About Recipes

[edit on GitHub]

A recipe is the most fundamental configuration element within the organization. A recipe:

• Is authored using Ruby, which is a programming language designed to read and behave in a predictable manner
• Is mostly a collection of resources, defined using patterns (resource names, attribute-value pairs, and actions); helper code is added around this using Ruby, when needed
• Must define everything that is required to configure part of a system
• Must be stored in a cookbook
• May be included in another recipe
• May use the results of a search query and read the contents of a data bag (including an encrypted data bag)
• May have a dependency on one (or more) recipes
• Must be added to a run-list before it can be used by Chef Infra Client
• Is always executed in the same order as listed in a run-list

Recipe Attributes

An attribute can be defined in a cookbook (or a recipe) and then used to override the default settings on a node. When a cookbook is loaded during a Chef Infra Client run, these attributes are compared to the attributes that are already present on the node. Attributes that are defined in attribute files are first loaded according to cookbook order. For each cookbook, attributes in the default.rb file are loaded first, and then additional attribute files (if present) are loaded in lexical sort order. When the cookbook attributes take precedence over the default attributes, Chef Infra Client applies those new settings and values during a Chef Infra Client run on the node.

Attribute Types

Chef Infra Client uses six types of attributes to determine the value that is applied to a node during a Chef Infra Client run. In addition, Chef Infra Client gathers attribute values from up to five locations. The combination of attribute types and sources makes up to 15 different competing values available during a Chef Infra Client run:

Attribute Persistence

All attributes except for normal attributes are reset at the beginning of a Chef Infra Client run. Attributes set via chef-client -j with a JSON file have normal precedence and are persisted between Chef Infra Client runs. Chef Infra Client rebuilds these attributes using automatic attributes collected by Ohai at the beginning of each Chef Infra Client run, and then uses default and override attributes that are specified in cookbooks, roles, environments, and Policyfiles. All attributes are then merged and applied to the node according to attribute precedence. The attributes that were applied to the node are saved to the Chef Infra Server as part of the node object at the conclusion of each Chef Infra Client run.

Attribute Precedence

Attributes are always applied by Chef Infra Client in the following order:

1. A default attribute located in a cookbook attribute file
2. A default attribute located in a recipe
3. A default attribute located in an environment
4. A default attribute located in a role
5. A force_default attribute located in a cookbook attribute file
6. A force_default attribute located in a recipe
7. A normal attribute located in a JSON file passed via chef-client -j
8. A normal attribute located in a cookbook attribute file
9. A normal attribute located in a recipe
10. An override attribute located in a cookbook attribute file
11. An override attribute located in a recipe
12. An override attribute located in a role
13. An override attribute located in an environment
14. A force_override attribute located in a cookbook attribute file
15. A force_override attribute located in a recipe
16. An automatic attribute identified by Ohai at the start of a Chef Infra Client run

where the last attribute in the list is the one that is applied to the node.

Attribute precedence, viewed from the same perspective as the overview diagram, where the numbers in the diagram match the order of attribute precedence:

Attribute precedence, when viewed as a table:

Blocklist Attributes

Attributes that should not be saved by a node may be blocklisted in the client.rb file. The blocklist is a Hash of keys that specify each attribute to be filtered out.

Attributes are blocklisted by attribute type, with each attribute type being blocklisted independently. Each attribute type—automatic, default, normal, and override—may define blocklists by using the following settings in the client.rb file:

Blocklisting Ohai (automatic) Attributes

The recommended practice is to use blocked_automatic_attributes to block attributes populated by Ohai’s system information gathering. Ohai gathers a large number of attributes that can consume a signicant amount of storage space on the Chef Infra Server. Many of these attributes may be considered highly valuable, while others could be blocklisted without any impact to data available in search. Normal, default, and override attributes are typically much more important attributes used within cookbooks and are more likely to cause issues if they are blocklisted incorrectly.

