05-writing-tasks

Writing Tasks

Difficulty: Basic

Time: Approximately 15 minutes

In this exercise you will write your first Puppet Tasks for use with Bolt.

• How do tasks work?
• Write your first task in Bash
• Write your first task in PowerShell
• Write your first task in Python

Prerequisites

Complete the following before you start this lesson:

1. Installing Bolt
2. Setting up test nodes
3. Running Commands
4. Running Scripts

How do tasks work?

Tasks are similar to scripts, you can implement them in any language that runs on your target nodes. But tasks are kept in modules and can have metadata. This allows you to reuse and share them more easily. You can upload and download tasks as modules from the Puppet Forge, run them from GitHub or use them locally to organize your regularly used commands.

Tasks are stored in the tasks directory of a module, a module being a directory with a unique name. You can have several tasks per module, but the init task is special and runs by default if you do not specify a task name.

By default tasks take arguments as environment variables prefixed with PT (short for Puppet Tasks).

Write your first task in Bash

This exercise uses sh, but you can use Perl, Python, Lua, or JavaScript or any language that can read environment variables or take content on stdin.

1. Save the following file to modules/exercise5/tasks/init.sh:

   #!/bin/sh
   
   echo $(hostname) received the message: $PT_message
   

2. Run the exercise5 task. Note the message argument. This will be expanded to the PT_message environment variable expected by our task. By naming parameters explicitly it's easier for others to use your tasks.

   bolt task run exercise5 message=hello --nodes node1 --modulepath ./modules
   

   The result:

   Started on node1...
   Finished on node1:
     localhost.localdomain received the message: hello
     {
     }
   Successful on 1 node: node1
   Ran on 1 node in 0.99 seconds
   

3. Run the Bolt command with a different value for message and see how the output changes.

Write your first task in PowerShell

If you're targeting Windows nodes then you might prefer to implement the task in PowerShell.

1. Save the following file as modules/exercise5/tasks/print.ps1

   param ($message)
   Write-Output "$env:computername received the message: $message"

2. Run the exercise5 task.

   bolt task run exercise5::print message="hello powershell" --nodes $WINNODE --modulepath ./modules --no-ssl
   

   The result:
   Started on localhost...
   Finished on localhost:
     Nano received the message: hello powershell
     {
     }
   Successful on 1 node: winrm://vagrant:vagrant@localhost:55985
   Ran on 1 node in 3.87 seconds
   

   Note:

   • The name of the file on disk (minus any file extension) translates to the name of the task when run via Bolt, in this case print.
   • The name of the module (directory) is also used to find the relevant task, in this case exercise5.
   • As with the Bash example above, name parameters so that they're more easily understood by users of the task.
   • By default tasks with a .ps1 extension executed over WinRM use PowerShell standard agrument handling rather than being supplied as prefixed environment variables or via stdin.

Write your first task in Python

Note that Bolt assumes that the required runtime is already available on the target nodes. For the following examples to work, Python 2 or 3 must be installed on the target nodes. This task will also work on Windows system with Python 2 or 3 installed.

1. Save the following as modules/exercise5/tasks/gethost.py:

   #!/usr/bin/env python
   
   import socket
   import sys
   import os
   import json
   
   host = os.environ.get('PT_host')
   result = { 'host': host }
   
   if host:
       result['ipaddr'] = socket.gethostbyname(host)
       result['hostname'] = socket.gethostname()
       # The _output key is special and used by bolt to display a human readable summary
       result['_output'] = "%s is available at %s on %s" % (host, result['ipaddr'], result['hostname'])
       print(json.dumps(result))
   else:
       # The _error key is special. Bolt will print the 'msg' in the error for the user.
       result['_error'] = { 'msg': 'No host argument passed', 'kind': 'exercise5/missing_parameter' }
       print(json.dumps(result))
       sys.exit(1)

2. Run the task using the command bolt task run <task-name> <task options>.

   bolt task run exercise5::gethost host=google.com --nodes all --modulepath ./modules
   

   The result:

   Started on node1...
   Finished on node1:
     google.com is available at 172.217.3.206 on localhost.localdomain
     {
       "host": "google.com",
       "hostname": "localhost.localdomain",
       "ipaddr": "172.217.3.206"
     }
   Successful on 1 node: node1
   Ran on 1 node in 0.97 seconds
   

Next steps

Now that you know how to write tasks you can move on to:

Downloading and running existing tasks