226 lines
11 KiB
ReStructuredText
226 lines
11 KiB
ReStructuredText
FAQ
|
|
===
|
|
|
|
Why Is It Called Ansible?
|
|
-------------------------
|
|
|
|
One of my favorite books is Orson Scott Card's "Ender's Game". In the book, the Ansible is a method of instantaneous
|
|
long distance "hyperspace" communication with a large number of space ships. You should read it!
|
|
|
|
What inspired Ansible?
|
|
----------------------
|
|
|
|
Back when I worked for Red Hat and working on `Cobbler <http://cobbler.github.com/>`_, several of us identified a gap between
|
|
provisioning (Cobbler) and configuration management solutions (cfengine, Puppet, etc).
|
|
There was a need for a way to do ad-hoc tasks efficiently, and various parallel
|
|
SSH scripts were not API based enough for us. So we (Adrian Likins, Seth Vidal, and I)
|
|
created `Func <http://fedorahosted.org/func>`_ -- a secure distributed command framework.
|
|
|
|
I always wanted to have a configuration management system built on Func, but never
|
|
built it due to needing to spend time on Cobbler and other projects.
|
|
In the meantime, a John Eckersberg developed Taboot,
|
|
a deployment framework of sorts that sat on top of Func, using a YAML syntax very
|
|
much like what Ansible now has in :doc:`playbooks`.
|
|
|
|
After trying to get Func running again recently at a new company, I got tired
|
|
of some SSL and DNS issues and decided to create something a bit simpler, taking
|
|
all of the good ideas from Func, and merging them with experience I learned from
|
|
working at Puppet Labs. I wanted something that was easy to pick up and was installable
|
|
without any bootstrapping, and didn't suffer from the "I don't want to learn X" mentality
|
|
that often impacted adoption of tools like Puppet and Chef among certain ops teams.
|
|
|
|
I also spent some time working with a couple of sites that needed to do large webapp deployments,
|
|
and noticed how complex various configuration management and deployment tools were to these
|
|
companies, compared with what they actually needed. Release processes were too complex
|
|
and needed something simple to straighten them out -- but I really didn't want to train
|
|
all the dev(ops) on Puppet or Chef, and they really didn't want to learn them either.
|
|
|
|
I kept thinking, is there a reason for these programs to be so large and complicated?
|
|
Well, systems management is a little complicated, but no. Not really.
|
|
|
|
Can I build something that a sysadmin can
|
|
figure out in 15 minutes and get going, and then extend in any language he knows?
|
|
That's how Ansible was born. It sheds 'best practices' for 'you know your infrastructure
|
|
best', and distills all of the ideas behind all of these other tools to the core.
|
|
|
|
Not only is Ansible very simple and easy to learn/extend, it's configuration management, deployment, and ad-hoc tasks all in one app. And I think that makes it pretty powerful. It hasn't really been done before.
|
|
|
|
I'd like to know what you think of it. Hop by the mailing list and say hi.
|
|
|
|
Comparisons
|
|
-----------
|
|
|
|
vs Func?
|
|
++++++++
|
|
|
|
Ansible uses SSH by default instead of SSL and custom daemons, and requires
|
|
no extra software to run on managed machines. You can also write modules
|
|
in any language as long as they return JSON. Ansible's API, of course, is
|
|
heavily inspired by Func. Ansible also adds
|
|
a configuration management and multinode orchestration layer (:doc:`playbooks`)
|
|
that Func didn't have.
|
|
|
|
vs Puppet?
|
|
++++++++++
|
|
|
|
First off, Ansible wouldn't have happened without Puppet. Puppet took configuration
|
|
management ideas from cfengine and made them sane. However, I still think they can
|
|
be much simpler.
|
|
|
|
Ansible playbooks ARE a complete configuration management system. Unlike Puppet, playbooks
|
|
are implicitly ordered (more like Chef), but still retain the ability to signal
|
|
notification events (like Puppet). This is kind of a 'best of both worlds' thing.