For example, automatic attribute data similar to:

{
  "filesystem" => {
    "/dev/disk0s2" => {
      "size" => "10mb"
    },
    "map - autohome" => {
      "size" => "10mb"
    }
  },
  "network" => {
    "interfaces" => {
      "eth0" => {...},
      "eth1" => {...},
    }
  }
}

To blocklist the filesystem attributes and allow the other attributes to be saved, update the client.rb file:

blocked_automatic_attributes ['filesystem']

When a blocklist is defined, any attribute of that type that is not specified in that attribute blocklist will be saved. So based on the previous blocklist for automatic attributes, the filesystem and map - autohome attributes will not be saved, but the network attributes will.

For attributes that contain slashes (/) within the attribute value, such as the filesystem attribute '/dev/diskos2', use an array. For

example:

blocked_automatic_attributes [['filesystem', '/dev/diskos2']]

Blocklist Attributes

Attributes that should be saved by a node may be allowlisted in the client.rb file. The allowlist is a hash of keys that specifies each attribute to be saved.

Attributes are allowlisted by attribute type, with each attribute type being allowlisted independently. Each attribute type—automatic, default, normal, and override—may define allowlists by using the following settings in the client.rb file:

Allowlisting Ohai (automatic) Attributes

The recommended practice is to use allowed_automatic_attributes to allow specific attributes populated by Ohai’s system information gathering. Ohai gathers a large number of attributes that can consume a signicant amount of storage space on the Chef Infra Server. Many of these attributes may be considered highly valuable, while others could be skipped without any impact to data available in search. Normal, default, and override attributes are typically much more important attributes used within cookbooks and are more likely to cause issues if they are ommited from an allowlist incorrectly.

For example, automatic attribute data similar to:

{
  "filesystem" => {
    "/dev/disk0s2" => {
      "size" => "10mb"
    },
    "map - autohome" => {
      "size" => "10mb"
    }
  },
  "network" => {
    "interfaces" => {
      "eth0" => {...},
      "eth1" => {...},
    }
  }
}

To allowlist the network attributes and prevent the other attributes from being saved, update the client.rb file:

allowed_automatic_attributes ['network/interfaces/']

When a allowlist is defined, any attribute of that type that is not specified in that attribute allowlist will not be saved. So based on the previous allowlist for automatic attributes, the filesystem and map - autohome attributes will not be saved, but the network attributes will.

Leave the value empty to prevent all attributes of that attribute type from being saved:

allowed_automatic_attributes []

For attributes that contain slashes (/) within the attribute value, such as the filesystem attribute '/dev/diskos2', use an array. For example:

allowed_automatic_attributes [['filesystem', '/dev/diskos2']]

File Methods

Use the following methods within the attributes file for a cookbook or within a recipe. These methods correspond to the attribute type of the same name:

• override
• default
• normal
• _unless

Environment Variables

In UNIX, a process environment is a set of key-value pairs made available to a process. Programs expect their environment to contain information required for the program to run. The details of how these key-value pairs are accessed depends on the API of the language being used.

If processes is started by using the execute or script resources (or any of the resources based on those two resources, such as bash), use the environment attribute to alter the environment that will be passed to the process.

bash 'env_test' do
  code <<-EOF
  echo $FOO
EOF
  environment ({ 'FOO' => 'bar' })
end

The only environment being altered is the one being passed to the child process that is started by the bash resource. This will not affect the Chef Infra Client environment or any child processes.

Work with Recipes

The following sections show approaches to working with recipes.

Use Data Bags

Data bags store global variables as JSON data. Data bags are indexed for searching and can be loaded by a cookbook or accessed during a search.

