All posts by Jesse Keating

OpenStack Nova and Hypervisor disk consumption

Recently I found myself in a situation at $DAYJOB where I needed to account for the local disk consumption of a nova-compute node, a hypervisor. I had a heck of a time gathering all the information I needed to figure out why the space was being consumed the way it was, and since I couldn’t find a single source for all this information I felt it was best to write up a post about it (so that I can find it next time I’m in the same scenario).

This post explores the various ways Nova consumes hypervisor disk space with regard to instance images and booting.

A Nova setup with libvirt/kvm as the hypervisor, ephemeral disk space being provided by a filesystem directory is assumed, and instances booting with ephemeral disk as opposed to Block Storage volumes.

There are two main ways Nova consumes the underlying hypervisor disk space: cached images downloaded from the image service (Glance) and instance ephemeral disk files. All of this content is stored in Nova’s state path, which by default is configured for /var/lib/nova/. In our setup, we mount a filesystem to Nova’s sate path so that we can contain the disk usage to the images and instances that are booted on the system, without risk of filling up / or other critical filesystems.

Image cache

Nova make use of an image cache on each hypervisor. This is a place where each image that’s used to boot an instance is downloaded to and preserved for a period of time. Each time a new instance is created on a hypervisor, the disk cache is checked to see if the image requested for the instance is already in the cache. If it is, that image is used then as the basis for the instance. If not, the image is downloaded from the image store and placed in the cache. This cache is typically on the same filesystem as where Nova stores the instance data (the state path), and thus the images in the cache will account for some amount of overall disk usage and availability for instances. Images in the cache are held for a period of time determined by configuration. Whether to clean unused cache images is a configuration toggle, along with a minimum age for the image before discarding the image.

The amount of space consumed by an image in the cache depends on details from the image itself. While the listed size of the image in the image store may be small, either due to compression or just overall content, the virtual size of the image may be much larger. This virtual size is used as a value to resize the downloaded image to, as Nova will resize each downloaded image to the match the virtual size.

The virtual size of the image depends on how the image was created, the source of the image, and the options used while creating the image. When using the qemu-img tool to create an image, a size can be specified. This will become the virtual size of the image. If creating an image of an existing instance, either by way of an image creation or a backup (which uses the same method), the size of the image will be matched to the size of disk for the flavor the instance uses. If the instance’s flavor states a 200G disk, then the image virtual size from that instance will be 200G, regardless of how little space is actually consumed within the instance.

During an instance creation, Nova downloads an image from glance, checks the virtual size of the image, and resizes the file to the virtual size of the image. This file is saved in an instances/_base/ subdirectory within Nova’s state path. The resize creates a sparse file, where the apparent size matches the virtual size, when the actual consumed size may be much lower. Use of the du utility can show the difference: du -h --apparent-size <file> vs du -h <file>.

Instance ephemeral disk

Each server instance that Nova manages will have its own directory to store data. Part of that data is the ephemeral disk data, the data within the instance itself. The amount of space consumed by the ephemeral disk depends on configuration details of Nova, and on the flavor of the instance.

Copy on write

During an instance creation attempt, Nova will download and resize the base image, if the base image doesn’t already exist. Then Nova may either create a copy on write file for the instance, linked to the base image, or copy the entire base image for the instance with no linkage. This decision is based on a configuration entry, use_cow_images, which defaults to True.

A copy on write file is an overlay file that will overlay on top of the base image file and keep track of any changes to the filesystem within the image.

If copy on write is desired, overlays are created from the base image to the instances/<uuid>/disk file within the state path. Otherwise a direct copy will be made to the same path.


In either case, Nova may make a call to pre-allocate enough blocks on that file to be able to fill the size of the flavor’s disk. This is determined by a configuration entry preallocate_image.

If copy on write is used then the file will appear one of two ways. Without image preallocation, the file will only be as large as the amount of change that has occurred in the file since boot, thus it can be quite small to start with, but may expand to the full size of the flavor’s disk size. With image preallocation set, both the apparent and actual size will be the full size of the flavor’s disk size.

