Learning Ansible: KVM Deployment Use Case

"Pioneers get shot in the back", is what Stan Sigmund (do I have that spelled right?), the CEO of at&t used to say. Well, I don't know this firsthand. This is what some at&t employees told me once.

But it's true. It's always a lot safer to go in after the initial wave of invaders have taken all of the risk, and I think that's what Stan would have been referring to with that statement. It's about risk, which is a topic in an of itself, very blogworthy.

How does this relate to Ansible?

We have an engineer here who likes to run out in front of the curve. He did all of this research on Puppet, Chef, and Ansible, and chose Ansible. There are any number of blogs that tout the benefits of Ansible over these others, but in order to fully grasp those benefits, you need to study them all.

For me, I need to learn by doing, and then I can start to understand the benefits of one vs another.

So, I have started by taking a number of playbooks, and trying to get them working on my own system. I built a KVM host environment on a 32Gb server, and it made sense to see what I could do in terms of trying to automate the generation and spinup of these Virtual Machines.

There are a number of new things I have come across as I have been doing this:

1. Guestfish - Guestfish is a shell and command-line tool for examining and modifying virtual machine filesystems.

http://libguestfs.org/guestfish.1.html

2. getent - a small IP / host resolver that is written in Python.

https://pypi.python.org/pypi/getent

The scripts I am using are all set up to create a virtual machine using some defaults:
- default storage pool
- default network

Certainly this is easier to do than creating one-offs for every VM. But if you do this, you need to go into virt-manager and reprovision the networking and other things individually. Which kinds of defeats the purpose of using ansible in the first place (you can use a bash deploy script to generate a KVM).

So one of the things I did have to do was to hack the scripts to work with the storage pool I was using, which placed all of the images in MY directory, as opposed to where the default images were being placed.

Somehow, I need to enhance these scripts to put each VM on its own network subnet. This can all be done with virsh commands and variables, but I have not done that yet.

One problem, is that you need a MAC address to assign your adaptors if you're going to try and create those dynamically. I looked, and came across this link that can possibly serve as a weapon for doing this:

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/5/html/Virtualization/sect-Virtualization-Tips_and_tricks-Generating_a_new_unique_MAC_address.html

I have a handle on Ansible now; what a Playbook is, the Inventory File, what Tasks are, Roles are, Handlers, and the like. I understand all this, but can I swiftly and efficiently code all of this? No - not yet. I'm still reverse-engineer hacking from existing stuff. The background as an Integrator has honed those skills pretty well.

Ansible is as good as the underlying inputs that are fed into the process of generating outputs. It can be simple. It can be complicated. My impression is that it makes sense to crank it initially, and then enhance and hone over a period of time. Trying to everything up front and in one shot will be a huge time sink.

I'll probably write more about Ansible later. This is all for now.