This document discusses Puppet modules and Example42's approach. It outlines how Example42 develops Puppet modules following best practices for reusability, standardization, and interoperability. Their next generation modules provide features like automatic monitoring, firewalling, and Puppi integration while allowing high levels of customization through parameters.

1. PUPPET MODULES:
AN HOLISTIC APPROACH
PuppetCamp Dublin 2012
Alessandro Franceschi

2. LAB 42
• 2007 - Meet Puppet. Managed the Bank of Italy webfarm
• 2008 - First generation of Lab42 Puppet Modules
• 2009 - Multi OS support and standardization of the modules
• 2010 - A redesigned and coherent Example42 Module set
Puppet Modules Standards and Interoperability (PuppetCamp Europe 2010 - Belgium)
Re-Use your Modules! (PuppetCamp 2010 - San Francisco)
• 2011 - Introducing Puppi
Puppi: Puppet strings to the shell (PuppetCamp Europe 2011 - Amsterdam)
• 2012 - Example42 Next Gen modules
Developing IT Infrastructures with Puppet (CodeMotion 2012 - Rome)

3. WE ALL LOVE
AND USE PUPPET FOR
• Systems Configuration
• (Automatic) Monitoring based on specific tools
• Facts based Inventory
• Manage, at times, Applications deployments
• Infrastructure Orchestration (coupled with MCollective)

4. WE LIKE
TO EXTEND PUPPET TO
• Abstract Automatic Monitoring (whatever the tool)
• Automatic Firewalling
• Standardize Applications deployments
• Enrich Systems Inventory
• Shell Extension (“Puppet Knowledge to the CLI”)
• Provide a coherent and integrated modules ecosystem

5. PUPPET MODULES MANTRAS
• Data Separation
• Configuration data is defined outside the module (or Puppet manifests)
• Module’s behavior is managed via APIs
• Reusability
• ReUse the same module in different shops
• Customize its behavior without changing its code
• Do not force how configurations are provided
• Standardization
• Follow PuppetLabs layout guidelines (puppet-lint)
• Have a coherent, predictable and intuitive interface
• Provide contextual documentation (puppet-doc)
• Interoperability
• Limit dependencies. Allow modules’ cherry picking
• Be self contained, do not interfere with other modules’ resources
• Cross Operating System support
• Provide sensible defaults for different OSes
• Allow easy implementation of support of new OSes

6. EXAMPLE42 NEXT GEN
• Coherent and Standardized structure
• Best Practices module design (with some tweaks...)
• Easily extendable Cross OS support
• Complete API exposure via parameters
• Extreme Customizations options
• Alternative Data Separation options
• Complete Decommissioning features
• Optional Automatic Monitoring Abstraction
• Optional Automatic Firewalling
• Optional Puppi support to enhance the CLI experience
• Exhaustive PuppetDoc documentation
• Integrated Rspec-Puppet tests
• Code Puppet-Lint compliant
• Quick module scaffolding based on different templates
... not exactly easy to read....

7. BASIC USAGE
• One Module. One Application. One main class.
• Install openssh with default settings:
class { 'openssh': }
• Equivalent to:
include openssh
• Default behavior:
• Install package
• Run and enable service
• Do not alter configurations

8. DATA INPUT ALTERNATIVES
• Set (top scope/ENC) variables and include classes:
$::openssh_template = 'site/openssh/openssh.conf.erb'
include openssh
• Use Hiera:
hiera(‘openssh_template’)
include openssh
• Use parametrized classes:
class { 'openssh':
template => 'site/openssh/openssh.conf.erb',
}
• Happily mix different patterns:
$::monitor = true
$::monitor_tool = [ 'nagios' , 'munin' , 'puppi' ]
class { 'openssh':
template => 'site/openssh/openssh.conf.erb',
}

9. DECOMMISSIONING
• Disable openssh service:
class { 'openssh':
disable => true
}
• Disable openssh service only at boot time:
class { 'openssh':
disableboot => true
}
• Remove openssh (package and files):
class { 'openssh':
absent => true
}
• Monitoring and firewalling resources removal is automatically
managed

10. MANAGE BEHAVIOR
• Enable Auditing:
class { 'openssh':
audit_only => true, # Default: false
}
(No changes to configuration files are made and what would be done is audited)
• Disable service autorestart:
class { 'openssh':
service_autorestart => false, # Default: true
}
(No automatic service restart when a configuration file / dir changes)
• Manage software version:
class { 'foo':
version => ‘1.2.0’, # Default: unset
}
Specify the package version you want to be installed.
Set => ‘latest’ to force installation of latest version