The contents of a data bag can be loaded into a recipe. For example, a data bag named apps and a data bag item named my_app:

{
  "id": "my_app",
  "repository": "git://github.com/company/my_app.git"
}

can be accessed in a recipe, like this:

my_bag = data_bag_item('apps', 'my_app')

The data bag item’s keys and values can be accessed with a Hash:

my_bag['repository'] #=> 'git://github.com/company/my_app.git'

Secret Keys

Encrypting a data bag item requires a secret key. A secret key can be created in any number of ways. For example, OpenSSL can be used to generate a random number, which can then be used as the secret key:

openssl rand -base64 512 | tr -d '\r\n' > encrypted_data_bag_secret

where encrypted_data_bag_secret is the name of the file which will contain the secret key. For example, to create a secret key named “my_secret_key”:

openssl rand -base64 512 | tr -d '\r\n' > my_secret_key

The tr command eliminates any trailing line feeds. Doing so avoids key corruption when transferring the file between platforms with different line endings.

Store Keys on Nodes

An encryption key can also be stored in an alternate file on the nodes that need it and specify the path location to the file inside an attribute; however, EncryptedDataBagItem.load expects to see the actual secret as the third argument, rather than a path to the secret file. In this case, you can use EncryptedDataBagItem.load_secret to slurp the secret file contents and then pass them:

# inside your attribute file:
# default[:mysql][:secretpath] = 'C:\\chef\\any_secret_filename'
#
# inside your recipe:
# look for secret in file pointed to by mysql attribute :secretpath
mysql_secret = Chef::EncryptedDataBagItem.load_secret('#{node['mysql']['secretpath']}')
mysql_creds = Chef::EncryptedDataBagItem.load('passwords', 'mysql', mysql_secret)
mysql_creds['pass'] # will be decrypted

Assign Dependencies

If a cookbook has a dependency on a recipe that is located in another cookbook, that dependency must be declared in the metadata.rb file for that cookbook using the depends keyword.

For example, if the following recipe is included in a cookbook named my_app:

include_recipe 'apache2::mod_ssl'

Then the metadata.rb file for that cookbook would have:

depends 'apache2'

Include Recipes

A recipe can include one (or more) recipes from cookbooks by using the include_recipe method. When a recipe is included, the resources found in that recipe will be inserted (in the same exact order) at the point where the include_recipe keyword is located.

The syntax for including a recipe is like this:

include_recipe 'recipe'

For example:

include_recipe 'apache2::mod_ssl'

Multiple recipes can be included within a recipe. For example:

include_recipe 'cookbook::setup'
include_recipe 'cookbook::install'
include_recipe 'cookbook::configure'

If a specific recipe is included more than once with the include_recipe method or elsewhere in the run_list directly, only the first instance is processed and subsequent inclusions are ignored.

Reload Attributes

Attributes sometimes depend on actions taken from within recipes, so it may be necessary to reload a given attribute from within a recipe. For example:

ruby_block 'some_code' do
  block do
    node.from_file(run_context.resolve_attribute('COOKBOOK_NAME', 'ATTR_FILE'))
  end
  action :nothing
end

Use Ruby

Anything that can be done with Ruby can be used within a recipe, such as expressions (if, unless, etc.), case statements, loop statements, arrays, hashes, and variables. In Ruby, the conditionals nil and false are false; every other conditional is true.

Assign a value

A variable uses an equals sign (=) to assign a value.

To assign a value to a variable:

package_name = 'apache2'

Use Case Statement

A case statement can be used to compare an expression, and then execute the code that matches.

To select a package name based on platform:

package 'apache2' do
  case node['platform']
  when 'centos', 'redhat', 'fedora', 'suse'
    package_name 'httpd'
  when 'debian', 'ubuntu'
    package_name 'apache2'
  when 'arch'
    package_name 'apache'
  end
  action :install
end

Check Conditions

An if expression can be used to check for conditions (true or false).

To check for condition only for Debian and Ubuntu platforms:

if platform?('debian', 'ubuntu')
  # do something if node['platform'] is debian or ubuntu
else
  # do other stuff
end

Execute Conditions

An unless expression can be used to execute code when a condition returns a false value (effectively, an unless expression is the opposite of an if statement).

To use an expression to execute when a condition returns a false value:

unless node['platform_version'] == '5.0'
  # do stuff on everything but 5.0
end

Loop over Array

A loop statement is used to execute a block of code one (or more) times. A loop statement is created when .each is added to an expression that defines an array or a hash. An array is an integer-indexed collection of objects. Each element in an array can be associated with and referred to by an index.

