Chef InSpec Inputs

What are Inputs?

Inputs are the “knobs” you can use to customize the behavior of Chef InSpec profiles. If a profile supports inputs, you can set the inputs in a variety of ways, allowing flexibility. Profiles that include other profiles can set inputs in the included profile, enabling a multi-layered approach to configuring profiles.

A Simple Example

Suppose you have a profile named rock_critic. In its profile metadata file (inspec.yml):

# Optionally declare inputs in the profile metadata
# This lets you set up things like type checking, etc.
inputs:
- name: amplifier_max_volume
  description: How loud the amplifiers can go
  type: numeric
  # More options, including value: and priority: are possible here

In the profile’s control code:

# Set a default value for an input.  This is optional.
input('amplifier_max_volume', value: 10)

control 'Big Rock Show' do
  describe input('amplifier_max_volume') do    # This line reads the value of the input
    it { should eq 11 } # The UK'S LOUDEST BAND
  end
end

When the above profile is executed by using inspec exec rock_critic, you would see something like:

  11
     ×  should eq 10

     expected: 10
          got: 11

     (compared using ==)
Test Summary: 0 successful, 1 failure, 0 skipped

That result clearly won’t do. Let’s override the input’s default value. Create a file, custom_amps.yml:

amplifier_max_volume: 11

We can now run that profile with inspec exec rock_critic --input-file custom_amps.yaml:

  11
     ✔  should eq 11

Test Summary: 1 successful, 0 failures, 0 skipped

Which profiles support inputs?

The best way for a profile to indicate it supports inputs is to list them in the metadata file, inspec.yml. Any profile that has an inputs (or the deprecated attributes) section in its inspec.yml metadata file is configuring inputs.

That said, any profile that uses the DSL keyword input() (or the deprecated attribute()) in the control source code supports inputs. These profiles are reading (and possibly setting) input values and using them to make decisions.

How can I set Inputs?

As installed (without specialized plugins), Chef InSpec supports five ways of setting inputs:

  • Inline in control code, using input('input_name', value: 42).
  • In profile inspec.yml metadata files
  • Using the CLI option --input-file somefile.yaml
  • In kitchen-inspec, using the verifier/inputs settings
  • In the Audit Cookbook, using the node[:audit][:inputs]

In addition, Chef InSpec supports Input Plugins, which can provide optional integrations to specific key-value stores.

How does Input precedence work?

Simple Precedence

Briefly:

inline DSL < metadata < ( cli-input-file or kitchen-inspec or audit-cookbook )

In addition, for inherited profiles:

dependent profile metadata < wrapper profile metadata

This precedence lets you override input values on the command line, as well as override child profile inline values from the parent profile. This description matches the general behavior of InSpec v3, while also making some edge cases easier to reason.

The Details of Input Precedence

Whenever an input provider sets a value on an input, a priority value is assigned to the operation. Over the life of the input, multiple assignments with varying priority values may occur. When the input is evaluated, the current value is determined by finding the setting event with the highest priority.

Note that this approach does not rely on execution order, nor does it rely on multiple named precedence levels. Each setting operation is preserved and this allows the user to debug the history of the input values.

Some input providers allow you to set a priority when you set the value. For example, to set a priority of 50 in a metadata file, use:

inputs:
- name: very_important_input
  value: 12
  priority: 50

To set a priority in DSL, use: ruby input('also_important', value: 42, priority: 45)

As packaged, Chef InSpec uses the following priority values:

Input Provider Priority May change priority
Inline DSL 20 Yes
Metadata 30 Yes
Metadata in a wrapper cookbook 35 Yes
CLI --input-file option 40 No
inspec-kitchen inputs: section 40 No
audit cookbook node[:audit][:inputs] 40 No

What happened to “Attributes”?

When originally introduced, the Input facility was named Attributes. This name was problematic, because:

  • The Chef Infra tool uses the same word to describe its parameterization system.
  • Chef Infra attributes have a completely different and much more complex precedence system.
  • This caused confusion about passing Chef Infra attributes into InSpec when using Audit Cookbook and kitchen-inspec.

Based on these concerns, InSpec attributes have been renamed to InSpec inputs in Chef InSpec v4.

Support for using the DSL keyword attribute(), the metadata field attributes:, and the corresponding kitchen-inspec and audit cookbook values are anticipated to continue through Chef InSpec v5.

Working with Inputs in Control Code

Input Scope

Inputs are available throughout the InSpec profile DSL. You can use them anywhere.

# some_controls.rb

input('outer_input', value: 1) # here

control 'control-1' do
  input('control_dsl_input', value: 2) # here too
  describe some_resource do
    input('test_dsl_input', value: 3) # even here
    it { should cmp input('expectation_dsl_input') } # and yes here too
  end
end

Setting Inputs in Control DSL

When you write input('some_name', value: 'some_value'), you are setting an input value in the DSL. Because the value: option is present, a new value will be set. You may also pass any other option listed in the input option reference.

