Way to pass parameters at run time in Chef

chef

I wanted to pass some attributes to chef-client at runtime. Is there a way to do the same?
I was looking into chef-client -j option, but to my knowledge it can be used to specify run_list. Can I pass some attributes in it? If yes, how?

Best Answer

Yes, you can use the -j json file option to populate node attributes.

{
  "my_attribute": "I like attributes!"
}

This will make an attribute named my_attribute available in your cookbooks. For example,

Chef::Log.info(node['my_attribute'])

Or,

if node['my_attribute'] =~ /like/
  package "foo-likes-attributes" do
    action :install
  end
end

Setting an initial run_list is the most common use of the json attributes file for Chef Client. If you're using Chef Client + Chef Server, though, you can simply modify the node object on the server either through the webui (Open Source Chef Server) or management console (Opscode Hosted/Private Chef), or through knife node edit if you're using the command-line tool, knife.

Note that using the JSON file is like modifying the node object on the server, the attributes set here "normal" priority like when they are used in a recipe, and these attribute values will be saved to the Node object on the server at the end of a successful run.

Normal attributes applied on a node directly in a recipe (from the documentation)

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Idiomatic way to invoke chef-solo

By default, chef-solo reads its configuration from /etc/chef/solo.rb. The command-line parameters correspond to config values that can be set in this file. This is done using the mixlib-config library.

  option :config_file, 
    :short => "-c CONFIG",
    :long  => "--config CONFIG",
    :default => "/etc/chef/solo.rb",
    :description => "The configuration file to use"

  option :json_attribs,
    :short => "-j JSON_ATTRIBS",
    :long => "--json-attributes JSON_ATTRIBS",
    :description => "Load attributes from a JSON file or URL",
    :proc => nil

  option :recipe_url,
      :short => "-r RECIPE_URL",
      :long => "--recipe-url RECIPE_URL",
      :description => "Pull down a remote gzipped tarball of recipes and untar it to the cookbook ca
che.",
      :proc => nil

The 'option' is the config file value.

The actual config file, /etc/chef/solo.rb would look like:

file_cache_path "/tmp/chef-solo"
cookbook_path   "/tmp/chef-solo/cookbooks"
role_path       "/tmp/chef-solo/roles"
json_attribs    "/tmp/chef-solo/node.json"
recipe_url      "http://www.example.com/chef-solo.tar.gz"

Also note that the JSON file can be a remote URL, too.

json_attribs    "http://www.example.com/node.json"

You can use Ohai as a library within the config file as well, to detect the platform or other attributes to specify what JSON file to use.

require 'rubygems'
require 'ohai'
o = Ohai::System.new
o.all_plugins
file_cache_path "/tmp/chef-solo"
cookbook_path   "/tmp/chef-solo/cookbooks"
role_path       "/tmp/chef-solo/roles"
json_attribs    "/tmp/chef-solo/#{o[:platform]}.json"
recipe_url      "http://www.example.com/chef-solo.tar.gz"

And then you'd have "platform" specific JSON files, for example. Or you could use o[:hostname], o[:domain] or o[:fqdn] to use JSON files based on the hostname, domain or fqdn. But once you start having the scaffolding of servers to support this kind of dynamic configuration, you might look at running a Chef Server :-).

Chef = Node Attribute, how to Manage them locally, versioned and then upload them

In Chef, the node is the authority. The best practice is to use knife bootstrap to get a system set up to run chef and integrate it with the Chef server.

The majority of the node attribute data is generated dynamically by the node when chef-client runs, where it uses ohai to discover information about itself. Other data can come from cookbooks and roles. Your cookbooks and roles should certainly be stored in your version control repository, in what is typically called the Chef Repository.

The main reason to store nodes locally is to capture their run lists. We recommend that you have a runbook document in your repository (like a README :)) that describes what kinds of servers you have and what their roles are.

Best Answer

Related Solutions

Idiomatic way to invoke chef-solo

Chef = Node Attribute, how to Manage them locally, versioned and then upload them

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