If a direct copy of the image file is used, then the file will appear in one of two ways. Without image preallocation, then the file will appear exactly as it does in the image cache. The apparent size will can be quite large, but the actual size will be relatively smaller. With image preallocation, both the apparent and the actual size will be the full size of the flavor’s disk size.


Qemu will be launched referencing the disk file in instances/<uuid>/, which may or may not be linked to the cached image file. This linkage is what determines whether or not an image file in the cache is still “in use”, and will prevent Nova from removing the file when it ages out.


The amount of disk space consumed on a hypervisor depends on numerous factors, such as source image virtual size, the number of active unique images used to boot instances on the hypervisor, and configuration settings regarding disk preallocation and copy on write files. The vast majority of overall consumption of space by Nova will be the sum of all the cached images and all the ephemeral disks for all the instances booted on a given hypervisor.

Configuration items that drive decisions

  • preallocate_disk: Can set to none or space. If space, an fallocate call is made on the instance (overlay) disk to allocate enough blocks to cover the flavor disk size. Without preallocating, the underlying hypervisor filesystem can become overcommitted, and if an instance causes enough data change to occur to it’s disk file, the host filesystem may become exhausted. An operator could prevent exhaustion by relying on the DiskFilter scheduling filter to avoid scheduling instances to where disk has been fully committed, but there are defects and drawbacks to this filter (a subject for a future post). The default value is none
  • use_cow_images: Can be set to True or False. If True, the instance’s disk file is a copy on write file, attached to the base image in nova’s image cache (instances/_base/). When this happens, the base image for any booted instance is always held open, and cannot be cleaned. This can drive up the storage overhead on a hypervisor. The default value is True.
  • remove_unused_base_images: Can be set to True or False. If True, when a cached image is no longer used by an instance on the hypervisor, and has reached a minimum age, the image will be removed from the cache. This can prevent unbound growth of the image cache on a hypervisor. The default is True.
  • remove_unused_original_minimum_age_seconds: An integer of seconds to indicate how old an image file must be before it is a candidate for removal if unused. The default value is 86400.

Why I love open source!

The other day I decided it was time I got familiar with Docker. Yes, I know, I’m a bit late to the party, but better late than never. I understood some of the concepts around Docker, just not necessarily the mechanics, so it was time to dive in.

Docker these days has a handy utility named docker-machine. This tool is used to create a target system to create docker containers on. This is really useful if you’re on a Mac and don’t have a kernel that supports containers natively. By using docker-machine I was able to provision a VM via VirtualBox that was all set up to run containers. From that point in, docker commands ran as expected, and containers showed up inside the VirtualBox VM.

This is all well and good, but being a curious nerd I wanted to see what other drivers there were for docker-machine. Unsurprisingly, there are numerous drivers, many of them cloud based. There is an OpenStack driver as well, which is great! My day job is all about OpenStack and I have numerous clouds at my disposal. The idea of utilizing my cloud to run docker containers just seems natural to me, so that’s what I tried to do.

Unfortunately I ran into a problem. Our clouds work in a way that requires the allocation of a “floating IP” address to an instance in order for that instance to be accessible by the outside world. The docker-machine OpenStack driver supports this, by passing in the correct arguments to tell the driver where to allocate the floating IP from, a pool. It turns out that my account on the cloud I was targeting has admin level rights (a scenario many of my customers will be in), and thus was able to see more available floating IP addresses in the pool than a normal user would, many of which had been allocated to a different project (projects, or tenants in OpenStack are a way to segregate groups of users and resources within a cloud). The docker-machine driver simply attempted to use the first address it thought was available for the instance it just created. In my case, this address had already been allocated to a different tenant and the OpenStack API returned an error when the assignment to my instance was attempted.

