching for a command. These paths are not added to the command’s environment $PATH. The default value uses the system path.

Warning

For example:

python 'mycommand' do
  environment 'PATH' => "/my/path/to/bin:#{ENV['PATH']}"
end

retries

Ruby Type: Integer | Default Value: 0

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

retry_delay

Ruby Type: Integer | Default Value: 2

The retry delay (in seconds).

returns

Ruby Type: Integer, Array | Default Value: 0

The return value for a command. This may be an array of accepted values. An exception is raised when the return value(s) do not match.

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.

A timer specifies the point during the Chef 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 the Chef Client run.
:immediate, :immediately: Specifies that a notification should be run immediately, per resource notified.

The syntax for subscribes is:

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

timeout

Ruby Type: Integer, Float | Default Value: 3600

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

user

Ruby Type: String, Integer

The user name or user ID that should be changed before running a command.

umask

Ruby Type: String, Integer

The file mode creation mask, or umask.

Guards¶

A guard property can be used to evaluate the state of a node during the execution phase of the chef-client run. Based on the results of this evaluation, a guard property is then used to tell the chef-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 the chef-client to do nothing.

Attributes

The following properties can be used to define a guard that is evaluated during the execution phase of the chef-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.

Arguments

The following arguments can be used with the not_if or only_if guard properties:

:user

Specify the user that a command will run as. For example:

not_if 'grep adam /etc/passwd', :user => 'adam'

:group

Specify the group that a command will run as. For example:

not_if 'grep adam /etc/passwd', :group => 'adam'

:environment

Specify a Hash of environment variables to be set. For example:

not_if 'grep adam /etc/passwd', :environment => {
  'HOME' => '/home/adam'
}

:cwd

Set the current working directory before running a command. For example:

not_if 'grep adam passwd', :cwd => '/etc'

:timeout

Set a timeout for a command. For example:

not_if 'sleep 10000', :timeout => 10

Examples¶

None.