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Two Types of Catalog

When working on subsystems of Puppet that deal with the catalog it is important to be aware of the two different types of Catalog. Developers will often find this difference while working on the static compiler and types and providers.

The two different types of catalog becomes relevant when writing spec tests because we frequently need to wire up a fake catalog so that we can exercise types, providers, or termini that filter the catalog.

The two different types of catalogs are so-called "resource" catalogs and "RAL" (resource abstraction layer) catalogs. At a high level, the resource catalog is the in-memory object we serialize and transfer around the network. The compiler terminus is expected to produce a resource catalog. The agent takes a resource catalog and converts it into a RAL catalog. The RAL catalog is what is used to apply the configuration model to the system.

Resource dependency information is most easily obtained from a RAL catalog by walking the graph instance produced by the relationship_graph method.

Resource Catalog

If you're writing spec tests for something that deals with a catalog "server side," a new catalog terminus for example, then you'll be dealing with a resource catalog. You can produce a resource catalog suitable for spec tests using something like this:

let(:catalog) do
  catalog = Puppet::Resource::Catalog.new("node-name-val") # NOT certname!
  rsrc = Puppet::Resource.new("file", "sshd_config",
    :parameters => {
      :ensure => 'file',
      :source => 'puppet:///modules/filetest/sshd_config',
    }
  )
  rsrc.file = 'site.pp'
  rsrc.line = 21
  catalog.add_resource(rsrc)
end

The resources in this catalog may be accessed using catalog.resources. Resource dependencies are not easily walked using a resource catalog however. To walk the dependency tree convert the catalog to a RAL catalog as described in

RAL Catalog

The resource catalog may be converted to a RAL catalog using catalog.to_ral. The RAL catalog contains Puppet::Type instances instead of Puppet::Resource instances as is the case with the resource catalog.

One very useful feature of the RAL catalog are the methods to work with resource relationships. For example:

irb> catalog = catalog.to_ral
irb> graph = catalog.relationship_graph
irb> pp graph.edges
[{ Notify[alpha] => File[/tmp/file_20.txt] },
 { Notify[alpha] => File[/tmp/file_21.txt] },
 { Notify[alpha] => File[/tmp/file_22.txt] },
 { Notify[alpha] => File[/tmp/file_23.txt] },
 { Notify[alpha] => File[/tmp/file_24.txt] },
 { Notify[alpha] => File[/tmp/file_25.txt] },
 { Notify[alpha] => File[/tmp/file_26.txt] },
 { Notify[alpha] => File[/tmp/file_27.txt] },
 { Notify[alpha] => File[/tmp/file_28.txt] },
 { Notify[alpha] => File[/tmp/file_29.txt] },
 { File[/tmp/file_20.txt] => Notify[omega] },
 { File[/tmp/file_21.txt] => Notify[omega] },
 { File[/tmp/file_22.txt] => Notify[omega] },
 { File[/tmp/file_23.txt] => Notify[omega] },
 { File[/tmp/file_24.txt] => Notify[omega] },
 { File[/tmp/file_25.txt] => Notify[omega] },
 { File[/tmp/file_26.txt] => Notify[omega] },
 { File[/tmp/file_27.txt] => Notify[omega] },
 { File[/tmp/file_28.txt] => Notify[omega] },
 { File[/tmp/file_29.txt] => Notify[omega] }]

If the relationship_graph method is throwing exceptions at you, there's a good chance the catalog is not a RAL catalog.

Settings Catalog

Be aware that Puppet creates a mini catalog and applies this catalog locally to manage file resource from the settings. This behavior made it difficult and time consuming to track down a race condition in PUP-1070.

Even more surprising, the File[puppetdlockfile] resource is only added to the settings catalog if the file exists on disk. This caused the race condition as it will exist when a separate process holds the lock while applying the catalog.

It may be sufficient to simply be aware of the settings catalog and the potential for race conditions it presents. An effective way to be reasonably sure and track down the problem is to wrap the File.open method like so:

# We're wrapping ourselves around the File.open method.
# As described at: https://goo.gl/lDsv6
class File
  WHITELIST = [ /pidlock.rb:39/ ]

  class << self
    alias xxx_orig_open open
  end

  def self.open(name, *rest, &block)
    # Check the whitelist for any "good" File.open calls against the #
    puppetdlock file
    white_listed = caller(0).find do |line|
      JJM_WHITELIST.find { |re| re.match(line) }
    end

    # If you drop into IRB here, take a look at your caller, it might be
    # the ghost in the machine you're looking for.
    binding.pry if name =~ /puppetdlock/ and not white_listed
    xxx_orig_open(name, *rest, &block)
  end
end

The settings catalog is populated by the Puppet::Util::Settings#to\_catalog method.