|
|
|
|
There is no central server subject to thundering herd problems, and Ansible is
|
|
also designed with multi-node deployment in mind from day-one -- something that is difficult
|
|
for Puppet because of the pull architecture. Ansible is push based,
|
|
so you can do things in an ordered fashion, addressing batches of servers
|
|
at one time, and you do not have to contend with the dependency graph. It's also extensible in any language
|
|
and the source is designed so that you don't have to be an expert programmer to submit a patch.
|
|
|
|
Ansible's resources are heavily inspired by Puppet, with the "state" keyword being a more or less
|
|
direct port of "ensure" from Puppet. Unlike Puppet, Ansible can be extended in any language,
|
|
even bash ... just return some output in JSON format. You don't need to know Ruby.
|
|
|
|
Unlike Puppet, hosts are taken out of playbooks when they have a failure. It encourages
|
|
'fail first', so you can correct the error, instead of configuring as much of the system
|
|
as it can. A system shouldn't be half correct, especially if we're planning on configuring
|
|
other systems that depend on that system.
|
|
|
|
Ansible also has a VERY short learning curve -- but it also has less language constructs and
|
|
does not create its own programming language. What constructs Ansible does have should be enough to cover 80% or so of the cases of most Puppet users, and it should scale equally well (not having a server is
|
|
almost like cheating).
|
|
|
|
Ansible does support gathering variables from 'facter', if installed, and Ansible templates
|
|
in jinja2 in a way just like Puppet does with erb. Ansible also has it's own facts though,
|
|
so usage of facter is not required to get variables about the system.
|
|
|
|
|
|
vs Chef?
|
|
++++++++
|
|
|
|
Much in the ways Ansible is different from Puppet. Chef is notoriously hard
|
|
to set up on the server, and requires that you know how to program in Ruby to
|
|
use the language. As such, it seems to have a pretty good following mainly
|
|
among Rails coders.
|
|
|
|
Like Chef (and unlike Puppet), Ansible executes configuration tasks in the order
|
|
given, rather than having to manually specify a dependency graph. Ansible extends
|
|
this though, by allowing triggered notifiers, so Apache can, be restarted if needed,
|
|
only once, at the end of a configuration run.
|
|
|
|
Unlike Chef, Ansible's playbooks are not a programming language. This means
|
|
that you can parse Ansible's playbooks and treat the instructions as data. It also
|
|
means working on your infrastructure is not a development task and testing is easier.
|
|
|
|
Ansible can be used regardless of your programming language experience. Both
|
|
Chef and Puppet are around 60k+ lines of code, while Ansible is a much simpler
|
|
program. I believe this strongly leads to more reliable software and a richer
|
|
open source community -- the code is kept simple so it is easy for anyone to
|
|
submit a patch or module.
|
|
|
|
Ansible does support gathering variables from 'ohai', if installed. Ansible also
|
|
has it's own facts so you do not need to use ohai unless you want to.
|
|
|
|
vs Capistrano/Fabric?
|
|
+++++++++++++++++++++
|
|
|
|
These tools aren't really well suited to doing idempotent configuration and are
|
|
typically about pushing software out for web deployment and automating steps.
|
|
|
|
Meanwhile Ansible is designed for other types of configuration management, and contains some
|
|
advanced scaling features.
|
|
|
|
The ansible playbook syntax is documented within one HTML page and also has a MUCH lower learning curve.
|
|
And because Ansible is designed for more than pushing webapps, it's more generally
|
|
useful for sysadmins (not just web developers), and can also be used for firing off ad-hoc tasks.
|
|
|
|
Other Questions
|
|
---------------
|
|
|
|
What is Ansible's approach to security?
|
|
+++++++++++++++++++++++++++++++++++++++
|
|
|
|
Ansible aims to not develop custom daemon or PKI code but rely heavily on OpenSSH, which is extremely well
|
|
peer reviewed and the most widely used security subsystem in the industry. As a result, Ansible
|
|
has a lower attack surface than any configuration management tool featuring daemons that run
|
|
as root, and you do not have to worry about network security vulnerabilities in the tool itself.
