An Overview of Chef Infra
Chef Infra is a powerful automation platform that transforms infrastructure into code. Whether you’re operating in the cloud, on-premises, or in a hybrid environment, Chef Infra automates how infrastructure is configured, deployed, and managed across your network, no matter its size.
This diagram shows how you develop, test, and deploy your Chef Infra code.
- Chef Workstation is the location where users interact with Chef Infra. With Chef Workstation, users can author and test cookbooks using tools such as Test Kitchen and interact with the Chef Infra Server using the knife and chef command line tools.
- Chef Infra Client nodes are the machines that are managed by Chef Infra. The Chef Infra Client is installed on each node and is used to configure the node to its desired state.
- Chef Infra Server acts as a hub for configuration data. Chef Infra Server stores cookbooks, the policies that are applied to nodes, and metadata that describes each registered node that is being managed by Chef. Nodes use the Chef Infra Client to ask the Chef Infra Server for configuration details, such as recipes, templates, and file distributions.
Chef Infra Components
The following diagram shows the relationships between the various elements of Chef Infra, including the nodes, the server, and the workstation. These elements work together to provide the Chef Infra Client the information and instruction that it needs so that it can do its job. As you are reviewing the rest of this topic, use the icons in the tables to refer back to this image.
Chef Infra has the following major components:
One (or more) workstations are configured to allow users to author, test, and maintain cookbooks.
Workstation systems run the Chef Workstation package which includes tools such as Chef Infra Client, Chef InSpec, Test Kitchen, ChefSpec, Cookstyle, and other tools necessary for developing and testing your infrastructure with Chef products.
Cookbooks are uploaded to the Chef Infra Server from these workstations. Some cookbooks are custom to the organization and others are based on community cookbooks available from the Chef Supermarket.
Ruby is the programming language that is the authoring syntax for cookbooks. Most recipes are simple patterns (blocks that define properties and values that map to specific configuration items like packages, files, services, templates, and users. The full power of Ruby is available for when you need a programming language.
A node is any device---physical, virtual, cloud, network device, etc.---that is under management by Chef Infra.
Chef Infra Client is installed on each node that is managed with Chef Infra. Chef Infra Client configures the node locally by performing the tasks specified in the run-list. Chef Infra Client will also pull down any required configuration data from the Chef Infra Server during a Chef Infra Client run.
The Chef Infra Server acts as a hub of information. Cookbooks and policy settings are uploaded to the Chef Infra Server by users from workstations. (Policy settings may also be maintained from the Chef Infra Server itself, via the Chef management console web user interface.)
The Chef Infra Client accesses the Chef Infra Server from the node on which it's installed to get configuration data, performs searches of historical Chef Infra Client run data, and then pulls down the necessary configuration data. After a Chef Infra Client run is finished, the Chef Infra Client uploads updated run data to the Chef Infra Server.
|Chef Supermarket is the location in which community cookbooks are shared and managed. Cookbooks that are part of the Chef Supermarket may be used by any Chef user. How community cookbooks are used varies from organization to organization.|
Chef Infra Client run reporting, compliance reporting, high availability configurations, and Chef Infra Server replication are available as part of Chef Automate.
The following sections discuss these elements (and their various components) in more detail.
A workstation is your local computer running Chef Workstation that you use to author cookbooks, interact with the Chef Infra Server, and interact with nodes.
The workstation is where users do most of their work, including:
- Developing and testing cookbooks and recipes
- Testing Chef code
- Keeping the Chef repository synchronized with version source control
- Configuring organizational policy, including defining roles and environments, and ensuring that critical data is stored in data bags
- Interacting with nodes, as (or when) required, such as performing a bootstrap operation
Chef Workstation Components and Tools
Some important tools and components of Chef Workstation include:
|Chef Workstation contains everything that is needed to start using Chef
Infra and Chef InSpec:
Chef Workstation includes important command-line tools:
The chef-repo is the repository structure in which cookbooks are authored, tested, and maintained:
The directory structure within the chef-repo varies. Some organizations prefer to keep all of their cookbooks in a single chef-repo, while other organizations prefer to use a chef-repo for every cookbook.
|Use [Test Kitchen](https://kitchen.ci/) to automatically test cookbooks across any combination of platforms and test suites:|
|Use ChefSpec to simulate the convergence of resources on a node:
A cookbook is the fundamental unit of configuration and policy distribution. A cookbook defines a scenario and contains everything that is required to support that scenario:
- Recipes that specify the resources to use and the order in which they are to be applied
- Attribute values
- File distributions
- Extensions to Chef, such as custom resources and libraries
The Chef Infra Client uses Ruby as its reference language for creating cookbooks and defining recipes, with an extended DSL for specific resources. A reasonable set of resources are available to the Chef Infra Client, enough to support many of the most common infrastructure automation scenarios; however, this DSL can also be extended when additional resources and capabilities are required.
