Chef

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script

A resource defines the desired state for a single configuration item present on a node that is under management by Chef. A resource collection—one (or more) individual resources—defines the desired state for the entire node. During a chef-client run, the current state of each resource is tested, after which the chef-client will take any steps that are necessary to repair the node and bring it back into the desired state.

Use the script resource to execute scripts using a specified interpreter, such as Bash, csh, Perl, Python, or Ruby. 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 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.

This resource is the base resource for several other resources used for scripting on specific platforms. For more information about specific resources for specific platforms, see the following topics:

Syntax

A script resource block typically executes scripts using a specified interpreter, such as Bash, csh, Perl, Python, or Ruby:

script 'extract_module' do
  interpreter "bash"
  cwd ::File.dirname(src_filepath)
  code <<-EOH
    mkdir -p #{extract_path}
    tar xzf #{src_filename} -C #{extract_path}
    mv #{extract_path}/*/* #{extract_path}/
    EOH
  not_if { ::File.exists?(extract_path) }
end

where

  • interpreter specifies the command shell to use
  • cwd specifies the directory from which the command is run
  • code specifies the command to run

It is more common to use the script-based resource that is specific to the command shell. Chef has shell-specific resources for Bash, csh, Perl, Python, and Ruby.

The same command as above, but run using the bash resource:

bash 'extract_module' do
  cwd ::File.dirname(src_filepath)
  code <<-EOH
    mkdir -p #{extract_path}
    tar xzf #{src_filename} -C #{extract_path}
    mv #{extract_path}/*/* #{extract_path}/
    EOH
  not_if { ::File.exists?(extract_path) }
end

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

script 'name' do
  code                       String
  creates                    String
  cwd                        String
  environment                Hash
  flags                      String
  group                      String, Integer
  interpreter                String
  notifies                   # see description
  path                       Array
  provider                   Chef::Provider::Script
  returns                    Integer, Array
  subscribes                 # see description
  timeout                    Integer, Float
  user                       String, Integer
  umask                      String, Integer
  action                     Symbol # defaults to :run if not specified
end

where

  • script is the resource
  • name is the name of the resource block
  • cwd is the location from which the command is run
  • :action identifies the steps the chef-client will take to bring the node into the desired state
  • code, creates, cwd, environment, flags, group, interpreter, path, provider, returns, timeout, user, and umask 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

This resource has the following actions:

Action Description
: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

This resource has the following attributes:

Attribute Description
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 Types: String, Integer

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

ignore_failure

Ruby Types: TrueClass, FalseClass

Continue running a recipe if a resource fails for any reason. Default value: false.

interpreter

Ruby Type: String

The script interpreter to use during code execution.

notifies

Ruby Type: Symbol, ‘Chef::Resource[String]’, Symbol

Which resource takes action when this resource’s state changes. A resource may notify more than one resource; use a notifies statement for each resource to be notified.

Specify the :action, 'resource[name]', and timer (:delayed or :immediately). Use multiple notifies statements to notify more than one resource.

resource 'name' do
  ...
  notifies :action, 'resource[name]', :timer
end

Use the following timers to specify when a notification is triggered:

Timer Description
:delayed Use to specify that a notification should be queued up, and then executed at the very end of a chef-client run.
:immediately Use to specify that a notification should be run immediately, per resource notified.
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.

provider

Ruby Type: Chef Class

Optional. Explicitly specify a provider. See “Providers” section below for more information.

retries

Ruby Type: Integer

The number of times to catch exceptions and retry the resource. Default value: 0.

retry_delay

Ruby Type: Integer

The retry delay (in seconds). Default value: 2.

returns

Ruby Types: Integer, Array

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. Default value: 0.

subscribes

Ruby Type: Symbol, ‘Chef::Resource[String]’, Symbol

Specify that this resource is to listen to another resource, and then take action when that resource’s state changes.

Specify the :action, 'resource[name]', and timer (:delayed or :immediately). Use multiple subscribes statements to listen to more than one resource.

resource 'name' do
  ...
  subscribes :action, 'resource[name]', :timer
end

The subscribes property uses the same timers as the notifies property.

timeout

Ruby Types: Integer, Float

The amount of time (in seconds) a command is to wait before timing out. Default value: 3600.

user

Ruby Types: String, Integer

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

umask

Ruby Types: 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:

Guard Description
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:

Argument Description
: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

Guard Interpreter

Any resource that passes a string command may also specify the interpreter that will be used to evaluate that string command. This is done by using the guard_interpreter property to specify a script-based resource.