I understood the problem, and I had a general idea of how to fix it. The driver should filter the floating IP addresses by my project ID when searching for an available floating IP to use. I essentially had three choices at this point:
Door #1: If the project didn’t have a public bug tracker I could give up on the tool or write a negative review somewhere or a snarky tweet about it and find something else to play with.
Door #2: If the project had a public bug tracker I could file a bug in the tracker and explain the scenario that led to the error. I would just have to wait and hope somebody at the project cared enough to fix my bug.
Door #3:Because docker-machine is an open source project, I had a third choice. I could pull down the code and try my hand at fixing the problem myself.

Obviously I went with door #3. I’ve never looked at the source code behind Docker before (written in Go), but I figured I could fudge my way through a small change. Thankfully the Docker project has spent a fair amount of time thinking about how to make contributing to the project an easy process. Numerous documents exist to help guide a first time contributor through setting up a development environment, understanding the code testing tools, and walking through the submission and review process. Following these guides I was able to start making modifications to the docker-machine code and testing them out on my laptop. What I thought was going to be a simple change turned out to be a more involved code addition, which led me to reading the code and developer documents for a supporting library that docker-machine uses.

Through much iteration and testing, I was finally able to create a change that resolved my issue in a satisfactory way. Being a good open source citizen, I then submitted this change back up to the project in hopes of inclusion in a future release. I myself am not currently blocked in using this tool, but I’d like my customers to be able to use this tool as well, in a way that doesn’t require me to distribute a modified binary to them.

This is the real joy of Open Source to me. I found a tool I want to make use of, I discovered a way in which the tool doesn’t quite work right for me, I have access to the code to debug the problem, I have access to the documentation and supporting code to develop a solution, and I have the opportunity to contribute a change back to the tool. This process feels so natural to me now that any other way just seems broken. Open Source has enabled me to make my life better, as well as potentially making the life of other users of the software better too, and that gets me right in the feels.

To Do Journaling


A co-worker noticed me taking some notes in my notebook the other day, and asked about my To Do journaling (yes I’m making that word up). There was genuine interest from a few other people, so I decided to make a blog post about it.

To Do journaling, to me, is writing down a list of things to accomplish for the day. This is a pretty common practice, and there is nothing really revelatory about the process, simply write the things you want to do down. I started doing this when I couldn’t keep track of the things I needed to do in my head any more, and I was letting things fall through the crack. There are many ways in which one could enumerate a to do list; there is a whole industry around tools to help one accomplish this. However, given how much of my life is ruled by electronic means and apps and tools, I have eschewed the “smart” tools, and instead have adopted a more traditional model. I find it helps keep me grounded.

For my journaling, I prefer to use pen and paper. A physical notebook I carry with me in which I can document my to dos for the day, and any sort of notes I need to write down. Writing things down by hand seems to trigger some bit of memory goo in my brain and helps me to remember it. If I type it out, it seems to slip through the synapses and fall out the other side, but writing it down gives it a bit of “stickiness”. Because I will spend a fair amount of time touching and feeling and writing in my notebook, I splurge on a high quality notebook. One that’s the right size, the right paper feel, and a nice cover. My current favorite is the Rhodia Webnotebook, in black. This notebook is hardcover, which helps me write on a variety of surfaces, but it covered in a very comfortable leatherette. The paper is very nice as well. A good notebook deserves a good pen too. I’ve gone through a multitude of pens in the past, with various favorites along the way. My current favorite is the Sharpie Grip Pen with a fine black point. These aren’t super fancy, but they write nicely (particularly on the Rhodia paper) and feel good in the hand. Additionally they’re so cheap that I don’t fret if I lose one. To keep my pen and my note pad together, I got a Quiver pen holder. This actually cost more than the notebook and pens combined, but unlike the notebook and pen which are consumables, the Quiver will transfer from note book to note book. This keeps my pen always with my notebook, and adds a nice touch of style to the setup.

Enough about the gear, lets talk about the process. Every day I create a new to do list. Every day is a fresh list, so that I don’t have to keep paging back through history to find the list of things to do. I make a To Do XX/XX header to indicate the date, and then start listing things prefixed with a dash.


