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Configuration management with Chef
Chef de Config
ever dream of rolling out a complete computer farm with a single mouse
click? if you stick to Linux computers and you speak a little Ruby, chef can
go a long way toward making that dream come true. By tim Schürmann
over and making a mess on the server
room floor.
Valuable Ingredients
Chef is basically a server that stores
customized configuration guides for
software. Clients connected to the
server access the recipes and automatically
configure their systems on
the basis of the rulesets the recipes
contain.
To do so, the clients not only modify
their configuration files, but – if
needed – launch their package managers.
If the recipes change, or new
ones are added at a later date, the
clients affected automatically update
to reflect the changes. In an ideal environment,
this just leaves it up to the
administrator to manage the recipes
on the server.
Bulk Shopping
Before you can enjoy the benefits,
the developers behind Chef expect
you to put in a modicum of work. For
example, recipes are made up of one
or multiple standard Ruby scripts. If
you need anything beyond the fairly
generic recipes available on the web,
you need to have a good command of
the Ruby scripting language. In other
words, your mileage will vary before
you deploy a home-grown and hometested
solution.
The installation is another obstacle
– and a fairly complex one, too, because
the Chef server depends on several
other components, each of which
in turn requires even more software
packages. The Chef server itself is
written in Ruby but relies on the RabbitMQ
server and on a Java-based
full-text search engine, at the same
time storing its data in a CouchDB
database.
Finally, your choice of operating system
is also important. Chef prefers
Linux underpinnings, but it will also
run on other Unix-flavored operating
systems such as Mac OS X, Open
Solaris, FreeBSD, and OpenBSD, according
to the wiki [1]. The fastest
approach today is offered by Debian
5, Ubuntu 8.10 or later, or CentOS
5.x. Setting up the server on any
other system can be an adventure.
This article mainly relates to Debian
and Ubuntu for this reason. If this is
the first time you have ever cooked
one of Chef’s recipes, it is also a good
idea to run your kitchen on a virtual
machine. This prevents things boiling
A full-fledged Chef installation comprises
the systems you want to configure
(nodes) and the server that manages
and stores the recipes. Chef clients
do all the hard work, picking up
the recipes from the server via a REST
interface and running the scripts.
Each client runs on one node but can
apply recipes to multiple nodes. [Figure
1] shows you how this works.
For simplicity’s sake, the following
examples just use the Chef server and
a single client. The latter only configures
the computer on which it is running.
The first thing you need to have
in place is Ruby version 1.8.5 through
1.9.2 (with SSL bindings). Add to
this, RubyGems, which will want to
build various extensions and libraries
later on, thus necessitating the existence
of make, gcc, g++, and the Ruby
developer packages. Additionally, you
need the wget tool for various downloads.
The following command installs
the whole enchilada on Debian
and Ubuntu Linux:
sudo apt‐get install ruby U
ruby1.8‐dev libopenssl‐ruby1.8 U
rdoc ri irb build‐essential U
wget ssl‐cert
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