Attributes

The guard_interpreter property may be set to any of the following values:

Value Description
:bash Evaluates a string command using the bash resource.
:batch Evaluates a string command using the batch resource. Default value (within a batch resource block): :batch.
:csh Evaluates a string command using the csh resource.
:default Default. Executes the default interpreter as identified by the chef-client.
:perl Evaluates a string command using the perl resource.
:powershell_script Evaluates a string command using the powershell_script resource. Default value (within a batch resource block): :powershell_script.
:python Evaluates a string command using the python resource.
:ruby Evaluates a string command using the ruby resource.

Inheritance

The guard_interpreter property is set to :default by default for the bash, csh, perl, python, and ruby resources. When the guard_interpreter property is set to :default, not_if or only_if guard statements do not inherit properties that are defined by the script-based resource.

Warning

The batch and powershell_script resources inherit properties by default. The guard_interpreter property is set to :batch or :powershell_script automatically when using a not_if or only_if guard statement within a batch or powershell_script resource, respectively.

For example, the not_if guard statement in the following resource example does not inherit the environment property:

bash 'javatooling' do
  environment {'JAVA_HOME' => '/usr/lib/java/jdk1.7/home'}
  code 'java-based-daemon-ctl.sh -start'
  not_if 'java-based-daemon-ctl.sh -test-started'
end

and requires adding the environment property to the not_if guard statement so that it may use the JAVA_HOME path as part of its evaluation:

bash 'javatooling' do
  environment {'JAVA_HOME' => '/usr/lib/java/jdk1.7/home'}
  code 'java-based-daemon-ctl.sh -start'
  not_if 'java-based-daemon-ctl.sh -test-started', :environment => {'JAVA_HOME' => '/usr/lib/java/jdk1.7/home'}
end

To inherit properties, add the guard_attribute property to the resource block and set it to the appropriate value:

  • :bash for bash
  • :csh for csh
  • :perl for perl
  • :python for python
  • :ruby for ruby

For example, using the same example as from above, but this time adding the guard_interpreter property and setting it to :bash:

bash 'javatooling' do
  guard_interpreter :bash
  environment {'JAVA_HOME' => '/usr/lib/java/jdk1.7/home'}
  code 'java-based-daemon-ctl.sh -start'
  not_if 'java-based-daemon-ctl.sh -test-started'
end

The not_if statement now inherits the environment property and will use the JAVA_HOME path as part of its evaluation.

Example

For example, the following code block will ensure the command is evaluated using the default intepreter as identified by the chef-client:

resource 'name' do
  guard_interpreter :default
  # code
end

Providers

Where a resource represents a piece of the system (and its desired state), a provider defines the steps that are needed to bring that piece of the system from its current state into the desired state.

The chef-client will determine the correct provider based on configuration data collected by Ohai at the start of the chef-client run. This configuration data is then mapped to a platform and an associated list of providers.

Generally, it’s best to let the chef-client choose the provider and this is (by far) the most common approach. However, in some cases specifying a provider may be desirable. There are two approaches:

  • Use a more specific short name—yum_package "foo" do instead of package "foo" do, script "foo" do instead of bash "foo" do, and so on—when available
  • Use the provider property within the resource block to specify the long name of the provider as an property of a resource. For example: provider Chef::Provider::Long::Name

The following providers are available. Use the short name to use the provider in a recipe:

Long name Short name Notes
Chef::Provider::Script script When this short name is used, the chef-client will determine the correct provider during the chef-client run.
Chef::Provider::Script::Bash bash The provider that is used with the Bash command interpreter.
Chef::Provider::Script::Csh csh The provider that is used with the csh command interpreter.
Chef::Provider::Script::Perl perl The provider that is used with the Perl command interpreter.
Chef::Provider::Script::Python python The provider that is used with the Python command interpreter.
Chef::Provider::Script::Ruby ruby The provider that is used with the Ruby command interpreter.

Examples

The following examples demonstrate various approaches for using resources in recipes. If you want to see examples of how Chef uses resources in recipes, take a closer look at the cookbooks that Chef authors and maintains: https://github.com/opscode-cookbooks.