|
|
|
|
If your central server is taken over (or even logged into by a malicious employee),
|
|
provided you were using SSH-agent and encrypted keys (and/or sudo with a password),
|
|
your keys are still locked and no one can take control of your nodes.
|
|
|
|
Compared with something like Chef/Puppet/other, compromised manifests would lead
|
|
to a loss of the whole network, with your network turning into an easily controllable
|
|
botnet. Further by not running daemon infrastructure, you have more
|
|
free RAM and compute resources, which should be relevant to users wanting to maximize their
|
|
computing investments.
|
|
|
|
How does Ansible scale?
|
|
+++++++++++++++++++++++
|
|
|
|
Whether in single-execution mode or using ansible playbooks, ansible can
|
|
run multiple commands in seperate parallel forks, thanks to the magic behind
|
|
Python's multiprocessing module.
|
|
|
|
You can decide if you want to try to manage 5 hosts at a time, or 50 at a time.
|
|
It's up to you and how much power you can throw at it and how fast you want
|
|
to go.
|
|
|
|
There are no daemons so it's entirely up to you. When you are aren't using
|
|
Ansible, it is not consuming any resources, and you don't have to contend
|
|
with a herd of machines all knocking at the door of your management server
|
|
all at once.
|
|
|
|
The SSH connection type (paramiko is the default, binary openssh is an option)
|
|
can also make use of "ControlMaster" features in SSH, which reuses network
|
|
connections.
|
|
|
|
If you have 10,000 systems, running a single ansible playbook against all of
|
|
them probably isn't appropriate, which is why ansible-pull exists. This tool
|
|
is designed for running out of git and cron, and can scale to any
|
|
number of hosts. Ansible-pull uses local connections versus SSH, but can be
|
|
easily bootstrapped or reconfigured just using SSH. There is more information
|
|
available about this in the :doc:`playbooks2` section. The self-bootstrapping
|
|
and ease of use are ansible are still retained, even when switching to the pull
|
|
model.
|
|
|
|
If you'd like to discuss scaling strategies further, please hop on the mailing list.
|
|
|
|
Are transports other than SSH supported?
|
|
++++++++++++++++++++++++++++++++++++++++
|
|
|
|
Currently SSH (you can choose between paramiko or the openssh binaries)
|
|
and local connections are supported. The interface is actually pluggable so a
|
|
small patch could bring transport over message bus or XMPP as an option.
|
|
|
|
Stop by the mailing list if you have ideas. The connection-specific parts of Ansible
|
|
are all abstracted away from the core implementation so it is very easy to extend.
|
|
|
|
What are some ideal uses for Ansible?
|
|
+++++++++++++++++++++++++++++++++++++
|
|
|
|
One of the best use cases? Complex multi-node cloud deployments using playbooks. Another good
|
|
example is for configuration management where you
|
|
are starting from a clean OS with no extra software installed, adopting systems
|
|
that are already deployed.
|
|
|
|
Ansible is also great for running ad-hoc tasks across a wide variety of Linux, Unix, and BSDs.
|
|
Because it just uses the basic tools available on the system, it is exceptionally cross platform
|
|
without needing to install management packages on each node.
|
|
|
|
It also excels for writing distributed
|
|
scripts and ad-hoc applications that need to gather data or perform arbitrary
|
|
tasks -- whether for a QA sytem, build system, or anything you can think of.
|
|
|
|
.. seealso::
|
|
|
|
:doc:`examples`
|
|
Examples of basic commands
|
|
:doc:`playbooks`
|
|
Learning ansible's configuration management language
|
|
`Mailing List <http://groups.google.com/group/ansible-project>`_
|
|
Questions? Help? Ideas? Stop by the list on Google Groups
|
|
`irc.freenode.net <http://irc.freenode.net>`_
|
|
#ansible IRC chat channel
|
|
|