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Developer README

This file is intended to provide a place for developers and contributors to document what other developers need to know about changes made to Puppet.

Use of RVM considered dangerous

Use of RVM in production situations, e.g. running CI tests against this repository, is considered dangerous. The reason we consider RVM to be dangerous is because the default behavior of RVM is to hijack the builtin behavior of the shell, causing Gemfile files to be loaded and evaluated when the shell changes directories into the project root.

This behavior causes the CI Job execution environment that runs with set -e to be incompatible with RVM.

We work around this issue by disabling the per-project RC file parsing using

if ! grep -qx rvm_project_rvmrc=0 ~/.rvmrc; then
  echo rvm_project_rvmrc=0 >> ~/.rvmrc

When we setup CI nodes, but this is not standard or expected behavior.

Please consider rbenv instead of rvm. The default behavior of rvm is difficult to maintain with set -e shell environments.

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. I often ran into this when working in Professional Services when I built a small tool to diff two catalogs to determine if an upgrade in Puppet produces the same configuration catalogs. As a developer I've run into this difference while working on spec tests for the static compiler and working on spec tests for 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 terminii 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 ="node-name-val") # NOT certname!
  rsrc ="file", "sshd_config",
    :parameters => {
      :ensure => 'file',
      :source => 'puppet:///modules/filetest/sshd_config',
  rsrc.file = 'site.pp'
  rsrc.line = 21

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 2888.

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 method like so:

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

  class << self
    alias xxx_orig_open open

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

    # 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)

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

Ruby Dependencies

Puppet is considered an Application as it relates to the recommendation of adding a Gemfile.lock file to the repository and the information published at Clarifying the Roles of the .gemspec and Gemfile

To install the dependencies run: bundle install to install the dependencies.

A checkout of the source repository should be used in a way that provides puppet as a gem rather than a simple Ruby library. The parent directory should be set along the GEM_PATH, preferably before other tools such as RVM that manage gemsets using GEM_PATH.

For example, Puppet checked out into /workspace/src/puppet using git checkout in /workspace/src can be used with the following actions. The trick is to symlink gems to src.

$ cd /workspace
$ ln -s src gems
$ mkdir specifications
$ pushd specifications; ln -s ../gems/puppet/puppet.gemspec; popd
$ export GEM_PATH="/workspace:${GEM_PATH}"
$ gem list puppet

This should list out

puppet (2.7.19)


With a source checkout of Puppet properly setup as a gem, dependencies can be installed using Bundler

$ bundle install
Fetching gem metadata from
Using diff-lcs (1.1.3)
Installing facter (1.6.11)
Using metaclass (0.0.1)
Using mocha (0.10.5)
Using puppet (2.7.19) from source at /workspace/puppet-2.7.x/src/puppet
Using rack (1.4.1)
Using rspec-core (2.10.1)
Using rspec-expectations (2.10.0)
Using rspec-mocks (2.10.1)
Using rspec (2.10.0)
Using bundler (1.1.5)
Your bundle is complete! Use `bundle show [gemname]` to see where a bundled gem is installed.

UTF-8 Handling

As Ruby 1.9 becomes more commonly used with Puppet, developers should be aware of major changes to the way Strings and Regexp objects are handled. Specifically, every instance of these two classes will have an encoding attribute determined in a number of ways.

  • If the source file has an encoding specified in the magic comment at the top, the instance will take on that encoding.
  • Otherwise, the encoding will be determined by the LC_LANG or LANG environment variables.
  • Otherwise, the encoding will default to ASCII-8BIT


Excellent information about the differences between encodings in Ruby 1.8 and Ruby 1.9 is published in this blog series: Understanding M17n

Encodings of Regexp and String instances

In general, please be aware that Ruby 1.9 regular expressions need to be compatible with the encoding of a string being used to match them. If they are not compatible you can expect to receive and error such as:

Encoding::CompatibilityError: incompatible encoding regexp match (ASCII-8BIT
regexp with UTF-8 string)

In addition, some escape sequences were valid in Ruby 1.8 are no longer valid in 1.9 if the regular expression is not marked as an ASCII-8BIT object. You may expect errors like this in this situation:

SyntaxError: (irb):7: invalid multibyte escape: /\xFF/

This error is particularly common when serializing a string to other representations like JSON or YAML. To resolve the problem you can explicitly mark the regular expression as ASCII-8BIT using the /n flag:

"a" =~ /\342\230\203/n

Finally, any time you're thinking of a string as an array of bytes rather than an array of characters, common when escaping a string, you should work with everything in ASCII-8BIT. Changing the encoding will not change the data itself and allow the Regexp and the String to deal with bytes rather than characters.

Puppet provides a monkey patch to String which returns an encoding suitable for byte manipulations:

# Example of how to escape non ASCII printable characters for YAML.
>> snowman = "☃"
>> snowman.to_ascii8bit.gsub(/([\x80-\xFF])/n) { |x| "\\x#{x.unpack("C")[0].to_s(16)} }
=> "\\xe2\\x98\\x83"

If the Regexp is not marked as ASCII-8BIT using /n, then you can expect the SyntaxError, invalid multibyte escape as mentioned above.


If you'd like to run Puppet from source on Windows platforms, the include ext/envpuppet.bat will help.

