ansible/README.md

Ansible
=======

Ansible is a extra-simple tool/API for doing 'parallel remote things' over SSH -- whether
executing commands, running declarative 'modules', or executing larger 'playbooks' that 
can serve as a configuration management or deployment system.

While [Func](http://fedorahosted.org/func), which I co-wrote, 
aspired to avoid using SSH and have it's own daemon infrastructure, 
Ansible aspires to be quite different and more minimal, but still able 
to grow more modularly over time.  This is based on talking to a lot of 
users of various tools and wishing to eliminate problems with connectivity 
and long running daemons, or not picking tool X because they preferred to 
code in Y.

Why use Ansible versus something else?  (Fabric, Capistrano, mCollective, 
Func, SaltStack, etc?) It will have far less code, it will be more correct, 
and it will be the easiest thing to hack on and use you'll ever see -- 
regardless of your favorite language of choice.  Want to only code plugins 
in bash or clojure?  Ansible doesn't care.  The docs will fit on one page 
and the source will be blindingly obvious.

Design Principles
=================

    * Dead simple setup
    * Super fast & parallel by default
    * No server or client daemons, uses existing SSHd
    * No additional software required on client boxes
    * Everything is self updating on the clients  
    * Plugins can be written in ANY language
    * API usage is an equal citizen to CLI usage
    * Can be controlled/installed/used as non-root

Requirements
============

For the server the tool is running from, *only*:

    * python 2.6 -- or the 2.4/2.5 backport of the multiprocessing module
    * PyYAML (install on 'overlord' if using playbooks)
    * paramiko

Optional -- If you want to push templates, the nodes need:

    * python-jinja2 

Inventory file
==============

To use ansible you must have a list of hosts somewhere.

The default inventory file (-H) is /etc/ansible/hosts and is a list
of all hostnames to manage with ansible, one per line.  These
can be hostnames or IPs

Example:

    abc.example.com
    def.example.com
    192.168.10.50
    192.168.10.51

This list is further filtered by the pattern wildcard (-P) to target
specific hosts.  This is covered below.

You can organize groups of systems by having multiple inventory
files (i.e. keeping webservers different from dbservers, etc)

Massive Parallelism, Pattern Matching, and a Usage Example
==========================================================

Reboot all web servers in Atlanta, 10 at a time:
 
   * ssh-agent bash
   * ssh-add ~/.ssh/id_rsa.pub
   * ansible -p "atlanta-web*" -f 10 -n command -a "/sbin/reboot"

File Transfer
=============

Ansible can SCP lots of files to lots of places in parallel.

   * ansible -p "web-*.acme.net" -f 10 -n copy -a "/etc/hosts /tmp/hosts"

Templating
==========

JSON files can be placed for template metadata using Jinja2.  Variables
placed by 'setup' can be reused between ansible runs.

   * ansible -p "*" -n setup -a "ntp_server=192.168.1.1"
   * ansible -p "*" -n template /srv/motd.j2 /etc/motd 
   * ansible -p "*" -n template /srv/foo.j2 /etc/foo

Git Deployments
===============

Deploy your webapp straight from git

  * ansible -p "web*" -n git -a "repo=git://foo dest=/srv/myapp version=HEAD"

Take Inventory
==============

Run popular open-source data discovery tools across a wide number of hosts.
This is best used from API scripts.

  * ansible -p "dbserver*" -n facter
  * ansible -p "dbserver"" -n ohai

Other Modules
=============

See the library directory for lots of extras.  There's also a manpage,
ansible-modules(5).

Playbooks
=========

Playbooks are particularly awesome.  Playbooks can batch ansible commands
together, and can even fire off triggers when certain commands report changes.
They are the basis for a really simple configuration management system, unlike
any that already exist.  Powerful, concise, but dead simple.

See examples/playbook.yml for what the syntax looks like.

To run a playbook:

ansible -r playbook.yml

Read ansible-playbook(5) for more details.

Future plans
============

   * see github's issue tracker for what we're thinking about

License
=======

   * MIT

Mailing List
============

   * Join the mailing list to talk about Ansible!
   * [ansible-project](http://groups.google.com/group/ansible-project)

Author
======

Michael DeHaan -- michael.dehaan@gmail.com

[http://michaeldehaan.net](http://michaeldehaan.net/)