11. CUSTOMIZE: CONFIGURATION FILE
• Provide configuration as a static file ...
class { 'openssh':
source => ‘puppet:///modules/site/ssh/sshd.conf’,
}
• an array of files looked up on a first match logic ...
class { 'openssh':
source => ["puppet:///modules/site/ssh/sshd.conf-${fqdn}",
"puppet:///modules/site/ssh/openssh.conf"],
}
• As an erb template:
class { 'openssh':
template => ‘site/ssh/sshd.conf.erb’,
}
• Config File Path is defined in params.pp (can be overriden):
config_file = >’/etc/ssh/sshd_config’,

12. CUSTOM OPTIONS
• With templates you can provide an hash of custom options:
class { 'openssh':
template => ‘site/ssh/sshd.conf.erb’,
options => {
'LogLevel' => 'INFO',
'UsePAM' => 'yes',
},
}
• Alternative ways to use the options hash in an erb template:
• Direct but not safe (you must always provide all the used options)
UsePAM <%= options['UsePAM'] %>
• Failsafe with defaults (verbose but safe)
<% if scope.lookupvar("openssh::options['UsePAM']") then -%>
UsePAM <%= options['UsePAM'] %>
<% else -%>
UsePAM no
<% end -%>
• Show what you have (useful for config files has defaults for every option)
<% scope.lookupvar("openssh::options").sort_by {|key, value| key}.each do |key,
value| -%>
<%= key %> <%= value %>
<% end -%>

13. CUSTOMIZE: CONFIGURATION DIR
• You can manage the whole configuration directory:
class { 'openssh':
source_dir => ‘puppet:///modules/site/ssh/sshd/’,
}
This copies all the files in lab42/files/ssh/sshd/* to local config_dir
• Youcan purge any existing file on the destination config_dir
which are not present on the source_dir path:
class { 'openssh':
source_dir => ‘puppet:///modules/site/ssh/sshd/’,
source_dir_purge => true, # default is false
}
WARNING: Use with care
• Config Dir Path is defined in params.pp (can be overriden):
config_dir = >’/etc/ssh’,

14. CUSTOMIZE: CUSTOM CLASS
• Provide added resources in a custom class:
class { 'openssh':
my_class => ‘site/my_openssh’,
}
This autoloads: site/manifests/my_openssh.pp
• Custom class can have whatever you may need to add:
class site::my_openssh {
file { "motd":
path => "/etc/motd",
content => template("site/openssh/motd.erb"),
}
}
You hardly need to inherit openssh: there are parameters for everything
Do not call your class site::openssh, bad things may happen.

15. CUSTOMIZE: PATHS AND NAMES
• An example: Use the puppet module to manage pe-puppet!
class { 'puppet':
template => 'lab42/pe-puppet/puppet.conf.erb',
package => 'pe-puppet',
service => 'pe-puppet',
service_status => true,
config_file => '/etc/puppetlabs/puppet/puppet.conf',
config_file_owner => 'root',
config_file_group => 'root',
config_file_init => '/etc/sysconfig/pe-puppet',
process => ‘ruby’,
process_args => ‘puppet’,
process_user => ‘root’,
config_dir => '/etc/puppetlabs/puppet/',
pid_file => '/var/run/pe-puppet/agent.pid',
log_file => '/var/log/pe-puppet/puppet.log',
log_dir => '/var/log/pe-puppet',
}

16. EXTEND: MONITOR
• Manage automatic monitoring:
class { 'openssh':
monitor => true,
monitor_tool => [ ‘nagios’,‘puppi’,‘monit’ ],
monitor_target => $::ip_addess # Default
}
• Monitoring is based on parameters defined in params.pp:
port => ‘22’,
protocol => ‘tcp’,
service => ‘ssh[d]’, # According to OS
process => ‘sshd’,
process_args => ‘‘,
process_user => ‘root‘,
pid_file => ‘/var/run/sshd.pid’,
• Abstraction is managed in the Example42 monitor module
Here “connectors” for different monitoring tools are defined and can be added (also using 3rd
party modules).