This is just a simple, unordered list. I typically leave room to the right of the list so that later, after taking various notes below it, if I need to add another item I have room. Having the items unordered also means I don’t stress if I have to add an item later, it can go wherever and not upset any ordering. As I start working on something, I’ll make a tilde mark next to the list item.


Later, as I finish an item, I’ll check it off with a check mark. I do not cross the item out, because I want to be able to go back through my history to remember the things I’ve done. Crossing an item out makes it that much harder to read (my handwriting is challenging enough).


If at the end of the day I haven’t accomplished everything on my list, I draw a square around the incomplete items. This square is a visual cue that lets me know I need to carry the item over into the next day’s list. In this way I don’t lost track of the things I want to accomplish, but I don’t have to flip back to previous days. I just carry over the unfinished items to the next day.


This very simple process has kept me on top of the things I need to accomplish for the past few years. I’ve filled a number of notebooks this way, and that feels like a great accomplishment. Every time I feel like nothing is happening and my wheels are spinning I can page through them and realize that yes, I am actually getting things done. This process also helps come review time, looking back at past accomplishments. I haven’t done this yet, but I could star the items that would be good to highlight in any future self review scenario.

Thanks for reading, and feel free to share your own to do process in the comments, or on twitter.

Ansible copying content from one remote system to another

Just a quick tip of you’re trying to do the same thing I was trying to do.

The Problem

I am generating some content on Server A. I want to replicate this content onto Servers B and C.

The Solution

TL;DR: Read files content from Server A. Write files on Servers B and C from those contents.

Ansible provides a couple modules that make this possible. The first one we’ll look at is the slurp module. This module allows you to read in contents of a file from a remote system. Here is an task to read the content, utilizing the run_once mechanism:

This will read each of those files in and save the results in the pki_certs variable. Ansible will only do this once, presumably on the host where this content was generated with a previous run_once task. However the variable data will be assigned to every host to make it easily accessible.

Next we need to write out the content on our other systems. There are a couple things to consider. First, because the files were read via a with_items loop, the registered content is in a list, specifically in pki_certs.results. This is easy enough to deal with because the results list is a list of dictionaries, and the name of the file is part of that dictionary. The filename resides in the item key, while the content resides in the content key. This allows us to template out both the path to be written as well as the content to be written at that path.

The next thing we need to consider is that the slurp module stores content in base 64 encoding. That means when we write it back out, we need to decode it from base 64, otherwise Ansible will happily write out some long strings that look nothing like your file. To decode from base 64, simply use the b64decode filter on the content variable.

The last thing to consider has to do with yaml and whitespace and ansible. This may not come into play with every file, but these files have multiple lines. A somewhat recent change in Ansible means that if the “short form” of task description is used (with key=value parameters) your written out file will have double linefeeds. The simple solution is to use “long form” task syntax as you’ll see below:

Because every host has access to the pki_certs variable this task can run across all of them. You might see a change registered for the first host in the loop, even though it was the source of the content, due to permissions or ownership changes, however subsequent runs will be nice and clean.

Hopefully this helps you out and saves you from spending an afternoon poking around at it like I just did!

On next chapters

I haven’t gotten a lot of sleep lately, I’ve had quite a lot on my mind.

I’ve been a “Racker” for almost two years now. I’ve helped build an amazing thing. The way we expand, deploy, upgrade, operate, and otherwise manipulate OpenStack and  the other infrastructure behind the Rackspace Public Cloud is awesome, and getting better all the time. As much as I would love to stay on and continue to intensify the awesomeness, it was time to say good bye. While I’ve done a lot of the work, I wasn’t the only one, and I know that there are a lot of good people still plugged into the mission and it will go on.

What’s next? Well, I’ve been a working remotely for over 6 years now. It has been fantastic to be able to be home and around my family as we’ve grown. I’ve tried hard to strike a balance between work travels and home life, but sometimes that balance falls out of whack, particularly when the social side of me that craves in person interaction overrules the empathy side of me that keeps me in check when I’m putting too much on the shoulders of those I leave behind. With our boys growing older, spending quality time with them is more important than ever, which is making it harder and harder to make frequent visits to my Rackspace offices. At the same time, my boys are both now in full time school, which opens up my day time hours, which means it’s a great time to think about re-joining the “work from office” folks. I’ve also been working for large publicly traded companies for nearly 10 years, and I really felt like it was time to get back into the small startup game.

