Chef Basics

Can I use my existing Chef cookbooks with RightScale?

Yes. If you have already developed your own library of Chef cookbooks and recipes, you can definitely use them in the RightScale system. Although, you might not be able to use them as-is, with a few minor modifications to your existing cookbooks you'll be able to create custom ServerTemplates that use recipes from your own cookbooks. In order to leverage your existing cookbooks you must meet the following requirements.

• The ServerTemplate must use one of the newer RightImages (preferably v5.7 and newer) or use a custom image that includes RightLink v5.7 or newer 
• Each cookbook must have properly formatted Chef Metadata. See Chef Metadata. 

How do I build a Lightweight Resource Provider (LWRP)?

Although you have access to many Chef Resources if you are using an instance that's launched with a v5.7 RightImage and above, as well as to existing LWRPs that are available in RightScale's own cookbook repositories (e.g. 'sys_firewall' and 'block_device'), you may want to create your own LWRP to abstract a repeated pattern of behavior that's currently undefined or inaccessible. To learn how, see Chef Fundamentals LWRP Introduction.

Repository

A software repository is a storage location from which software packages, scripts, etc. can be retrieved. In the Chef community, GitHub is the most commonly used source control management (SCM) system for storing cookbooks. In Chef, a software repository is specifically used to store your Chef cookbooks, resources, and providers and is commonly referred to as a cookbook repository or cookbook repo. And if you are using GitHub, you also might refer to a repository as a GitHub repository or GitHub repo.  

Cookbooks

A Chef cookbook repository consists of one or more cookbooks, where each cookbook applies to a specific topic. For example, you may have a cookbook for databases, applications, setup utilities, etc. Each cookbook contains the Chef components (recipes, resources, attributes, libraries, cookbook files, templates, and metadata) that are needed to configure a server.

Recipes

Recipes are located inside of a Chef cookbook. A recipe is a script written in Chef's domain-specific language (DSL) that will be executed on a running instance. A ServerTemplate consists of scripts that are either RightScripts or Chef recipes. Similar to RightScripts, Chef recipes support variable substitution where inputs (called Chef attributes) allow a user to define values that will be used when the script is executed. A recipe can also contain Chef resources that are located in another cookbook of a referenced repository. 

Attributes

Attributes are displayed as user-configurable inputs in the RightScale dashboard. Attributes are most commonly used in Chef recipes. In order for attributes to be displayed in the dashboard, they must be properly documented in the Chef metadata (metadata.rb). 

Resources

A Chef resource is usually a cross platform abstraction of the thing you're configuring on the host. For example, packages may be installed via apt, yum, or the BSD ports and packages systems, but the package resource abstracts these differences away so that you could use the same recipe to install a package correctly on a variety of systems. Chef's resources are mostly just containers for data with some basic validation functionality. Resources are commonly used in Chef recipes. 

Providers

A provider consists of the platform-specific code that will be executed on a server based on its underlying system architecture. Whereas a Chef resource describes the desired task (e.g. install a package), it's the related Chef provider that actually provides the underlying code that's executed to accomplish the task. Instead of creating a single bash script that contains each supported option through a long list of If/Else statements, you can create a single Chef recipe that leverages existing Chef resources and providers that accomplish the same task in a more efficient and scalable manner.

Ohai

Ohai is a utility that inspects a running instance and discovers relevant system-specific data.

Knife

Knife is a command line interface utility that can be used to create and modify cookbooks. For example you can use knife to create new cookbooks on your Chef development machine. 

Data Bags

Data Bags are used to store nested key–value data (like attributes) that are globally available to all of your Chef-based servers. Data Bag data is searchable and can also be loaded directly by name in a recipe.

RightScale supports the "Data Bag" concept by using inputs. Any Chef attribute can be converted into a user-configurable input. Inputs give you more flexibility than Data Bags because you can define values for these inputs in different places to control the level of inheritance. For example, you can define a value for an input that will be inherited by all servers in a deployment or at the ServerTemplate level if you want to set a default value that can be inherited across your account. See the Intermediate 2 Chef Tutorial for an example of how to create and use inputs.

Search

Search allows you to globally query arbitrary data about your infrastructure. It's most commonly used in a recipe via search calls. 

RightScale supports "Search" functionality using tags and environment variables. The added benefit of using tags instead of Search is that you can use them to discover and manipulate servers. (i.e. You can run a script based on a specific tag.) For example, if you want a set of client servers to connect to the master server at boot time, you could add a tag to the master server and run a script on each client server (at boot time) that establishes a connection to the "master" server based on its tag. Currently, tags are deployment-specific, so you can only use tags to affect servers within the same deployment. Similarly, you could also use a cloud or RightScale-specific environment variable as an input (e.g. PUBLIC_IP, RS_SERVER_NAME, etc.) as a predicatable way to find the "master" server and run a script accordingly using variable substitution. The use of tags can also help you isolate the type of information that you want to be searched. Chef's Search feature lets you search for any piece of information about an entire node of clients, which might be a security concern for your business, whereas RightScale tags let you explicitly define which types of information you want to expose. Use tags to limit what values are externally searchable.

Note: In a future release, RightScale will support the ability to use tags globally in your account across multiple deployments.

Environments

Environments create different work "environments" for each project or phase of a project such as production, staging, development, and testing, etc. Environments are only supported in Chef v0.10.

RightScale supports the concept of environments with deployments. Create deployments using the RightScale Dashboard or API. Use deployments to manage a group of servers that could be deployed across multiple cloud infrastructures. Define deployment-specific inputs to establish consistent server configurations across all servers within a deployment. Execute scripts across multiple servers within the deployment to perform upgrades, failovers, and other lifecycle management tasks.

Roles

Roles define a common set of features across a group of similar nodes (servers). They consist of a name, description, run list of Chef recipes that are executed in order, and a set of node attributes that apply to the recipes. Multiple roles can be used to configure a server. 

RightScale supports the concept of Roles with ServerTemplates. Create a single ServerTemplate that runs a series of recipes to configure a specific type of functional server (e.g. PHP application server) across multiple clouds and operating systems. ServerTemplates also provide a way to include a set of recipes that may or may not be executed over the lifetime of the server to perform various operational tasks so that you can easily change a running server's configuration. For example, instead of having to wait for a reconvergence of your entire system before you can perform a failover to a slave database you can simply run an operational script on-demand. Use a ServerTemplate's operational script list to define actions that are specific to system administrators. ServerTemplates also give you the ability to define acceptable inputs that can be inherited account-wide while also giving you the flexibility override those inputs at the deployment or server level.