Reading Inputs in Control DSL

When you call input('some_name'), with or without additional options, the value of the input will be resolved and returned. Note that this process may involve sourcing the value from another provider, using the value set in DSL, or overriding the value provided in the same call.


# You can use the value in a Ruby variable
some_var = input('some_input_name')

# Or more directly in a resource parameter
describe file(input('important_path')) do
  it { should exist }
end

# Or as the resource itself (this could be a string, here)
describe input('some_setting') do
  it { should cmp 'correct_value' }
end

# Or as the expected value
describe file('/etc/httpd/httpd.conf') do
  its('owner') { should_not cmp input('webserver_user') }
end

The value returned can be used anywhere a Ruby value is used.

Configuring Inputs in Profile Metadata

Each Chef InSpec profile has a metadata file at the top level named inspec.yml. In that file, you may add a section for inputs. You may define inputs there, clearly setting options including values, type checking, and whether the input is required.

name: my_profile
inputs:
- name: webserver_user  # Name is the only required field
- name: favorite_fruit
  value: banana         # You can set a value; priority is 30 for metadata
- name: meaning_of_life
  type: Numeric
  value: 42
  required: true
  priority: 70

All input options are supported in metadata files.

There are two major advantages to defining inputs in profile metadata: 1. The inputs and their configuration are listed explicitly in simple YAML in one place - a consumer of your profile does not need to read through the control code to find the inputs. 2. You can set inputs in other profiles that you depend on using profile inheritance.

Using inputs with Profile inheritance

When your profile relies on another profile using the depends key in the metadata file, you can set — that is, override — the value of the input in the dependent profile by including the profile option and naming the dependent profile.

# child inspec.yml
name: child
inputs:
- name: favorite_food
  value: pizza
# wrapper inspec.yml
name: wrapper
depends:
- name: child
  path: ../child
inputs:
- name: favorite_food
  value: broccoli
  profile: child       # <----- REQUIRED to override the value in InSpec 4

In Chef InSpec 4+, every input is namespaced. For example, you could have an input named wrapper/favorite_food and one named child/favorite_food. If no explicit profile option is set within the wrapper profile metadata file, then wrapper is assumed to be the profile.

Setting Input values using --input-file

You may also provide inputs and values via YAML files on the command line. The format can be seen below:

an_input: a_value
another_input: another_value

CLI-set inputs have a priority of 40.

As of Chef InSpec 4.3.2, this mechanism has the following limitations:

  1. No input options may be set - only the name and value.
  2. Because the CLI is outside the scope of any individual profile and the inputs don’t take options, the inputs are clumsily copied into every profile, effectively making the CLI mechanism global.

Input Options Reference

Name

Required String. This option identifies the input.

Allowed in: All. When used in DSL and Metadata, the name is unique within the current profile. When used in CLI input files, audit cookbook, and kitchen-inspec, the input is copied across all profiles using the same name.

Description

Optional String. Human-meaningful explanation of the input.

Allowed in: DSL, Metadata

Value

Optional, any Ruby or YAML type. This is the value that will be available when you read the input. See the Reading Inputs section for more information.

Allowed in: All

Type

Optional, String. This value must be one of String, Numeric, Regexp, Array, Hash, Boolean, or Any. If provided, the value of the input will be checked to see if it is of the corresponding type. Note that Regexp indicates that the input value itself should be a regular expression, not that it should match any particular regular expression.

Allowed in: DSL, Metadata

Required

Optional, true or false. If true, a control using the input will be failed if it reads the value when none has been set.

Allowed in: DSL, Metadata

Priority

Optional, Integer, 0-100. Higher values make this assignment have higher precedence. This is an advanced feature.

Allowed in: DSL, Metadata

Profile

Optional, String. Allows you to set an input in another profile from your profile.

Allowed in: DSL, Metadata

Advanced Topics

Debugging Inputs with the Event Log

If it is difficult to determine why a particular value is being used, you can use the Event Log to determine what is happening.

First, use the input_object() DSL method. This method is like input() in that it looks up an input, but instead of evaluating the current value, it returns the underlying Inspec::Input object.


puts input_object('troublesome_input').diagnostic_string

# Or
require 'pp'
pp input_object('troublesome_input').events

diagnostic_string assembles the Event Log into a printable log message for convenience.

The Event Log contains entries for every time that the value changed, as well as one for when the input was first created. When possible, stack probing is used to determine file and line numbers. Most importantly, you will see priority numbers; remember that highest priority wins; order only matters to break a tie.