Cookbooks are comprised of the following components:
|An attribute can be defined in a cookbook (or a recipe) and then used to override the default settings on a node. When a cookbook is loaded during a Chef Infra Client run, these attributes are compared to the attributes that are already present on the node. Attributes that are defined in attribute files are first loaded according to cookbook order. For each cookbook, attributes in the `default.rb` file are loaded first, and then additional attribute files (if present) are loaded in lexical sort order. When the cookbook attributes take precedence over the default attributes, Chef Infra Client applies those new settings and values during a Chef Infra Client run on the node.|
|Use the **cookbook_file** resource to transfer files from a sub-directory of `COOKBOOK_NAME/files/` to a specified path located on a host that is running Chef Infra Client. The file is selected according to file specificity, which allows different source files to be used based on the hostname, host platform (operating system, distro, or as appropriate), or platform version. Files that are located in the `COOKBOOK_NAME/files/default` sub-directory may be used on any platform.|
|A library allows arbitrary Ruby code to be included in a cookbook. The most common use for libraries is to write helpers that are used throughout recipes and custom resources. A library file is a Ruby file that is located within a cookbook's `/libraries` directory. Because a library is built using Ruby, anything that can be done with Ruby can be done in a library file, including advanced functionality such as extending built-in Chef classes.|
|Every cookbook requires a small amount of metadata. A file named metadata.rb is located at the top of every cookbook directory structure. The contents of the metadata.rb file provides information that helps Chef Infra Client and Server correctly deploy cookbooks to each node.|
A recipe is the most fundamental configuration element within the organization. A recipe:
The Chef Infra Client will run a recipe only when asked. When the Chef Infra Client runs the same recipe more than once, the results will be the same system state each time. When a recipe is run against a system, but nothing has changed on either the system or in the recipe, the Chef Infra Client won't change anything.
The Recipe DSL is a Ruby DSL that is primarily used to declare resources from within a recipe. The Recipe DSL also helps ensure that recipes interact with nodes (and node properties) in the desired manner. Most of the methods in the Recipe DSL are used to find a specific parameter and then tell Chef Infra Client what action(s) to take, based on whether that parameter is present on a node.
A resource is a statement of configuration policy that:
Chef has many built-in resources that cover all of the most common actions across all of the most common platforms. You can build your own resources to handle any situation that isn't covered by a built-in resource.
|A cookbook template is an Embedded Ruby (ERB) template that is used to dynamically generate static text files. Templates may contain Ruby expressions and statements, and are a great way to manage configuration files. Use the **template** resource to add cookbook templates to recipes; place the corresponding Embedded Ruby (ERB) template file in a cookbook's `/templates` directory.|
|Testing cookbooks improves the quality of those cookbooks by ensuring they are doing what they are supposed to do and that they are authored in a consistent manner. Unit and integration testing validates the recipes in cookbooks. Syntax testing---often called linting---validates the quality of the code itself. The following tools are popular tools used for testing Chef recipes: Test Kitchen, ChefSpec, and Cookstyle.|
A node is any device—physical, virtual, cloud, network device, etc.—that is under management by Chef Infra.
The types of nodes that can be managed by Chef include, but are not limited to, the following:
|A physical node is typically a server or a virtual machine, but it can be any active device attached to a network that is capable of sending, receiving, and forwarding information over a communications channel. In other words, a physical node is any active device attached to a network that can run a Chef Infra Client and also allow that Chef Infra Client to communicate with a Chef Infra Server.|
|A cloud-based node is hosted in an external cloud-based service, such as Amazon Web Services (AWS), OpenStack, Rackspace, Google Compute Engine, or Microsoft Azure. Plugins are available for knife that provide support for external cloud-based services. knife can use these plugins to create instances on cloud-based services. Once created, Chef Infra Client can be used to deploy, configure, and maintain those instances.|
|A virtual node is a machine that runs only as a software implementation, but otherwise behaves much like a physical machine.|
|A network node is any networking device---a switch, a router---that is being managed by a Chef Infra Client, such as networking devices by Juniper Networks, Arista, Cisco, and F5. Use Chef to automate common network configurations, such as physical and logical Ethernet link properties and VLANs, on these devices.|
|Containers are an approach to virtualization that allows a single operating system to host many working configurations, where each working configuration---a container---is assigned a single responsibility that is isolated from all other responsibilities. Containers are popular as a way to manage distributed and scalable applications and services.|
Chef on Nodes
The key components of nodes that are under management by Chef include:
Chef Infra Client is an agent that runs locally on every node that is under management by Chef Infra Server. When Chef Infra Client runs, performs all of the steps required for bringing a node into the expected state, including:
Chef Infra Client authenticates with the Chef Infra Server using RSA public key-pairs each time a Chef Infra Client needs access to data that is stored on the Chef Infra Server. This prevents any node from accessing data that it shouldn't and it ensures that only nodes that are properly registered with the Chef Infra Server can be managed.
