chef_gem resource¶

Warning

The chef_gem and gem_package resources are both used to install Ruby gems. For any machine on which Chef Infra Client is installed, there are two instances of Ruby. One is the standard, system-wide instance of Ruby and the other is a dedicated instance that is available only to Chef Infra Client. Use the chef_gem resource to install gems into the instance of Ruby that is dedicated to Chef Infra Client. Use the gem_package resource to install all other gems (i.e. install gems system-wide).

Use the chef_gem resource to install a gem only for the instance of Ruby that is dedicated to Chef Infra Client. When a gem is installed from a local file, it must be added to the node using the remote_file or cookbook_file resources.

The chef_gem resource works with all of the same properties and options as the gem_package resource, but does not accept the gem_binary property because it always uses the CurrentGemEnvironment under which Chef Infra Client is running. In addition to performing actions similar to the gem_package resource, the chef_gem resource does the following:

Runs its actions immediately, before convergence, allowing a gem to be used in a recipe immediately after it is installed
Runs Gem.clear_paths after the action, ensuring that gem is aware of changes so that it can be required immediately after it is installed

Syntax¶

A chef_gem resource block manages a package on a node, typically by installing it. The simplest use of the chef_gem resource is:

chef_gem 'package_name'

which will install the named gem using all of the default options and the default action (:install).

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

chef_gem 'name' do
  clear_sources              true, false
  compile_time               true, false
  gem_binary                 String
  include_default_source     true, false
  options                    String
  package_name               String
  source                     String, Array
  timeout                    String, Integer
  version                    String
  action                     Symbol # defaults to :install if not specified
end

where:

chef_gem 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.
clear_sources, compile_time, gem_binary, include_default_source, options, package_name, source, timeout, and version are the properties available to this resource.

Actions¶

The chef_gem resource has the following actions:

:install: Default. Install a gem. If a version is specified, install the specified version of the gem.
: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.
:purge: Purge a gem. This action typically removes the configuration files as well as the gem.
:reconfig: Reconfigure a gem. This action requires a response file.
:remove: Remove a gem.
:upgrade: Install a gem and/or ensure that a gem is the latest version.

Properties¶

The chef_gem resource has the following properties:

clear_sources

Ruby Type: true, false | Default Value: false

Set to true to download a gem from the path specified by the source property (and not from RubyGems).

Note

Another approach is to use the gem_package resource, and then specify the gem_binary location to the RubyGems directory that is used by Chef. For example:

gem_package 'gem_name' do
  gem_binary Chef::Util::PathHelper.join(Chef::Config.embedded_dir,'bin','gem')
  action :install
end

compile_time

Ruby Type: true, false | Default Value: false

Controls the phase during which a gem is installed on a node. Set to true to install a gem while the resource collection is being built (the “compile phase”). Set to false to install a gem while Chef Infra Client is configuring the node (the “converge phase”). Possible values: nil (for verbose warnings), true (to warn once per chef-client run), or false (to remove all warnings). Recommended value: false.

gem_binary

Ruby Type: String | Default Value: Chef's built-in gem binary

The path of a gem binary to use for the installation. By default, the same version of Ruby that is used by Chef Infra Client will be installed.

include_default_source

Ruby Type: true, false | Default Value: true

Set to false to not include Chef::Config[:rubygems_url] in the sources.

New in Chef Client 13.0.

options

Ruby Type: String, Hash, Array,

Options for the gem install, either a Hash or a String. When a hash is given, the options are passed to Gem::DependencyInstaller.new, and the gem will be installed via the gems API. When a String is given, the gem will be installed by shelling out to the gem command. Using a Hash of options with an explicit gem_binary will result in undefined behavior.

package_name

Ruby Type: String

An optional property to set the gem name if it differs from the resource block’s name.

source

Ruby Type: String, Array

Optional. The URL, or list of URLs, at which the gem package is located. This list is added to the source configured in Chef::Config[:rubygems_url] (see also include_default_source) to construct the complete list of rubygems sources. Users in an ‘airgapped’ environment should set Chef::Config[:rubygems_url] to their local RubyGems mirror.

timeout

Ruby Type: String, Integer

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

version

Ruby Type: String

The version of a gem to be installed or upgraded.

Common Resource Functionality¶

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

Common Properties¶

The following properties are common to every resource:

ignore_failure

Ruby Type: true, false | Default Value: false

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

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 retry delay (in seconds).

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.

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, per 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.

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, per 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.

Properties

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 resources in recipes:

Compile time vs. converge time installation of gems

To install a gem while Chef Infra Client is configuring the node (the “converge phase”), set the compile_time property to false:

chef_gem 'right_aws' do
  compile_time false
  action :install
end

To install a gem while the resource collection is being built (the “compile phase”), set the compile_time property to true:

chef_gem 'right_aws' do
  compile_time true
  action :install
end

Install MySQL for Chef

apt_update

build_essential 'install compilation tools' do
  compile_time true
end

chef_gem 'mysql'