I’m very excited to be joining the Blue Box team as an OpenStack Engineer. I get to keep working on OpenStack stuff, and Ansible stuff, and other fun open source things. They’re in Seattle, which gives me an excuse to get on my bike a few days a week and multi-modal commute in, and still strike a good balance with my home life. I also get to plug more firmly into the Seattle tech scene, which exploded with awesomeness since I was last a part of it.

Parting ways is never easy, but the relationships I’ve built feel strong enough to survive. We’ll still see each other at various conferences and meet ups, and we’ll all keep working to make OpenStack even better.

Persistent SSH connections with context!

SSH, the Secure Shell, is an awesome tool. Rather indispensable for somebody like me who has to operate on remote systems. I use it constantly to either run code from a privileged host or log into systems to diagnose problems. My entire cloud of servers is just a terminal session away.

I’m also a huge fan of laptops. I really like being portable with my computer. Partly because I work from home, which means I often work from a coffee shop, or various parts of my home. I don’t have a “workstation” that I’m tied to, and I haven’t for years. I fell in love with the ease in just closing up my laptop and walking outside, or riding my bike to the cafe and opening it back up to continue work right where I left off.

Unfortunately, over time, the ease of transport has lessened, and for good reasons. First up is the VPN, or Virtual Private Network. VPNs allow me as a remote person to securely log into my employer’s network in order to access resources, or SSH into systems. VPNs are ubiquitous now for remote workers. In the good days, my VPN was automatic. If I closed my laptop and relocated within my house, upon opening my laptop the VPN would re-establish itself without my interaction. SSH, with it’s built in ability to re-establish communication would often come back fine, and whatever I was working on, i.e. my context, would be saved. But as time went on, automatic VPNs began to be viewed as insecure. They required stored credentials on my laptop, and it mean that whomever had my laptop had access to these credentials. To combat this, VPNs started using “One Time Passwords“, or OTPs. OTPs come in many flavors, but essentially they combine a Thing You Have (like a number generating physical device) with a Thing You Know (a passphrase only you know) into a unique string of characters. The numbers from the device plus your passphrase. This combo could be used only once to authenticate and after that it was invalid. More secure, but this ended the days of automatically established VPNs, and it often meant that the time it took me to re-establish my VPN went beyond SSH’s ability to recover a connection. Because of this I’d often find myself walking around my house with my laptop open rather than closed, to keep my connections running. Not nearly as cool and convenient of just closing it and walking around.

Of course, this doesn’t consider transitions from my home to a coffee shop. Two problems there, length of time to get to my destination exceeds SSH recovery time, and the local network details will have changed, preventing SSH recovery completely. This means whenever I go somewhere not my home, I have to re-establish my SSH session(s) and recover my context.

Keeping context is a solved problem. There are tools out there that help with this. GNU Screen and Tmux are very popular options. These utilities essentially create a terminal session that is insulated from disconnections. When you reconnect to wherever a screen or tmux session is running, you can re-attach to the session and all your context is back. These tools have been around for a while and work really well, when you remember to do your work inside one of them. However getting to them is still a manual process. I have to wait for my SSH session to finally realize it can’t re-establish my connection, then I have to re-issue the SSH connection command on my local laptop, and once connected I have to re-attach to whatever session I was working on. Not a lot of work, but certainly an annoyance.

What I want is something that will keep my SSH connections persistent. Persistent across network outages or even network relocations. Not only do I want the connection itself persistent, but I want the context within that connection to be persistent as well. I don’t just want my ssh connection to re-establish itself should it timeout, I want to be re-attached to whatever session I was working in.

Thankfully there are a few tools out there that help with this! Mosh and autossh.