17. EXTEND: FIREWALL
• Manage automatic firewalling (host based):
class { 'openssh':
firewall => true,
firewall_tool => ‘iptables’,
firewall_src => '10.0.0.0/8',
firewall_dst => $::ipaddress_eth1, # Default is $::ipaddress
}
• Firewallig is based on these parameters defined in params.pp:
port => ‘22’,
protocol => ‘tcp’,
• Abstraction is managed in the Example42 firewall module
Currently only the “iptables” firewall_tool is defined, it uses Example42 iptables module to
manage local iptables rules

18. EXTEND: PUPPI
• Manage Puppi integration:
class { 'openssh':
puppi => true, # Default: false
puppi_helper => ‘standard’ # Default
}
• The Puppi module is a prerequisite for all Example42 modules
Is required because it provides common libs, widely used in the modules
BUT the actual puppi integration is optional (and disabled by default)
• Puppi integration allows CLI enrichment commands like:
puppi info openssh
puppi log openssh
puppi check openssh
Note: puppi support for info/log commands for NextGen modules is under development
• Puppi helpers allow you to customize puppi behavior

19. PARAMS_LOOKUP EVERYWHERE
• Each parameter on NextGen class is passed via params_lookup
class openssh (
[...] # openssh module specific parameters ...
$my_class = params_lookup( 'my_class' ),
$source = params_lookup( 'source' ),
$source_dir = params_lookup( 'source_dir' ),
$source_dir_purge = params_lookup( 'source_dir_purge' ),
$template = params_lookup( 'template' ),
$service_autorestart = params_lookup( 'service_autorestart' , 'global' ),
$options = params_lookup( 'options' ),
$version = params_lookup( 'version' ),
$absent = params_lookup( 'absent' ),
$disable = params_lookup( 'disable' ),
$disableboot = params_lookup( 'disableboot' ),
$monitor = params_lookup( 'monitor' , 'global' ),
$monitor_tool = params_lookup( 'monitor_tool' , 'global' ),
$monitor_target = params_lookup( 'monitor_target' , 'global' ),
[...] # Other common parameters
) inherits openssh::params {
[...]
}
• Different kind of params that:
• Are module specific (no one defined in this openssh module)
• Allow customizations (my_class, source, template ...)
• Affect module’s behavior (absent, disable, service_autorestart, audit_only ...)
• Manage extensions (monitor, monitor_tool, firewall, puppi ...)
• Define application data (port, config_file, process, package ... )

20. PARAMS.PP
• Each module has a params class where defaults are set for different OS
class openssh::params {
### Application related parameters
$package = $::operatingsystem ? {
default => 'openssh-server',
}
$service = $::operatingsystem ? {
/(?i:Debian|Ubuntu|Mint)/ => 'ssh',
default => 'sshd',
}
$process = $::operatingsystem ? {
default => 'sshd',
}
[...]
$port = '22'
$protocol = 'tcp'
# General Settings
$my_class = ''
$source = ''
$source_dir = ''
$source_dir_purge = ''
[...]
### General module variables that can have a site or per module default
$monitor = false
$monitor_tool = ''
$monitor_target = $::ipaddress
$firewall = false
$firewall_tool = ''
$firewall_src = '0.0.0.0/0'
[...]
}

21. PARAMS_LOOKUP ORDER
• params_lookup is a function provided by the puppi module
• It allows data to be defined in different ways:
• Via Hiera, if available
• As Top Scope variable (as provided by External Node Classifiers)
• Via defaults set in the module’s params class
• The “global” argument is used to define site_wide behaviour
• Example:
class { ‘openssh’:
monitor => true
} # If there’s a direct param that’s the value, otherwise:
# If hiera is available:
hiera(“monitor”) # If global lookup is set
hiera(“openssh_monitor”) # A module specific value overrides the global one
# If variable is still not evaluated:
$::monitor # If global lookup is set
$::openssh_monitor # If present, overrides $::monitor
$openssh::params::monitor # Module’s predefined value is used as default

22. DOWNLOAD
• Example42 Puppet Modules Site: http://www.example42.com
• GitHub repositories: http://github.com/example42
• Download:
git clone -r http://github.com/example42/puppet-modules-nextgen
• Note on GitHub repos:
• puppet-modules-nextgen contains only NextGen modules
• puppet-modules contains both NextGen and older modules

23. ONE MORE THING...
• How to make a NextGen module
git clone -r http://github.com/example42/puppet-modules-nextgen
cd puppet-modules-nextgen
Example42-tools/module_clone.sh
This script creates a skeleton for a new module based on different Example42 foo module
templates. Run it from the directory that contains the foo module (moduledir).
By default it uses the "foo" module as template.
Specify -t <source_module> to use a different template.
Example:
Example42-tools/module_clone.sh -t foo_webapp
Source module template is foo
Enter the name of the new module based on foo: mynewmodule
E d i t my n e w m o d u l e / m a n i fe s t s / p a r a m s . p p t o m a n a g e s u p p o r t fo r d i f fe r e n t
OSes
•A new module (with the features seen so far) based on the
foo standard template is done. Add features and application /
OS specific resources to enrich it