Learning MCollective

Chapter 1. Introduction

What Is MCollective?

MCollective provides a framework for parallel job execution. It is commonly used to orchestrate change across clusters of servers in near real time. It is not entirely inaccurate to imagine the classic marionette controller with puppets dancing on strings. (Yes it’s a pun, but it is more apt than you may realize.)

MCollective is an adjunct tool in your toolbox that cooperates and enhances the capabilities of configuration management tools like Puppet, Chef, and Salt. Whereas these tools analyze and act to ensure complete configuration consistency, MCollective orchestrates specific and often singular actions across systems significantly faster.

Let’s talk about the difference between MCollective and using Chef, Puppet, Capistrano, Salt Overstack, or hand-built tools for orchestration. You may have used a parallel execution command like pssh before. You may have built or improved one yourself. And if you have, you’re familiar with their limitations, which include any or all of the following: 

• Loops through systems in order, processing a few at a time

• Simplistic (or overly complex) authentication mechanisms

• Requires customization for each alternative environment

• Unable to respond to deviations in response

• Too easy to overlook fatal error messages output to the screen

• Doesn’t support or extend existing management tools

MCollective differs from these tools in a wide variety of ways:

• Uses a masterless environment that allows ...