Recipes

Recipes are the core component of getting things done. They are scripts, written in Ruby, that provide the instructions to be executed on end hosts when the Chef client is run. Recipes are placed in the recipes directory inside of a cookbook, and each recipe is designed to achieve a specific purpose, such as provisioning accounts, installing and configuring a database server, and custom software deployments.

Recipes combine configuration data with the current state of the host to execute commands that will cause the system to enter a new state. For example, a PostgreSQL database server recipe would have the goal of installing and starting a PostgreSQL server on any host that runs the recipe. Let's look at a few possible starting states and the expected behavior:

To achieve these goals, recipes use a combination of resources, configuration data, and Ruby code to determine what to execute on the end host. Each host-level resource—files, configuration files, packages, users, and so on—is mapped to a Chef resource in a recipe. For example, consider the recipe that we saw earlier in the book that was used to demonstrate that the Chef-solo installation was functional:

file "#{ENV['HOME']}/example.txt" do
  action :create
  content "Greetings #{ENV['USER']}!"
end

This is a complete recipe; it has one step to create a file, and that is all it does. The file being created on the end host needs a name; here, it will be named ENV['HOME']/example.txt, which is Ruby's way of representing $HOME/example.txt. In addition to a name, we are instructing Chef to create the file (we could just as easily instruct Chef to delete the file) and to put the contents Greetings $USER into the file, replacing what is in there.

We could extend our recipe to ensure that a specific user existed on the host and create a file with the owner set to the newly created user:

user "smith" do
  action :create
  system true
  comment "Agent Smith"
  uid  1000
  gid  "agents"
  home "/home/matrix"
  shell "/bin/zsh"
end 

file "/tmp/agent.txt" do
  action :create
  content "Hello from smith!"
  owner "smith"
  group "agents"
  mode "0660"
end

Each recipe is a script that is run from beginning to end, assuming that nothing causes it to abort. Also, each recipe can access the node's attribute data and leverage resources to compile templates, create directories, install packages, execute commands, download files, and do just about anything that you can do from a shell as an administrator. If you can't accomplish what you need to do using the existing Chef resources, you can either create your own custom resources, or you can execute an arbitrary user-defined shell script.