Writing plans in YAML

Sections

YAML plans run a list of steps in order, which allows you to define simple workflows. Steps can contain embedded Puppet code expressions to add logic where necessary.

Naming plans

Plan names are named based on the filename of the plan, the name of the module containing the plan, and the path to the plan within the module.

Place plan files in your module's ./plans directory, using these file extensions:

  • Puppet plans — .pp

  • YAML plans — .yaml, not .yml

Plan names are composed of two or more name segments, indicating:

  • The name of the module the plan is located in.

  • The name of the plan file, without the extension.

  • The path within the module, if the plan is in a subdirectory of ./plans.

For example, given a module called mymodule with a plan defined in ./mymodule/plans/myplan.pp, the plan name is mymodule::myplan. A plan defined in ./mymodule/plans/service/myplan.ppwould be mymodule::service::myplan. This name is how you refer to the plan when you run commands.

The plan filename init is special: the plan it defines is referenced using the module name only. For example, in a module called mymodule, the plan defined in init.pp is the mymodule plan.

Avoid giving plans the same names as constructs in the Puppet language. Although plans do not share their namespace with other language constructs, giving plans these names makes your code difficult to read.

Each plan name segment must begin with a lowercase letter and:

  • May include lowercase letters.

  • May include digits.

  • May include underscores.

  • Must not be a reserved word.

  • Must not have the same name as any Puppet data types.

  • Namespace segments must match the following regular expression \A[a-z][a-z0-9_]*\Z

Plan structure

YAML plans contain a list of steps with optional parameters and results.

YAML maps accept these keys:

  • steps: The list of steps to perform

  • parameters: (Optional) The parameters accepted by the plan

  • return: (Optional) The value to return from the plan

Steps key

The steps key is an array of step objects, each of which corresponds to a specific action to take.

When the plan runs, each step is executed in order. If a step fails, the plan halts execution and raises an error containing the result of the step that failed.

Steps use these fields:

  • name: (Optional) A unique name that can be used to refer to the result of the step later.

  • description: (Optional) An explanation of what the step is doing.

Other available keys depend on the type of step.

Message step

Use a message step to print a message. This will print a message to standard out (stdout) when using the human output format, and print to standard error (stderr) when using the json output format.

Message steps use a single field:

  • message: The message to print

For example:

steps:
  - message: hello world

You can pass variables to the message step to print them to stdout. If the variable contains a valid plan result, Bolt formats the plan result using a JSON representation of the result object. If the object is not a plan result, Bolt prints the object as a string.

For information on printing a step result with message, see Debugging plans.

Command step

Use a command step to run a single command on a list of targets and save the results, containing stdout, stderr, and exit code.

The step fails if the exit code of any command is non-zero.

Command steps use these fields:

  • command: The command to run

  • targets: A target or list of targets to run the command on

For example:

steps:
  - command: hostname -f
    targets:
      - web1.example.com
      - web2.example.com
      - web3.example.com
    description: "Get the webserver hostnames"

Task step

Use a task step to run a Bolt task on a list of targets and save the results.

Task steps use these fields:

  • task: The task to run

  • targets: A target or list of targets to run the task on

  • parameters: (Optional) A map of parameter values to pass to the task

For example:

steps:
  - task: package
    targets:
      - web1.example.com
      - web2.example.com
      - web3.example.com
    description: "Check the version of the openssl package on the webservers"
    parameters:
      action: status
      name: openssl

Script step

Use a script step to run a script on a list of targets and save the results.

The script must be in the files/ directory of a module. The name of the script must be specified as <modulename>/path/to/script, omitting the files directory from the path.

Script steps use these fields:

  • script: The script to run

  • targets: A target or list of targets to run the script on

  • arguments: (Optional) An array of command-line arguments to pass to the script

For example:

steps:
  - script: mymodule/check_server.sh
    targets:
      - web1.example.com
      - web2.example.com
      - web3.example.com
    description: "Run mymodule/files/check_server.sh on the webservers"
    arguments:
      - "/index.html"
      - 60

File download step

Use a file download step to download a file or directory from a list of targets to a destination directory on the local host.