To loop over an array of package names by platform:

['apache2', 'apache2-mpm'].each do |p|
  package p
end

Loop over Hash

A hash is a collection of key-value pairs. Indexing for a hash is done using arbitrary keys of any object (as opposed to the indexing done by an array). The syntax for a hash is: key => "value".

To loop over a hash of gem package names:

{ 'fog' => '0.6.0', 'highline' => '1.6.0' }.each do |g, v|
  gem_package g do
    version v
  end
end

Apply to Run-lists

A recipe must be assigned to a run-list using the appropriate name, as defined by the cookbook directory and namespace. For example, a cookbook directory has the following structure:

cookbooks/
  apache2/
    recipes/
      default.rb
      mod_ssl.rb

There are two recipes: a default recipe (that has the same name as the cookbook) and a recipe named mod_ssl. The syntax that applies a recipe to a run-list is similar to:

{
  'run_list': [
  'recipe[cookbook_name::default_recipe]',
  'recipe[cookbook_name::recipe_name]'
  ]
}

where ::default_recipe is implied (and does not need to be specified). On a node, these recipes can be assigned to a node’s run-list similar to:

{
  'run_list': [
  'recipe[apache2]',
  'recipe[apache2::mod_ssl]'
  ]
}

Chef Infra Server

Use knife to add a recipe to the run-list for a node. For example:

knife node run list add NODENAME "recipe[apache2]"

More than one recipe can be added:

% knife node run list add NODENAME "recipe[apache2],recipe[mysql],role[ssh]"

which creates a run-list similar to:

run_list:
   recipe[apache2]
   recipe[mysql]
   role[ssh]

chef-solo

Use a JSON file to pass run-list details to chef-solo as long as the cookbook in which the recipe is located is available to the system on which chef-solo is running. For example, a file named dna.json contains the following details:

{
  "run_list": ["recipe[apache2]"]
}

To add the run-list to the node, enter the following:

sudo chef-solo -j /etc/chef/dna.json

Use Search Results

Search indexes allow queries to be made for any type of data that is indexed by the Chef Infra Server, including data bags (and data bag items), environments, nodes, and roles. A defined query syntax is used to support search patterns like exact, wildcard, range, and fuzzy. A search is a full-text query that can be done from several locations, including from within a recipe, by using the search subcommand in knife, the search method in the Recipe DSL, the search box in the Chef management console, and by using the /search or /search/INDEX endpoints in the Chef Infra Server API. The search engine is based on Elasticsearch and is run from the Chef Infra Server.

The results of a search query can be loaded into a recipe. For example, a very simple search query (in a recipe) might look like this:

search(:node, 'attribute:value')

A search query can be assigned to variables and then used elsewhere in a recipe. For example, to search for all nodes that have a role assignment named webserver, and then render a template which includes those role assignments:

webservers = search(:node, 'role:webserver')

template '/tmp/list_of_webservers' do
  source 'list_of_webservers.erb'
  variables(webservers: webservers)
end

Use Tags

A tag is a custom description that is applied to a node. A tag, once applied, can be helpful when managing nodes using knife or when building recipes by providing alternate methods of grouping similar types of information.

Tags can be added and removed. Machines can be checked to see if they already have a specific tag. To use tags in your recipe simply add the following:

tag('mytag')

To test if a machine is tagged, add the following:

tagged?('mytag')

to return true or false. tagged? can also use an array as an argument.

