Recipes, Resources & Cookbooks

Resources — Declarative Building Blocks

A resource describes desired state, not the steps to get there. Chef's providers figure out the actual commands for the specific OS/package manager.

package 'nginx' do
  action :install
end

template '/etc/nginx/nginx.conf' do
  source 'nginx.conf.erb'
  variables(port: node['nginx']['port'])
  notifies :restart, 'service[nginx]'   # only restarts if the file actually changed
end

service 'nginx' do
  action [:enable, :start]
end

Idempotency

Running the same recipe repeatedly produces the same result with no errors — package 'nginx' do action :install end does nothing if nginx is already installed. This lets Chef Client run on a schedule without breaking an already-converged system.

Cookbook Structure

my_cookbook/
  recipes/default.rb
  attributes/default.rb
  templates/nginx.conf.erb
  files/
  metadata.rb

# Chef Supermarket — public repo of shareable community cookbooks,
# often preferred over writing common software configs from scratch

Attributes & Precedence

# attributes/default.rb
default['nginx']['port'] = 80

# Precedence (lowest to highest):
# default < force_default < normal < override < force_override < automatic
# 'automatic' attributes come from Ohai — collected system facts
# (node['platform'], node['ipaddress']) recipes can reference