Files and directories are downloaded to the destination directory within a subdirectory matching the target's URL-encoded safe name. If the destination directory is a relative path, it will expand relative to the project's downloads directory, <project>/downloads.

File download steps use these fields:

  • download: The location of the remote file to download

  • destination: The destination directory to download the file to

  • targets: A target or list of targets to download the file from

For example:

steps:
  - download: /etc/ssh/sshd_config
    destination: sshd_config
    targets:
      - web1.example.com
      - ssh://web2.example.com
      - web3
    description: "Download ssh daemon config from the webservers"

If the specified file exists on each of the targets, it would be saved to the following locations:

  • ~/.puppetlabs/bolt/downloads/sshd_config/web1.example.com/sshd_config

  • ~/.puppetlabs/bolt/downloads/sshd_config/ssh%3A%2F%2Fweb2.example.com/sshd_config

  • ~/.puppetlabs/bolt/downloads/sshd_config/web3/sshd_config

Since files are downloaded to a directory matching the target's safe name, the target's safe name is URL encoded to ensure it's a valid directory name.

🔩 Tip: To avoid URL encoding the target's safe name, give the target a simple, human-readable name in your inventory file.

File upload step

Use a file upload step to upload a file to a specific location on a list of targets.

The file to upload must be in the files/ directory of a Puppet module. The source for the file must be specified as <modulename>/path/to/file, omitting the files directory from the path.

File upload steps use these fields:

  • upload: The location of the local file to be uploaded

  • destination: The remote location to upload the file to

  • targets: A target or list of targets to upload the file to

For example:

steps:
  - upload: mymodule/motd.txt
    destination: /etc/motd
    targets:
      - web1.example.com
      - web2.example.com
      - web3.example.com
    description: "Upload motd to the webservers"

Plan step

Use a plan step to run another plan and save its result.

Plan steps use these fields:

  • plan: The name of the plan to run

  • parameters: (Optional) A map of parameter values to pass to the plan

For example:

steps:
  - plan: facts
    description: "Gather facts for the webservers using the built-in facts plan"
    parameters:
      targets:
        - web1.example.com
        - web2.example.com
        - web3.example.com

Resources step

Use a resources step to apply a list of Puppet resources. A resource defines the desired state for part of a target. Bolt ensures each resource is in its desired state. Like the steps in a plan, if any resource in the list fails, the rest are skipped.

For each resources step, Bolt executes the apply_prep plan function against the targets specified with the targets field. For more information about apply_prep see the Applying manifest blocks section.

Resources steps use these fields:

  • resources: An array of resources to apply

  • targets: A target or list of targets to apply the resources on

Each resource is a YAML map with a type and title, and optionally a parameters key. The resource type and title can either be specified separately with the type and title keys, or can be specified in a single line by using the type name as a key with the title as its value.

For example:

steps:
  - resources:
    # This resource is type 'package' and title 'nginx'
    - package: nginx
      parameters:
        ensure: latest
    # This resource is type 'service' and title 'nginx'
    - type: service
      title: nginx
      parameters:
        ensure: running
    targets:
      - web1.example.com
      - web2.example.com
      - web3.example.com
    description: "Set up nginx on the webservers"

Parameters key

Plans accept parameters with the parameters key. The value of parameters is a map, where each key is the name of a parameter and the value is a map describing the parameter.

Parameter values can be referenced from steps as variables.

Parameters use these fields:

  • type: (Optional) A valid Puppet data type. The value supplied must match the type or the plan fails.

  • default: (Optional) Used if no value is given for the parameter

  • description: (Optional)

For example, this plan accepts a load_balancer name as a string, two sets of targets called frontends and backends, and a version string:

parameters:
  # A simple parameter definition doesn't need a type or description
  load_balancer:
  frontends:
    type: TargetSpec
    description: "The frontend web servers"
  backends:
    type: TargetSpec
    description: "The backend application servers"
  version:
    type: String
    description: "The new application version to deploy"

How strings are evaluated

The behavior of strings is defined by how they're written in the plan.

