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AWS OpsWorks
User Guide (API Version 2013-02-18)

Recipe Structure

A cookbook is primarily a set of recipes, which can perform a wide variety of tasks on an instance. To clarify how to implement recipes, it's useful to look at a simple example. The following is the setup recipe for the built-in HAProxy layer. Just focus on the overall structure at this point and don't worry too much about the details; they will be covered in the subsequent examples.

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package 'haproxy' do action :install end if platform?('debian','ubuntu') template '/etc/default/haproxy' do source 'haproxy-default.erb' owner 'root' group 'root' mode 0644 end end include_recipe 'haproxy::service' service 'haproxy' do action [:enable, :start] end template '/etc/haproxy/haproxy.cfg' do source 'haproxy.cfg.erb' owner 'root' group 'root' mode 0644 notifies :restart, "service[haproxy]" end

Note

For this and other examples of working recipes and related files, see the AWS OpsWorks Stacks built-in recipes.

The example highlights the key recipe elements, which are described in the following sections.

Resources

Recipes consist largely of a set of Chef resources. Each one specifies a particular aspect of the instance's final state, such as a package to be installed or a service to be started. The example has four resources:

  • A package resource, which represents an installed package, an HAProxy server for this example.

  • A service resource, which represents a service, the HAProxy service for this example.

  • Two template resources, which represent files that are to be created from a specified template, two HAProxy configuration files for this example.

Resources provide a declarative way to specify the instance state. Behind the scenes, each resource has an associated provider that performs the required tasks, such as installing packages, creating and configuring directories, starting services, and so on. If the details of the task depend on the particular operating system, the resource has multiple providers and uses the appropriate one for the system. For example, on a Red Hat Linux system the package provider uses yum to install packages. On a Ubuntu Linux system, the package provider uses apt-get.

You implement a resource as a Ruby code block with the following general format.

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resource_type "resource_name" do attribute1 'value1' attribute2 'value2' ... action :action_name notifies : action 'resource' end

The elements are:

Resource type

(Required) The example includes three resource types, package, service, and template.

Resource name

(Required) The name identifies the particular resource and is sometimes used as a default value for one of the attributes. In the example, package represents a package resource named haproxy and the first template resource represents a configuration file named /etc/default/haproxy.

Attributes

(Optional) Attributes specify the resource configuration and vary depending on the resource type and how you want to configure the resource.

  • The example's template resources explicitly define a set of attributes that specify the created file's source, owner, group, and mode.

  • The example's package and service resources do not explicitly define any attributes.

    The resource name is typically the default value for a required attribute and is sometimes all that is needed. For example, the resource name is the default value for the package resource's package_name attribute, which is the only required attribute.

There are also some specialized attributes called guard attributes, which specify when the resource provider is to take action. For example, the only_if attribute directs the resource provider to take action only if a specified condition is met. The HAProxy recipe does not use guard attributes, but they are used by several of the following examples.

Actions and Notifications

(Optional) Actions and notifications specify what tasks the provider is to perform.

  • action directs the provider to take a specified action, such as install or create.

    Each resource has a set of actions that depend on the particular resource, one of which is the default action. In the example, the package resource's action is install, which directs the provider to install the package. The first template resource has no action element, so the provider takes the default create action.

  • notifies directs another resource's provider to perform an action, but only if the resource's state has changed.

    notifies is typically used with resources such as template and file to perform tasks such as restarting a service after modifying a configuration file. Resources do not have default notifications. If you want a notification, the resource must have an explicit notifies element. In the HAProxy recipe, the second template resource notifies the haproxy service resource to restart the HAProxy service if the associated configuration file has changed.

Resources sometimes depend on operating system.

  • Some resources can be used only on Linux or Windows systems.

    For example, package installs packages on Linux systems and windows_package installs packages on Windows systems.

  • Some resources can be used with any operating system, but have attributes that are specific to a particular system.

    For example, the file resource can be used on either Linux or Windows systems, but has separate sets of attributes for configuring permissions.

For descriptions of the standard resources, including the available attributes, actions, and notifications for each resource, see About Resources and Providers.

Flow Control

Because recipes are Ruby applications, you can use Ruby control structures to incorporate flow control into a recipe. For example, you can use Ruby conditional logic to have the recipe behave differently on different systems. The HAProxy recipe includes an if block that uses a template resource to create a configuration file, but only if the recipe is running on a Debian or Ubuntu system.

Another common scenario is using a loop to execute a resource multiple times with different attribute settings. For example, you can create a set of directories by using a loop to execute a directory resource multiple times with different directory names.

Note

If you aren't familiar with Ruby, see Just Enough Ruby for Chef, which covers what you need to know for most recipes.

Included Recipes

include_recipe includes other recipes in your code, which allows you to modularize your recipes and reuse the same code in multiple recipes. When you run the host recipe, Chef replaces each include_recipe element with the specified recipe's code before it executes the host recipe. You identify an included recipe by using the standard Chef cookbook_name::recipe_name syntax, where recipe_name omits the .rb extension. The example includes one recipe, haproxy::service, which represents the HAProxy service.

Note

If you use include_recipe in recipes running on Chef 11.10 and later to include a recipe from another cookbook, you must use a depends statement to declare the dependency in the cookbook's metadata.rb file. For more information, see Implementing Recipes: Chef 11.10.