To remove a tag:

untag('mytag')

For example:

tag('machine')

if tagged?('machine')
  Chef::Log.info("Hey I'm #{node['tags']}")
end

untag('machine')

unless tagged?('machine')
  Chef::Log.info('I am not tagged')
end

Will return something like this:

[Thu, 22 Jul 2010 18:01:45 +0000] INFO: Hey I'm machine
[Thu, 22 Jul 2010 18:01:45 +0000] INFO: I has no tagz

End Chef Infra Client Run

Sometimes it may be necessary to stop processing a recipe and/or stop processing the entire Chef Infra Client run. There are a few ways to do this:

• Use the return keyword to stop processing a recipe based on a condition, but continue processing a Chef Infra Client run
• Use the raise keyword to stop a Chef Infra Client run by triggering an unhandled exception
• Use a rescue block in Ruby code
• Use an exception handler

The following sections show various approaches to ending a Chef Infra Client run.

return Keyword

The return keyword can be used to stop processing a recipe based on a condition, but continue processing a Chef Infra Client run. For example:

file '/tmp/name_of_file' do
  action :create
end

return if platform?('windows')

package 'name_of_package' do
  action :install
end

where platform?('windows') is the condition set on the return keyword. When the condition is met, stop processing the recipe. This approach is useful when there is no need to continue processing, such as when a package cannot be installed. In this situation, it’s OK for a recipe to stop processing.

raise Keyword

In certain situations it may be useful to stop a Chef Infra Client run entirely by using an unhandled exception. The raise keyword can be used to stop a Chef Infra Client run in both the compile and execute phases.

Use these keywords in a recipe—but outside of any resource blocks—to trigger an unhandled exception during the compile phase. For example:

file '/tmp/name_of_file' do
  action :create
end

raise "message" if platform?('windows')

package 'name_of_package' do
  action :install
end

where platform?('windows') is the condition that will trigger the unhandled exception.

Use these keywords in the ruby_block resource to trigger an unhandled exception during the execute phase. For example:

ruby_block "name" do
  block do
    # Ruby code with a condition, e.g. if ::File.exist?(::File.join(path, "/tmp"))
    raise "message"  # e.g. "Ordering issue with file path, expected foo"
  end
end

Use these keywords in a class. For example:

class CustomError < StandardError; end

and then later on:

def custom_error
  raise CustomError, "error message"
end

or:

def custom_error
  raise CustomError, "error message"
end

Rescue Blocks

Since recipes are written in Ruby, they can be written to attempt to handle error conditions using the rescue block.

For example:

begin
  dater = data_bag_item(:basket, 'flowers')
rescue Net::HTTPClientException
  # maybe some retry code here?
  raise 'message_to_be_raised'
end

where data_bag_item makes an HTTP request to the Chef Infra Server to get a data bag item named flowers. If there is a problem, the request will return a Net::HTTPClientException. The rescue block can be used to try to retry or otherwise handle the situation. If the rescue block is unable to handle the situation, then the raise keyword is used to specify the message to be raised.

node.run_state

Use node.run_state to stash transient data during a Chef Infra Client run. This data may be passed between resources, and then evaluated during the execution phase. run_state is an empty Hash that is always discarded at the end of a Chef Infra Client run.

For example, the following recipe will install the Apache web server, randomly choose PHP or Perl as the scripting language, and then install that scripting language:

package 'httpd' do
  action :install
end

ruby_block 'randomly_choose_language' do
  block do
    if Random.rand > 0.5
      node.run_state['scripting_language'] = 'php'
    else
      node.run_state['scripting_language'] = 'perl'
    end
  end
end

package 'scripting_language' do
  package_name lazy { node.run_state['scripting_language'] }
  action :install
end

where:

• The ruby_block resource declares a block of Ruby code that is run during the execution phase of a Chef Infra Client run
• The if statement randomly chooses PHP or Perl, saving the choice to node.run_state['scripting_language']
• When the package resource has to install the package for the scripting language, it looks up the scripting language and uses the one defined in node.run_state['scripting_language']
• lazy {} ensures that the package resource evaluates this during the execution phase of a Chef Infra Client run (as opposed to during the compile phase)

When this recipe runs, Chef Infra Client will print something like the following:

* ruby_block[randomly_choose_language] action run
 - execute the ruby block randomly_choose_language

* package[scripting_language] action install
 - install version 5.3.3-27.el6_5 of package php