Mosh is kind of the new kid on the block, and is rather interesting. It does a few more things than just keep a persistent connection with context. It also does some things which really help with performance (perceived and actual) over slow connections. When you start a mosh session, it uses ssh to connect to the target and starts some software there, software that your local mosh client will use to communicate with. When the network dies or changes, mosh will quickly re-establish communication with the remote software and your terminal acts as if nothing has changed.

I played around a bit with mosh when it first came out and discovered some things I didn’t like about the setup. First, mosh requires new software be installed on  your connection target. This can either be extremely easy, or a nightmare depending on the target, corporate policy, etc… The other thing I really didn’t like about mosh is what it does to your local terminal window. I currently use OSX as my operating system, and within it I use iTerm2 as my terminal emulator. Often I use the built in search function of iTerm2 to find things in scrollback, or I just simply use the touchpad to scroll back my iTerm2 window to read things that have “scrolled off” my screen. These things are quick and natural and useful. Unfortunately the way mosh works, neither of those things are possible. Scrolling back will only show you the things on your terminal from BEFORE you started your mosh session. All that has happened within your mosh session and has scrolled off your screen is lost. Mosh says to use screen or tmux to capture that, and use the scrollback capability of screen or tmux to review or search it. Because of these reasons, I don’t use mosh, although I will say it is really neat, and does feel extremely fast. If I worked more on very laggy connections I may feel different about it.

The other option I mentioned is AutoSSH. AutoSSH is similar to mosh, in that it attempts to re-establish a broken connection, but it is different in a few key ways. First, it’s a pure ssh implementation. It does not require additional software to be installed on the remote host, and it does not attempt any communication over anything other than ssh. It does not however attempt to keep context. All it will do by itself is re-establish an ssh connection to a given remote host. In order to retain context, screen or tmux are needed. Thankfully it is trivial to use screen or tmux in a way that automatically (re)connects to a session. In my case, I use screen. Screen has one important feature over Tmux for me, and that feature is the way it does scrollback. When using screen in a iTerm2 window, anything that scrolls off the screen is still in the “history” of iTerm2, which means I can scroll up with the touch pad, or use iTerm2’s search feature to find things. This does not work when using Tmux, so I have gone with screen.

Screen has the ability to with one action either create a new session, or if the session named already exists, disconnect that session from wherever it may be connected and reconnect it to where you are now. That is accomplished via $ screen -D -R session_name  . This can be added to an execution of autossh, so that when autossh initially establishes your connection, or ever re-establishes your connection, the execution will run:

This is nearly perfect, but it doesn’t seem to react as fast as mosh does to network disconnects and reconnects. This is due to some defaults in autossh, namely how frequently it polls the monitoring port for activity. The default poll time is 600 seconds, which can be quite a long time. I’ve found that a poll time of 5 seconds seems to keep things feeling fast. To adjust this, it’s as simple as adding an environment variable when launching autossh. Also due to a bug one needs to also adjust the time autossh will wait to first start polling a connection.

Now autossh will start monitoring my connection after 5 seconds, and monitor it every 5 seconds for changes. When it reconnects, it will automatically reattach my screen session for context. Any scrollback is still in my terminal window so my local native terminal actions still work, which means I can roam at will without losing my work! Granted, this does require that screen is installed on the remote host, but screen is nearly ubiquitous these days, and hardly ever contentious to get installed if it isn’t already on your remote host.

This setup has made my life more awesome, and I hope it will make your life more awesome too, dear reader. If you have anything to add, or other tricks for this style of work life you’d like to share, please use the comments boxes. They require my approval but I’ll get to them quite quickly!

SSH Key Rotation with Ansible

Introduction to SSH Keys

SSH keys are fantastic things. They provide a 2-part blob of data, a private part and a public part, that can be used to authenticate ssh connections. You keep the private part private, often with a passphrase to “unlock” it, while you can hand out the public part to things like GitHub, compute cloudsother systems that you might wish to connect to via SSH, and remote servers you will ssh to. The public part of your SSH key pair gets stored in a special file that SSH servers on remote systems read, the authorized_keys file. When you connect, your ssh client will provide details about your private key that the remote end can validate against your public key to authenticate you. This is a great convenience over having to provide a password every single time.