'single-quoted strings' are treated as string literals without any interpolation.

"double-quoted strings" are treated as Puppet language double-quoted strings with variable interpolation.

| block-style strings are treated as expressions of arbitrary Puppet code. Note the string itself must be on a new line after the | character.

bare strings are treated dynamically based on their content. If they begin with a $, they're treated as Puppet code expressions. Otherwise, they're treated as YAML literals.

Here's an example of different kinds of strings in use:

parameters:
  message:
    type: String
    default: "hello"

steps:
  - eval: hello
    description: 'This will evaluate to: hello'
  - eval: $message
    description: 'This will evaluate to: hello'
  - eval: '$message'
    description: 'This will evaluate to: $message'
  - eval: "${message} world"
    description: 'This will evaluate to: hello world'
  - eval: |
      [$message, $message, $message].join(" ")
    description: 'This will evaluate to: hello hello hello'

Using variables and simple expressions

Parameters and step results are available as variables during plan execution, and they can be used to compute the value for each field of a step.

The simplest way to use a variable is to reference it directly by name. For example, this plan takes a parameter called targets and passes it as the target list to a step:

parameters:
  targets:
    type: TargetSpec

steps:
  - command: hostname -f
    targets: $targets

Variables can also be interpolated into string values. The string must be double-quoted to allow interpolation. For example:

parameters:
  username:
    type: String

steps:
  - task: echo
    parameters:
      message: "hello ${username}"
    targets: $targets

Many operations can be performed on variables to compute new values for step parameters or other fields.

Indexing arrays or hashes

You can retrieve a value from an Array or a Hash using the [] operator. This operator can also be used when interpolating a value inside a string.

parameters:
  users:
    # Array[String] is a Puppet data type representing an array of strings
    type: Array[String]

steps:
  - task: user::add
    targets: 'host.example.com'
    parameters:
      name: $users[0]
  - task: echo
    targets: 'host.example.com'
    parameters:
      message: "hello ${users[0]}"

Calling functions

You can call a built-in Bolt function or Puppet function to compute a value.

parameters:
  users:
    type: Array[String]

steps:
  - task: user::add
    parameters:
      name: $users.first
  - task: echo
    message: "hello ${users.join(',')}"

Using code blocks

Some Puppet functions take a block of code as an argument. For instance, you can filter an array of items based on the result of a block of code.

The result of the filter function is an array here, not a string, because the expression isn't inside quotes.

parameters:
  numbers:
    type: Array[Integer]

steps:
  - task: sum
    description: "add up the numbers > 5"
    parameters:
      indexes: $numbers.filter |$num| { $num > 5 }

Connecting steps

You can connect multiple steps by using the result of one step to compute the parameters for another step.

name key

The name key makes its result available to later steps in a variable with that name.

This example uses the map function to get the value of stdout from each command result and then joins them into a single string separated by commas.

parameters:
  targets:
    type: TargetSpec

steps:
  - name: hostnames
    command: hostname -f
    targets: $targets
  - task: echo
    parameters:
      message: $hostnames.map |$hostname_result| { $hostname_result['stdout'] }.join(',')

eval step

The eval step evaluates an expression and saves the result in a variable. This is useful to compute a variable to use multiple times later.

parameters:
  count:
    type: Integer

steps:
  - name: double_count
    eval: $count * 2
  - task: echo
    targets: web1.example.com
    parameters:
      message: "The count is ${count}, and twice the count is ${double_count}"

Returning results

You can return a result from a plan by setting the return key at the top level of the plan. When the plan finishes, the return key is evaluated and returned as the result of the plan. If no return key is set, the plan returns undef.

steps:
  - name: hostnames
    command: hostname -f
    targets: $targets

return: $hostnames.map |$hostname_result| { $hostname_result['stdout'] }

Debugging plans

By default, Bolt does not print the result for each step to stdout. However, you can use one of the following methods to investigate a plan execution:

  • Each time you run a Bolt command, Bolt prints a debug log to a bolt-debug.log file in the root of your project directory.

  • Certain steps print to stdout when you use the --verbose CLI option.

