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+++ title = "About Nodes" draft = false gh_repo = "chef-web-docs"

product = ["client", "server"]

[menu] [menu.infra] title = "Nodes" identifier = "chef_infra/overview/nodes.md Nodes" parent = "chef_infra/overview" weight = 30 +++

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The key components of nodes that are under management by Chef include:

Component Description

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Node Names

The name of a node is required as part of the authentication process to the Chef Infra Server. The name of each node must be unique within an organization, but otherwise can be any string that matches the following regular expression:

 /^[\-[:alnum:]_:.]+$/

The name of a node can be obtained from the node_name attribute in the client.rb file or by allowing Ohai to collect this data during a Chef Infra Client run. When Ohai collects this data during a Chef Infra Client run, it uses the node's FQDN, which is always unique within an organization, as the name of the node.

Using the FQDN as the node name, and then allowing Ohai to collect this information during each Chef Infra Client run, is the recommended approach and the easiest way to ensure that the names of all nodes across the organization are unique.

Node Objects

For Chef Infra Client, two important aspects of nodes are groups of attributes and run-lists. An attribute is a specific piece of data about the node, such as a network interface, a file system, or the number of clients a service running on a node is capable of accepting. A run-list is an ordered list of recipes and/or roles that are run in an exact order. The node object consists of the run-list and node attributes, which is a JSON file that's stored on the Chef Infra Server. Chef Infra Client gets a copy of the node object from the Chef Infra Server during each Chef Infra Client run and places an updated copy on the Chef Infra Server at the end of each Chef Infra Client run.

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Attributes

An attribute is a specific detail about a node, such as an IP address, a host name, a list of loaded kernel modules, the versions of available programming languages that are available. An attribute may be unique to a specific node or it can be identical across every node in the organization. Attributes are most commonly set from a cookbook, by using knife, or are retrieved by Ohai from each node before every Chef Infra Client run. All attributes are indexed for search on the Chef Infra Server. Good candidates for attributes include:

  • any cross-platform abstraction for an application, such as the path to a configuration file
  • default values for tunable settings, such as the amount of memory assigned to a process or the number of workers to spawn
  • anything that may need to be persisted in node data between Chef Infra Client runs

In general, attribute precedence is set to enable cookbooks and roles to define attribute defaults, for normal attributes to define the values that should be specific for a node, and for override attributes to force a certain value, even when a node already has that value specified.

One approach is to set attributes at the same precedence level by setting attributes in a cookbook's attribute files, and then also setting the same default attributes (but with different values) using a role. The attributes set in the role will be deep merged on top of the attributes from the attribute file, and the attributes set by the role will take precedence over the attributes specified in the cookbook's attribute files.

See Attributes for detailed information on the different types of node attributes and how they're used to set policy on nodes.

Run-lists

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Run-list Format

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Managing Nodes

You can manage nodes directly using Knife, Chef Automate, or by using command-line tools that are specific to Chef Infra Client.

  • Knife can be used to create, edit, view, list, tag, and delete nodes.
  • Knife plug-ins can be used to create, edit, and manage nodes that are located on cloud providers.
  • Chef Infra Client can be used to manage node data using the command line and JSON files. Each JSON file contains a hash, the elements of which are added as node attributes. In addition, the run_list setting allows roles and/or recipes to be added to the node.
  • The command line can also be used to edit JSON files and files that are related to third-party services, such as Amazon EC2, where the JSON files can contain metadata fore each instance that's stored in a file on-disk and then read by Chef Infra Client as required.