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 every 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 (Bash, csh, Perl, Python, or Ruby). This resource may also use any of the actions and attributes 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

The syntax for using the script resource in a recipe is as follows:

script "name" do
  some_attribute "value" # see attributes section below
  ...
  action :action # see actions section below
end

where

  • script tells the chef-client to use one of the following providers during the chef-client run: Chef::Resource::Script, Chef::Resource::Script::Bash, Chef::Resource::Script::Csh, Chef::Resource::Script::Perl, Chef::Resource::Script::Python, or Chef::Resource::Script::Ruby. The provider that is used by the chef-client depends on the platform of the machine on which the run is taking place
  • name is the name of the resource block; when the command attribute is not specified as part of a recipe, name is also the name of the command to be executed
  • attribute is zero (or more) of the attributes that are available for this resource
  • :action is the step that the resource will ask the provider to take during the chef-client run

Actions

This resource has the following actions:

Action Description
:run Default. Use to run a script.
:nothing Use to prevent a command from running. This action is used to specify that a command is run only when another resource notifies it.

Attributes

This resource has the following attributes:

Attribute Description
code A quoted (” ”) string of code to be executed.
command The name of the command to be executed. Default value: the name of the resource block (see Syntax section above).
creates Use to prevent a command from creating a file when that file already exists.
cwd The current working directory.
environment A Hash of environment variables in the form of {"ENV_VARIABLE" => "VALUE"}. (These variables must exist for a command to be run successfully.)
flags One (or more) command line flags that are passed to the interpreter when a command is invoked.
group The group name or group ID that must be changed before running a command.
interpreter The script interpreter to be used during code execution.
path 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 Optional. Use to specify a provider by using its long name. For example: provider Chef::Provider::Long::Name. See the Providers section below for the list of providers available to this resource.
returns 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.
timeout The amount of time (in seconds) a command will wait before timing out. Default value: 3600.
user The user name or user ID that should be changed before running a command.
umask The file mode creation mask, or umask.

Guards

A guard attribute 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 attribute is then used to tell the chef-client if it should continue executing a resource. A guard attribute 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 attribute is not applied.
  • A block is executed as Ruby code that must return either true or false. If the block returns true, the guard attribute is applied. If the block returns false, the guard attribute is not applied.

A guard attribute 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 attributes can be used to define a guard that is evaluated during the execution phase of the chef-client run:

Guard Description
not_if Use to prevent a resource from executing when the condition returns true.
only_if Use to 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 attributes:

Argument Description
:user

Use to specify the user that a command will run as. For example:

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

Use to specify the group that a command will run as. For example:

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

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

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

Use to set the current working directory before running a command. For example:

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

Use to 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 attribute to specify a script-based resource: bash, csh, perl, powershell_script, python, and ruby, plus the batch resource.

Attributes

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

Value Description
:bash Use to evaluate a string command using the bash resource.
:batch Use to evaluate a string command using the batch resource.
:csh Use to evaluate a string command using the csh resource.
:default Default. Use to execute the default interpreter as identified by the chef-client.
:perl Use to evaluate a string command using the perl resource.
:powershell_script Use to evaluate a string command using the powershell_script resource.
:python Use to evaluate a string command using the python resource.
:ruby Use to evaluate a string command using the ruby resource.

Inheritance

All non-default interpreters will not inherit arguments that are available to guard attributes unless the guard_interpreter attribute is specified. For example, the following resource block will not inherit the environment attribute (and requires that the environment variable be specified within the not_if guard in addition to the resource block itself):

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

and the following resource block will inherit the environment attribute:

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

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

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.exists?("#{key_dir}/server.crt") }
end

where code contains the OpenSSL command to be run. The not_if method 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 "0644"
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 "0644"
  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