  • You can print the result of any step to stdout using a message step.

  • You can adjust your log level for detailed information on how Bolt is executing your plan, including the results returned from each step.

Using the --verbose option for debugging

You can see the results for the following types of steps by running the plan with the --verbose CLI option:

  • commands

  • scripts

  • plans

  • tasks

Using a message step for debugging

You can print the result of a step to stdout by passing the step name to a message step as a parameter.

To print the result of a step to stdout using message, use the following structure:

- message: $<STEP_NAME> 

For example, the following plan uses a task step named check_mysql to run the package task and check for MySQL. A message step prints the result of the check_mysql task:

parameters:
  targets:
    type: TargetSpec   

steps:
  - name: check_mysql
    targets: $targets
    task: package
    parameters:
     action: status
     name: mysql
    description: "Check for MySQL"

  - message: $check_mysql

The output from this plan looks something like this:

Starting: plan wordpress::test
Starting: Check for MySQL on target1
Finished: Check for MySQL with 0 failures in 0.59 sec
[
  {
    "target": "target1",
    "action": "task",
    "object": "package",
    "status": "success",
    "value": {
      "status": "uninstalled",
      "version": ""
    }
  }
]
Finished: plan wordpress::test in 0.6 sec
Plan completed successfully with no result

Debug logs

Bolt logs additional information about a plan run, including output sent to standard error (stderr), at the debug level. Use the --log-level debug CLI option or the log configuration setting.

$ bolt task run mytask param1=foo param2=bar -t all --log-level debug

Each time you run a Bolt command, Bolt prints a debug level log to a bolt-debug.log file in the root of your project directory. You can disable the log file by specifying the following in your bolt-project.yaml:

log:
  bolt-debug.log: disable

Computing complex values

To compute complex values, you can use a Puppet code expression as the value of any field of a step except the name.

Bolt loads the plan as a YAML data structure. As it executes each step, it evaluates any expressions embedded in the step. Each plan parameter and the values of every previous named step are available in scope.

This lets you take advantage of the power of Puppet language in the places it's necessary, while keeping the rest of your plan simple.

When your plans need more sophisticated control flow or error handling beyond running a list of steps in order, it's time to convert them to Puppet language plans.

Applying Puppet code from Puppet Forge modules

Modules downloaded from the Puppet Forge often include Puppet code that you can use to simplify your workflow. The Puppet code in these modules can be applied to targets from a YAML plan using the resources step.

For example, if you wanted to install and configure Apache and MySQL on a group of targets, you could download the apache and mysql modules and apply the apache and mysql::server classes to the targets with a resources step. You can invoke a class as part of a resources step by using the syntax class: classname.

The following YAML plan accepts a list of targets and then installs and configures Apache and MySQL using classes from the apache and mysql modules:

description: Install and configure Apache and MySQL

parameters:
  targets:
    type: TargetSpec
    description: The targets to configure

steps:
  - description: Install and configure Apache and MySQL
    name: configure
    targets: $targets
    resources:
      - class: apache
      - class: mysql::server

return: $configure

Puppet code included in modules often accepts parameters. To set parameters, add a map of parameter names and values under the parameters key for a specific resource.

- class: apache
  parameters:
    user: apache
    manage_user: false

Converting YAML plans to Puppet language plans

You can convert a YAML plan to a Puppet language plan with the bolt plan convert command.

bolt plan convert path/to/my/plan.yaml

This command takes the relative or absolute path to the YAML plan to be converted and prints the converted Puppet language plan to stdout.

Note: Converting a YAML plan might result in a Puppet plan which is syntactically correct, but behaves differently. Always manually verify a converted Puppet language plan's functionality. There are some constructs that do not translate from YAML plans to Puppet language plans. These are listed below. If you convert a YAML plan to Puppet and it changes behavior, file an issue in Bolt's Git repo.