This convenience for users is also a necessity for infrastructure administration. SSH is ubiquitous in the Linux world, and the vast majority of administration is accomplished over SSH. Without the ability to use SSH Keys (or similar auth mechanisms) one would not be able to automate actions across many systems easily.

With convenience comes responsibility though. Having a key that an automated process can use to manipulate your fleet of systems is great, but it’s also a pretty juicy attack vector. For that reason it is good practice to rotate your keys often. Rotating keys is the act of replacing the keys you’re currently using with new keys, and removing the ability for old keys to be used to log into your systems.

Rotating keys requires a new key. Creating a new key is fairly simple. Getting the public part of this key out into your fleet, and removing existing public keys is a bit harder. Thankfully we have orchestration and automation tools such as Ansible. The rest of this blog post will discuss how to use Ansible to automate rotating your ssh credentials across your fleet.

Orchestrating SSH Key Rotation

Lets consider the steps necessary to rotate a key:

  1. Create a new key
  2. Add new key to authorized_keys files on your fleet
  3. Test new key
  4. Remove previous keys from authorized_keys files

As stated before, step 1 is simple, and for the sake of this post we’ll assume that this has been completed, and there is a new key-pair, located at ~/.ssh/id_rsa_new and ~/.ssh/ The private key part is id_rsa_new, the public is It’s the pub we need to distribute. For now, we’ll also assume that this key has not yet replaced the existing key, and we can still use the existing key to reach our fleet.

Step 2 is adding the new key to the authorized_keys file. This is where our Ansible playbook will begin. First we need a play header and a couple variables defined to reference the public and private parts of our new key-pair.

Next we’ll need a task to copy the public part of our new key-pair to the remote hosts. For this we will use the authorized_key module. This module allows us to provide a key to add, which we will do.

Now for step 3, we will want to test this new key, to make sure that our new key addition is working. To do this, we will need to direct Ansible to use our new private key when connecting to our servers. We can use a set_fact task to set ansible_ssh_private_key variable to our new private key.

Our next task will make use of this new key when creating the connection (provided ControlPersist is not at play).

The next task is step 4, removing previous keys. Because of our previous task, this step will make use of the new key, and accomplish step 3 along the way.

Currently, the authorized_key Ansible module does not have a method to remove all but the specified ssh key. However I have sent a pull request to accomplish this, by way of the exclusive keyword. The task here will assume that this pull request has merged.

This task looks just like the first task, but with the addition of exclusive=yes. If you don’t want to use the modified authorized_key module, you could make use of the copy module which could get content from the new_pub_key file similar to how authorized_key gets content from the file.

If all has gone well, all that should be left in the authorized_keys file is the public part of our new key-pair. Our new key has been successfully rotated in and the old key is no longer allowed to log in.

Next Steps

There are more things we could do with our playbook. We could automate the creation of the key itself, which would look something like this:

The when conditional here makes sure that only one key is generated, by only running on the first  host. Delegation is also used to make the action happen on the system calling ansible, rather than a remote host.

We could also move the private key file into a location that our local ssh config is prepared to use by default:

Any number of other tasks could be added around these, or specific options to the existing tasks. This blog post is just enough to get you started.


SSH keys are awesome. Anybody using ssh should be using keys. Keys are powerful, and thus need care. Rotate keys frequently and make sure to invalidate old keys. Automation can make this process a lot easier and more reliable.

For convenience, here is a complete playbook code block:

And lastly here is a horn-less unicorn pooping a rainbow I found on photobucket, because this post has been far too serious.


Breaking the cycle – It’s okay to say “I don’t know”.

While listening to a recent Freakonomics podcast, I learned that from childhood on there is programming to teach us that it is better to have an answer, even if it is wrong, than to not have an answer at all. Why this happens is not fully understood, but the consequences are becoming more apparent. Maybe my upbringing was different, but I’ve never seemed to have a problem with stating that “I don’t know”. But I have ran into people who always seem to have the answer, even if it is wrong.