To quickly run Puppet from source, assuming you already have Ruby installed from

gem install sys-admin win32-process win32-dir win32-taskscheduler --no-rdoc --no-ri
gem install win32-service --platform=mswin32 --no-rdoc --no-ri --version 0.7.1
net use Z: "\\vmware-host\Shared Folders" /persistent:yes
cd <path_to_puppet>
set PATH=%PATH%;Z:\<path_to_puppet>\ext
envpuppet puppet --version

Some spec tests are known to fail on Windows, e.g. no mount provider on Windows, so use the following rspec exclude filter:

cd <path_to_puppet>
envpuppet rspec --tag ~fails_on_windows spec

This will give you a shared filesystem with your Mac and allow you to run Puppet directly from source without using install.rb or copying files around.

Common Issues

  • Don't assume file paths start with '/', as that is not a valid path on Windows. Use Puppet::Util.absolute_path? to validate that a path is fully qualified.

  • Use File.expand_path('/tmp') in tests to generate a fully qualified path that is valid on POSIX and Windows. In the latter case, the current working directory will be used to expand the path.

  • Always use binary mode when performing file I/O, unless you explicitly want Ruby to translate between unix and dos line endings. For example, opening an executable file in text mode will almost certainly corrupt the resulting stream, as will occur when using:, 'r') { |f| ... }

    If in doubt, specify binary mode explicitly:, 'rb')

  • Don't assume file paths are separated by ':'. Use File::PATH_SEPARATOR instead, which is ':' on POSIX and ';' on Windows.

  • On Windows, File::SEPARATOR is '/', and File::ALT_SEPARATOR is ''. On POSIX systems, File::ALT_SEPARATOR is nil. In general, use '/' as the separator as most Windows APIs, e.g. CreateFile, accept both types of separators.

  • Don't use waitpid/waitpid2 if you need the child process' exit code, as the child process may exit before it has a chance to open the child's HANDLE and retrieve its exit code. Use Puppet::Util.execute.

  • Don't assume 'C' drive. Use environment variables to look these up:


Configuration Directory

In Puppet 3.x we've simplified the behavior of selecting a configuration file to load. The intended behavior of reading puppet.conf is:

  1. Use the explicit configuration provided by --confdir or --config if present
  2. If running as root (Puppet.features.root?) then use the system puppet.conf
  3. Otherwise, use ~/.puppet/puppet.conf.

When Puppet master is started from Rack, Puppet 3.x will read from ~/.puppet/puppet.conf by default. This is intended behavior. Rack configurations should start Puppet master with an explicit configuration directory using ARGV << "--confdir" << "/etc/puppet". Please see the ext/rack/files/ file for an up-to-date example.

Determining the Puppet Version

If you need to programmatically work with the Puppet version, please use the following:

require 'puppet/version'
# Get the version baked into the sourcecode:
version = Puppet.version
# Set the version (e.g. in a Rakefile based on `git describe`)
Puppet.version = '2.3.4'

Please do not monkey patch the constant Puppet::PUPPETVERSION or obtain the version using the constant. The only supported way to set and get the Puppet version is through the accessor methods.

Static Compiler

The static compiler was added to Puppet in the 2.7.0 release. 1

The static compiler is intended to provide a configuration catalog that requires a minimal amount of network communication in order to apply the catalog to the system. As implemented in Puppet 2.7.x and Puppet 3.0.x this intention takes the form of replacing all of the source parameters of File resources with a content parameter containing an address in the form of a checksum. The expected behavior is that the process applying the catalog to the node will retrieve the file content from the FileBucket instead of the FileServer.

The high level approach can be described as follows. The StaticCompiler is a terminus that inserts itself between the "normal" compiler terminus and the request. The static compiler takes the resource catalog produced by the compiler and filters all File resources. Any file resource that contains a source parameter with a value starting with 'puppet://' is filtered in the following way in a "standard" single master / networked agents deployment scenario:

  1. The content, owner, group, and mode values are retrieved from th FileServer by the master.
  2. The file content is stored in the file bucket on the master.
  3. The source parameter value is stripped from the File resource.
  4. The content parameter value is set in the File resource using the form '{XXX}1234567890' which can be thought of as a content address indexed by checksum.
  5. The owner, group and mode values are set in the File resource if they are not already set.
  6. The filtered catalog is returned in the response.

In addition to the catalog terminus, the process requesting the catalog needs to obtain the file content. The default behavior of puppet agent is to obtain file contents from the local client bucket. The method we expect users to employ to reconfigure the agent to use the server bucket is to declare the Filebucket[puppet] resource with the address of the master. For example:

node default {
  filebucket { puppet:
    server => $server,
    path   => false,
  class { filetest: }

This special filebucket resource named "puppet" will cause the agent to fetch file contents specified by checksum from the remote filebucket instead of the default clientbucket.

Quick start

Create a module that recursively downloads something. The jeffmccune-filetest module will recursively copy the rubygems source tree.

$ puppet module install jeffmccune-filetest

Start the master with the StaticCompiler turned on:

$ puppet master \
    --catalog_terminus=static_compiler \
    --verbose \

Add the special Filebucket[puppet] resource:

# site.pp
node default {
  filebucket { puppet: server => $server, path => false }
  class { filetest: }

Get the static catalog:

$ puppet agent --test

You should expect all file metadata to be contained in the catalog, including a checksum representing the content. When managing an out of sync file resource, the real contents should be fetched from the server instead of the clientbucket.