Puppet Zero

Idempotence -- not just a big & scary word

You may have read some docs, or stopped by the #puppet IRC channel. You've likely read a blog post or two. You've probably run across the word idempotence or have been chastised for writing non-idempotent Puppet code with exec resources. But what exactly does that mean? Here's a definition that you might see in a calculus class.



Oh, the fun things we can write!

boring text

So now we've used Puppet to manage a file on our computer. The /etc/motd file is now owned by root and has a fun little sentence in it. We can write all we want out to that file. But sooner or later, we're going to want to put something a little more interesting. Perhaps we'll want the hostname or operating system installed?

We'll take a little side trip first, though, and learn about $variables.

Puppet Zero

Puppet Zero

Configuration management with tools like Puppet can make your life a lot easier. It can make configuring newly provisioned servers more repeatable and reliable and it can make disaster recovery nearly trivial. Learning to use the tool isn't trivial by any means, though. There are 200 configurable options, give or take depending on the version you're running, and the number of things you can do with it is nearly infinite.

So what is this Puppet thing anyway?

Puppet Zero

So you keep hearing about this Puppet thing and how it's going to solve all of your DevOpsy configuration management problems. But what is it? How do you write a Puppet script? Well, as it turns out, the key concept is unlearning the habit of thinking about scripts. But all in good time. We'll get there. First, let's write some code.

Let's start out with something easy. You all know what the /etc/motd file is. It's the message of the day file that's dumped to your screen every time you log in.