People in the business world are no exception. There often can be an expectation set, particularly for people in more senior positions, to be experts in our fields, which to some means always having an answer.

Far too often though, we don’t have an answer. Our skill isn’t in knowing all the answers, our skill is in being able to discover the answer. It’s knowing when to ask for help, where to get that help, and how to sort through data to find a solution.

Stating that “I don’t know” is not an admittance of failure. Instead it is an invitation for collaboration and discovery. It is the very nature of science and the Scientific Method; starting with an unknown, research to form a hypothesis, test that hypothesis by experimentation, analyze the data and form a conclusion, then communicate the results. Science works when we start with the unknown and journey to the known. The door is open for others to provide ideas and research to the table. Differing opinions are welcome and debated.

When we skip passed the “I don’t know” stage and jump straight to an answer, particularly when practicing “fake it until you make it”, any differing opinion is viewed as adversarial. This creates conflict rather than collaboration. More effort will be spent to entrench on the wrong answer just to hold up the illusion that one has all the answers. Any evidence that does not support the already chosen answer will be ignored or discounted.

In these situations, a wrong answer asserted with authority, is far more expensive than the answer of “I don’t know” and the subsequent period of discovery. Good money and time will be thrown after bad, just to make the wrong answer work, or to find ways to blame other things from preventing the wrong answer from working. This creates a very hostile work environment and does not foster collaboration.

Speaking of discovery, the only method to to learn new things is through feedback. Feedback often comes from the process of trail and error, or experimentation. When it is okay to be wrong, it is also okay to make mistakes and errors. This leads to much clearer data and better understanding of the problem at hand. The ability and encouragement to try new things, even if (and especially if) they fail is a fantastic tool for learning, and ultimately for discovering the best answers to a given question.

In many ways, the ability to admit not knowing the answer to something is a valuable trait, one that should be celebrated, encouraged, and cultivated. An environment should be created and maintained that fosters this behavior. Encourage trail and error. Celebrate failures as data about what doesn’t work and use it as data to measure what does work against. The rewards will be many.

I won’t claim that this is the best way, I just don’t know. What I do know is that organizations I’ve been a part of that have embraced the culture of discovery have been more successful and more pleasant to be a part of than those which haven’t. I encourage those I work with to not be afraid to state “I don’t know”. It’s impossible to know everything about everything. Together we work to find answers to the unknown and the journey is just as important as the solution.

Hosting my own blog

Many moons ago I had a LiveJournal blog. At the time I just didn’t want to be bothered with hosting my own stuff, and there was a LiveJournal community. Many of my peers also used LiveJournal, so I followed the herd.

Fast forward a few years and I blogged less and less, as I joined social media and participated in things like Facebook more and more. My LiveJournal basically stopped in 2010.

In April of 2012, I moved to the Anaconda team at Red Hat to be a full time developer on the installer software, and I decided to start blogging about that. LiveJournal felt clunky so I wanted something new and cool, and I was terrified of running my own blog software, so I got a account and started publishing. Shortly after that I left Red Hat and joined Rackspace, and gave the blog a new title.

Now that I’m at Rackspace working on our Public Cloud, it seems really silly to keep hosting a blog on blogspot. So I’ve bit the bullet as it were and created a wordpress site to keep my blogging going. I don’t know what I’ll post about, or how often I’ll do it, or if anybody will care, but it will be therapeutic to me at least, and that’s all that really matters.

Linuxfest Northwest 2013

Time flies, and another LFNW is upon us. I haven’t fully decompressed from attending my first OpenStack Summit but now I have to switch gears and get ready for LFNW.

This year I’m giving 3 presentations, one of which is a 80 minute session that I’m sharing with a good friend — a repeat of a popular session we did last year. Here is a link to the sessions:

LFNW is a free event with good quality sessions given by good quality people. The “hallway track” is just as valuable as the other tracks as you can build lasting relationships with the tech movers and shakers of the area.

This will be something like my 10th year going. I hope to see some of you there too!