chef - When automatic attributes(Ohai data) get update? -

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from introduction of http://docs.opscode.com/chef_overview_attributes.html#automatic-ohai, says "an automatic attribute contains data identified ohai at beginning of every chef-client run. automatic attribute cannot modified , has highest attribute precedence."

from understanding:

  1. automatic attributes cannot modified.
  2. automatic attributes updated when chef-client runs

for number 1, it's not true. i'm able modify automatic attribute. instance, change version of chef package:

require 'chef' chef::config.from_file(file.join('/home/chefuser', '.chef', 'knife.rb')) query = chef::search::query.new  # search node node name, test_machine in case nodes = query.search('node', "name:test_machine").first  nodes[0].automatic["chef_packages"]["chef"]["version"] = "11.12.2" nodes[0].save

and using

knife node show test_machine -l | grep version

the version of chef package has been changed. question: right way modify automatic attributes? or not necessary change automatic attributes, because ohai automatically?

for number 2, question: mean "at beginning of chef-client run"? automatic attributes never updated if chef-client not run?

i suppose automatic attributes should updated once system configuration being changed. i'm wondering when automatic attributes updated without running chef-client.

automatic attributes can't modified in context of chef client run. if set attribute on saved node object (which code doing), reset @ start of every chef client run , value ohai override it.

here's rough sequence of events during chef client run:

  1. chef retrieves saved node object chef server (if 1 exists)
  2. it applies attribute overrides cookbooks/roles/recipes
  3. it applies automatic attributes provided ohai
  4. it executes run list using updated state
  5. it saves updated node object on chef server if run succeeded

so if need correct automatic attributes within chef-client run, don't have since happens automatically.

edit: can find more details attribute persistence , precedence here.


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