For example, with this YAML plan:

# site-modules/mymodule/plans/yamlplan.yaml
parameters:
  targets:
    type: TargetSpec
steps:
  - name: run_task
    task: sample
    targets: $targets
    parameters:
      message: "hello world"
return: $run_task

Run the following conversion:

$ bolt plan convert site-modules/mymodule/plans/yamlplan.yaml
# WARNING: This is an autogenerated plan. It may not behave as expected.
plan mymodule::yamlplan(
  TargetSpec $targets
) {
  $run_task = run_task('sample', $targets, {'message' => "hello world"})
  return $run_task
}

Quirks when converting YAML plans to Puppet language plans

There are some quirks and limitations associated with converting a plan expressed in YAML to a plan expressed in the Puppet language. In some cases it is impossible to accurately translate from YAML to Puppet. In others, code that is generated from the conversion is syntactically correct but not idiomatic Puppet code.

Named eval step

The eval step allows snippets of Puppet code to be expressed in YAML plans. When converting a multi-line eval step to Puppet code and storing the result in a variable, use the with lambda.

For example, here is a YAML plan with a multi-line eval step:

parameters:
  foo:
    type: Optional[Integer]
    description: foo
    default: 0

steps:
  - eval: |
      $x = $foo + 1
      $x * 2
    name: eval_step

return: $eval_step

And here is the same plan, converted to the Puppet language:

plan yaml_plans::with_lambda(
  Optional[Integer] $foo = 0
) {
  $eval_step = with() || {
    $x = $foo + 1
    $x * 2
  }

  return $eval_step
}

Writing this plan from scratch using the Puppet language, you would probably not use the lambda. In this example the converted Puppet code is correct, but not as natural or readable as it could be.

Resource step variable interpolation

When applying Puppet resources in a resource step, variable interpolation behaves differently in YAML plans and Puppet language plans. To illustrate this difference, consider this YAML plan:

steps:
  - targets: localhost
    description: Apply a file resource
    resources:
    - type: file
      title: '/tmp/foo'
      parameters:
        content: $facts['os']['family']
        ensure: present
  - name: file_contents
    description: Read contents of file managed with file resource
    eval: >
      file::read('/tmp/foo')
      
return: $file_contents

This plan performs apply_prep on a localhost target. Then it uses a Puppet file resource to write the OS family discovered from the Puppet $facts hash to a temporary file. Finally, it reads the value written to the file and returns it. Running bolt plan convert on this plan produces this Puppet code:

plan yaml_plans::interpolation_pp() {
  apply_prep('localhost')
  $interpolation = apply('localhost') {
    file { '/tmp/foo':
      content => $facts['os']['family'],
      ensure => 'present',
    }
  }
  $file_contents = file::read('/tmp/foo')

  return $file_contents
}

This Puppet language plan works as expected, whereas the YAML plan it was converted from fails. The failure stems from the $factsvariable being resolved as a plan variable, instead of being evaluated as part of compiling the manifest code in an applyblock.

Dependency order

The resources in a resources list are applied in order. It is possible to set dependencies explicitly, but when doing so you must refer to them in a particular way. Consider the following YAML plan:

parameters:
  targets:
    type: TargetSpec
steps:
  - name: pkg
    targets: $targets
    resources:
      - title: openssh-server
        type: package
        parameters:
          ensure: present
          before: File['/etc/ssh/sshd_config']
      - title: /etc/ssh/sshd_config
        type: file
        parameters:
          ensure: file
          mode: '0600'
          content: ''
          require: Package['openssh-server']

Executing this plan fails during catalog compilation because of how Bolt parses the resources referenced in the before and require parameters. You will see the error message Could not find resource 'File['/etc/ssh/sshd_config']' in parameter 'before'. The solution is to not quote the resource titles:

parameters:
  targets:
    type: TargetSpec
steps:
  - name: pkg
    targets: $targets
    resources:
      - title: openssh-server
        type: package
        parameters:
          ensure: present
          before: File[/etc/ssh/sshd_config]
      - title: /etc/ssh/sshd_config
        type: file
        parameters:
          ensure: file
          mode: '0600'
          content: ''
          require: Package[openssh-server]

In general, declare resources in order. This is an unusual example to illustrate a case where parameter parsing leads to non-intuitive results.

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