chef-Node Attributes and the Precedence Game!

What are Attributes?

Attributes represent information about your node

§ The information can be auto-detected from the

node (e.g. # of CPUs, amount of RAM) &

populated by Ohai

§ You can also set attributes on your node using

cookbook recipes & attribute files, roles,

environments, etc

§ Attributes keep the program code separate from

data

§ All attributes are set on the "node object", and

are indexed for search on the server.

Attribute Sources

Attributes can be set at various levels (in

increasing order of precedence)

− Automagically on the node itself (by Ohai)

− In roles

− In environments

− In cookbook recipes

− In cookbook attribute files

Setting attributes in attribute files

Attributes can be set in the cookbook's

attributes file

− ./cookbooks/<cookbook>/attributes/default.rb

Format is

precedence  attribute name    attribute value

default["apache"]["dir"] = "/etc/apache2"

Setting Attributes in Recipes

They can also be set directly in Recipes

Precede attribute name with 'node.' as

follows

precedence

as a method attribute name attribute value

node.default["apache"]["dir"] = "/etc/apache2"

the node

object

More on attributes - Advanced!

An attribute value can be an array

default["apache"]["listen_ports"] = [ "80","443" ]

 Or it can be a hash

default["apache"]["site1"] = { "port" => 80 }

default["apache"]["site2"] = { "port" => 81 }

8

Never use array attributes

A terrible idea, nipped in the bud

§ An attribute value can be an array

default["apache"]["listen_ports"] = [ "80","443" ]

9

(its a trap)

important point:

It could be a hash. Hashes are great

default["apache"]["site1"] = { "port" => 80 }

default["apache"]["site2"] = { "port" => 81 }

The Problem and the Success Criteria

§ The Problem: We have defined our

'index.html' homepage in the recipe, but we

may want to change that without altering the

recipe

§ Success Criteria: We can change the

homepage by changing an attribute value

Exercise: Set attribute in attributes file

OPEN IN EDITOR: cookbooks/mysite/attributes/default.rb

default['mysite’]['indexfile'] = 'index1.html'

SAVE FILE!

Set an attribute to a specific value in the attributes

file

Exercise: Add index1.html to cookbook’s files/

default directory

OPEN IN EDITOR:

cookbooks/mysite/files/default/index1.html

<html>!

<title>Better Homepage for Gap, Inc.</title>!

<body>!

<h1>Welcome the Gap!</h1>!

<h2>Let’s sell some pants and shirts!</h2>!

<p>We configured this in the attributes file</p>!

</body>!

</html>!

Exercise: Set attribute in a recipe

OPEN IN EDITOR: cookbooks/mysite/recipes/default.rb

service "httpd" do

action [:enable, :start]

end

cookbook_file '/var/www/html/index.html' do

source node['mysite’]['indexfile']

mode '0644'

owner ‘nobody’

group ‘nobody

end

Exercise: Upload the cookbook

knife cookbook upload mysite

Uploading mysite [0.1.0]

Uploaded 1 cookbook.

Exercise: Set attribute in the recipe

OPEN IN EDITOR: cookbooks/mysite/recipes/default.rb

service "httpd" do

action [:enable, :start]

end

node.default[’mysite]['indexfile'] = 'index2.html'

cookbook_file '/var/www/html/index.html' do

source node[’mysite’][’indexfile’]

mode '0644'

owner ‘nobody’

group ‘nobody’

end

Exercise: Add index2.html to cookbook’s files/

default directory

OPEN IN EDITOR:cookbooks/mysite/files/default/index2.html

<html>

<title>Better Homepage for Gap,Inc</title>

<body>

<h1>It is SALE time at Gap!</h1>

<h2>Time for back to school.</h2>

<p>We configured this in the recipe</p>

</body>

</html>

Exercise: Upload the cookbook

knife cookbook upload mysite

Exercise: Viewing attributes using knife

$ knife node show node1 -l | more

...

§ Attributes:

§ tags:

§ Default Attributes:

§ apache:

§ indexfile: index2.html

§ Override Attributes:

§ Automatic Attributes (Ohai Data):

§ block_device:

§ dm-0:

§ removable: 0

§ size: 31563776

§ ...

2

Setting Attributes in Roles and Environments

Attributes can also be set in Roles and

Environments

These use raw JSON or Ruby format

default_attributes({"apache" => {"port" => 80}})