Posts Docker + Ansible

Docker + Ansible

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Again some time without writting. And this time I’m writting about something brand new: Docker.

It lies in the virtualization context. You can read more at docker documentation. And from my point of view, it comes to kill some important challenges me and you have been facing over years when talking about delivering software.


As stated around PaaS often fail to cover every necessity you might have. Because they are closed black boxes where you “commit your code in”, or something like that. I really like heroku and dotCloud, but yes, I have apps that can’t run there.

Ordinary virtualization, another fit for Docker

I’ve been using XenServer to handle massive amount of requests distributed over dozens of machines and it works pretty well. But after using it for a while I have detected some extra “disadvantages” (I’m puting quotes because it is really specific) of this type of virtualization to add to this list. Here they are:

  • The sysadmin should be involved since he needs to access the Xen Center in order to create machines
  • The developer needs to inform beforehand the amount of CPU cores, disk size and memory
  • This involves an all-new machine created with a full operating system, configurations, etc. No time for that!
  • Sysadmins are busy and don’t like to give you attention

Not only that, but many cases crating a full virtualized machine to setup a simple wordpress, or few simple stuff doesn’t pay off. For this sort of situation I’m addopting Docker.

The main advantages of container virtualization (like Docker) are:

  • Platform-as-a-Service like environment. You don’t need to think about anything else but run the process in charge of your application. No worries with an entire machine
  • Make your app immediately available. No boot time needed. Just docker run and you are in
  • Run it over a virtualized Xen machine and you still hold all advantages of XEN in the host level (snapshot, live migration, volume management, etc)

Add to the recipe the idea behind 12 factor apps and you are done! With Docker you can create the folowing workflow:

  1. Developers create a Docker container, commits it to a Docker index or even give you a Dockerfile
  2. Since it is a 12factor app, it is supposed detect resources configuration from the environment it runs
  3. Move your container around development, staging and live envs

Excellent, but still a missing piece.


Ok, call me crazy: “You’ve been using Puppet for more than 1 and a half year, why are you talking about Ansible?. It is simple. Well, Ansible is also simple, but I mean, it is simple to know why Ansible. Just look to step 1 above. See?

Puppet is too much for you to set up your container. Ansible is fine.

You need to be repeatable while setting up containers. You cannot deliver a container with Tomcat 7 plus OpenJDK 1.7 today, and tomorrow deliver Tomcat 6 for the same app. You need consistency archieved through repeatability. Ansible can also give it to you.

Although Docker allows you for commiting images to a repository, you still need to set them up from scratch without forgeting any detail. Otherwise your app wont’t work properly.

Ansible is a direct competitor of Puppet. But with a simpler approach and good enough to run on every server you manage. I tried this combination and approved. Awesome!

The step one above now could be rewritten like:

  1. Developers - with the help of sysadmins or not - create a container and set it up with Ansible. Then commit it to the repository and you can even forget the Dockerfiles (or keep a very minimal one)

I’m absolutely sure Docker will solve many things but bring lots of discussions/patterns about how to solve the problems it is supposed to.


Projects like CoreOS and Flynn literally give you the real notion about what I’m talking. I don’t think PaaS or IaaS will die, absolutely not. But a new room is needed for sure.

I have both Docker and Ansible running production stuff and hope I can share some Playbooks and Dockerfiles in the near future.

This post is licensed under CC BY 4.0 by the author.