Use a named provider to run a script

bash 'install_something' do
  user 'root'
  cwd '/tmp'
  code <<-EOH
  wget http://www.example.com/tarball.tar.gz
  tar -zxf tarball.tar.gz
  cd tarball
  ./configure
  make
  make install
  EOH
end

Run a script

script 'install_something' do
  interpreter 'bash'
  user 'root'
  cwd '/tmp'
  code <<-EOH
  wget http://www.example.com/tarball.tar.gz
  tar -zxf tarball.tar.gz
  cd tarball
  ./configure
  make
  make install
  EOH
end

or something like:

bash 'openvpn-server-key' do
  environment('KEY_CN' => 'server')
  code <<-EOF
    openssl req -batch -days #{node['openvpn']['key']['expire']} \
      -nodes -new -newkey rsa:#{key_size} -keyout #{key_dir}/server.key \
      -out #{key_dir}/server.csr -extensions server \
      -config #{key_dir}/openssl.cnf
  EOF
  not_if { File.exist?('#{key_dir}/server.crt') }
end

where code contains the OpenSSL command to be run. The not_if property tells the chef-client not to run the command if the file already exists.

Install a file from a remote location using bash

The following is an example of how to install the foo123 module for Nginx. This module adds shell-style functionality to an Nginx configuration file and does the following:

  • Declares three variables
  • Gets the Nginx file from a remote location
  • Installs the file using Bash to the path specified by the src_filepath variable
# the following code sample is similar to the ``upload_progress_module``
# recipe in the ``nginx`` cookbook:
# https://github.com/opscode-cookbooks/nginx

src_filename = "foo123-nginx-module-v#{
  node['nginx']['foo123']['version']
}.tar.gz"
src_filepath = "#{Chef::Config['file_cache_path']}/#{src_filename}"
extract_path = "#{
  Chef::Config['file_cache_path']
  }/nginx_foo123_module/#{
  node['nginx']['foo123']['checksum']
}"

remote_file 'src_filepath' do
  source node['nginx']['foo123']['url']
  checksum node['nginx']['foo123']['checksum']
  owner 'root'
  group 'root'
  mode '0755'
end

bash 'extract_module' do
  cwd ::File.dirname(src_filepath)
  code <<-EOH
    mkdir -p #{extract_path}
    tar xzf #{src_filename} -C #{extract_path}
    mv #{extract_path}/*/* #{extract_path}/
    EOH
  not_if { ::File.exists?(extract_path) }
end

Install an application from git using bash

The following example shows how Bash can be used to install a plug-in for rbenv named ruby-build, which is located in git version source control. First, the application is synchronized, and then Bash changes its working directory to the location in which ruby-build is located, and then runs a command.

 git "#{Chef::Config[:file_cache_path]}/ruby-build" do
   repository 'git://github.com/sstephenson/ruby-build.git'
   reference 'master'
   action :sync
 end

 bash 'install_ruby_build' do
   cwd '#{Chef::Config[:file_cache_path]}/ruby-build'
   user 'rbenv'
   group 'rbenv'
   code <<-EOH
     ./install.sh
     EOH
   environment 'PREFIX' => '/usr/local'
end

To read more about ruby-build, see here: https://github.com/sstephenson/ruby-build.

Store certain settings

The following recipe shows how an attributes file can be used to store certain settings. An attributes file is located in the attributes/ directory in the same cookbook as the recipe which calls the attributes file. In this example, the attributes file specifies certain settings for Python that are then used across all nodes against which this recipe will run.

Python packages have versions, installation directories, URLs, and checksum files. An attributes file that exists to support this type of recipe would include settings like the following:

default['python']['version'] = '2.7.1'

if python['install_method'] == 'package'
  default['python']['prefix_dir'] = '/usr'
else
  default['python']['prefix_dir'] = '/usr/local'
end

default['python']['url'] = 'http://www.python.org/ftp/python'
default['python']['checksum'] = '80e387...85fd61'

and then the methods in the recipe may refer to these values. A recipe that is used to install Python will need to do the following:

  • Identify each package to be installed (implied in this example, not shown)
  • Define variables for the package version and the install_path
  • Get the package from a remote location, but only if the package does not already exist on the target system
  • Use the bash resource to install the package on the node, but only when the package is not already installed
#  the following code sample comes from the ``oc-nginx`` cookbook on |github|: https://github.com/cookbooks/oc-nginx

version = node['python']['version']
install_path = "#{node['python']['prefix_dir']}/lib/python#{version.split(/(^\d+\.\d+)/)[1]}"

remote_file "#{Chef::Config[:file_cache_path]}/Python-#{version}.tar.bz2" do
  source "#{node['python']['url']}/#{version}/Python-#{version}.tar.bz2"
  checksum node['python']['checksum']
  mode '0755'
  not_if { ::File.exists?(install_path) }
end

bash 'build-and-install-python' do
  cwd Chef::Config[:file_cache_path]
  code <<-EOF
    tar -jxvf Python-#{version}.tar.bz2
    (cd Python-#{version} && ./configure #{configure_options})
    (cd Python-#{version} && make && make install)
  EOF
  not_if { ::File.exists?(install_path) }
end