Chef Configuration Concepts

Policy determines what state a node should be in, resource executes steps to bring the node into that state by mapping to a provider (such as yum or apt-get)

Policy

  • A collection of system configurations that you define (roles/databags/environments)
  • The policy states the state that each resource should be in but not how to get there
  • chef-client will pull the policy and configure the node so that it matches the state of the policy

Policy concept examples:
- If it should be installed
- If it is not installed then install it
- If it is already installed then do nothing
- A file should exist - if not, create it
- If a file exists but does not have correct content, correct it

Resources

Resources define the desired state for a single configuration item present on a node that is under management by Chef

  • Performs the configuration on a node and maps to providers
  • Recipes are stored in cookbooks
  • Building blocks of Chef configuration
  • When chef-client is run on a node, the resource is executed by the provider which is handled by Chef and the OS itself
  • Information as to what provider to use (ie what package manager to use) is populated when Ohai is run at the start of each chef-client run

Most common resources:
- Package: Used to manage packages such as installing packages
- Template: Used to manage the contents of a Ruby template in the cookbook
- Service: Manage system services - what run levels to start the service in, current state of the service (running/stopped/etc)