|Ohai is a tool that is used to collect system configuration data, which
is provided to Chef Infra Client for use within cookbooks. Ohai is run
by Chef Infra Client at the beginning of every Chef run to determine
system state. Ohai includes many built-in plugins to detect common
configuration details as well as a plugin model for writing custom
The types of attributes Ohai collects include but are not limited to:
Attributes that are collected by Ohai are automatic level attributes, in that these attributes are used by Chef Infra Client to ensure that these attributes remain unchanged after Chef Infra Client is done configuring the node.
The Chef Infra Server
The Chef Infra Server acts as a hub for configuration data. The Chef Infra Server stores cookbooks, the policies that are applied to nodes, and metadata that describes each registered node that is being managed by Chef Infra Client. Nodes use Chef Infra Client to ask the Chef Infra Server for configuration details, such as recipes, templates, and file distributions. Chef Infra Client then does as much of the configuration work as possible on the nodes themselves (and not on the Chef Infra Server). This scalable approach distributes the configuration effort throughout the organization.
|Search indexes allow queries to be made for any type of data that is indexed by the Chef Infra Server, including data bags (and data bag items), environments, nodes, and roles. A defined query syntax is used to support search patterns like exact, wildcard, range, and fuzzy. A search is a full-text query that can be done from several locations, including from within a recipe, by using the `search` subcommand in knife, the `search` method in the Recipe DSL, the search box in the Chef management console, and by using the `/search` or `/search/INDEX` endpoints in the Chef Infra Server API. The search engine is based on Apache Solr and is run from the Chef Infra Server.|
|Chef management console is a web-based interface for the Chef Infra
Server that provides users a way to manage the following objects:
|Data bags store global variables as JSON data. Data bags are indexed for searching and can be loaded by a cookbook or accessed during a search.|
|Policy defines how business and operational requirements, processes, and production workflows map to objects that are stored on the Chef Infra Server. Policy objects on the Chef Infra Server include roles, environments, and cookbook versions.|
Policy maps business and operational requirements, process, and workflow to settings and objects stored on the Chef Infra Server:
- Roles define server types, such as “web server” or “database server”
- Environments define process, such as “dev”, “staging”, or “production”
- Certain types of data—passwords, user account data, and other sensitive items—can be placed in data bags, which are located in a secure sub-area on the Chef Infra Server that can only be accessed by nodes that authenticate to the Chef Infra Server with the correct SSL certificates
- The cookbooks (and cookbook versions) in which organization-specific configuration policies are maintained
Some important aspects of policy include:
|A role is a way to define certain patterns and processes that exist across nodes in an organization as belonging to a single job function. Each role consists of zero (or more) attributes and a run-list. Each node can have zero (or more) roles assigned to it. When a role is run against a node, the configuration details of that node are compared against the attributes of the role, and then the contents of that role's run-list are applied to the node's configuration details. When a Chef Infra Client runs, it merges its own attributes and run-lists with those contained within each assigned role.|
|An environment is a way to map an organization's real-life workflow to what can be configured and managed when using Chef Infra. This mapping is accomplished by setting attributes and pinning cookbooks at the environment level. With environments, you can change cookbook configurations depending on the system's designation. For example, by designating different staging and production environments, you can then define the correct URL of a database server for each environment. Environments also allow organizations to move new cookbook releases from staging to production with confidence by stepping releases through testing environments before entering production.|
|A cookbook version represents a set of functionality that is different
from the cookbook on which it is based. A version may exist for many
reasons, such as ensuring the correct use of a third-party component,
updating a bug fix, or adding an improvement. A cookbook version is
defined using syntax and operators, may be associated with environments,
cookbook metadata, and/or run-lists, and may be frozen (to prevent
unwanted updates from being made).
A cookbook version is maintained just like a cookbook, with regard to source control, uploading it to the Chef Infra Server, and how Chef Infra Client applies that cookbook when configuring nodes.
|A run-list defines all of the information necessary for Chef to
configure a node into the desired state. A run-list is:
Chef is a thin DSL (domain-specific language) built on top of Ruby. This approach allows Chef to provide just enough abstraction to make reasoning about your infrastructure easy. Chef includes a built-in taxonomy of all the basic resources one might configure on a system, plus a defined mechanism to extend that taxonomy using the full power of the Ruby language. Ruby was chosen because it provides the flexibility to use both the simple built-in taxonomy, as well as being able to handle any customization path your organization requires.