Love / Hate Puppet (Puppet Gotchas)

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This document discusses the author's experience with Puppet, including things they love and find interesting about it. The author notes some inconsistent type casting and equality behaviors in Puppet that can be confusing. They also discuss how exported resources and Hiera allow Nagios and DNS configuration to be automated easily and remove hard-coded data from Puppet code for improved reusability. The author concludes by praising Puppet's capabilities around automation, abstraction, repeatability, reporting and knowledge management.

Technology

Love / Hate Puppet
Stephen Johnson
Stephen@puppetlabs.com

Background

• Puppetlabs employ for a a year
• I have been using Puppet since 0.24
• Currently working on the hiera_debug and
rseencﬁle projects

What is this

• Its not a puppet bashing
• Interesting Puppet behavior
• What i love about puppet

Interesting Behavior

• Type Casting
• Type Equality
• Inconsistencies
• Scoping

Type Casting (FTW)

• $wibble = “3” (String)
• $wibble2 = “2” (String)
• $wtf = $wibble + wibble2 ?

Type Equality

• $wibble = '3'
• $wibble2 = '2'
• $wibble3 = $wibble + $wibble2
• $wibbletest = 5
• is $wibble3 == $wibbletest

Type Equality 2

• $wibble = ‘true’
• $wibble2 = true
• is $wibble == $wibble2

Type Equality 3

• $wibble = 0
• $wibble2 = -1
• are they equal to true

Type Equality

• There are many many more
• Be careful with data lookups from hiera

Noop on class

• class{'testtwo': noop => true ;}
• All the resources are noop surely

Scoping

• Thank good for 3.0
• Removing dynamic scoping

2.7

• Dynamic scoping is very very very
dangerous
• Always use full scoped values

3.0

• It has been removed
• Full scope variables

Facts
• Top level variables
• Do not trust them as sent from client
• Dont use if $::hostname ==
• Export FACTER_hostname=‘puppetmaster’
• puppet agent -t
• See my blog on thatbytes.co.uk

Is not all bad

• All languages have interesting behavior
• Look at the famous “WAT’ talk from Gary
Bernhardt
• www.destroyallsoftware.com/talks/wat

What i love

• Exported Resources
• Puppet
• Hiera

Exported Resources

• Nagios is so hard to setup all those conﬁg
ﬁles
• Dns is so hard we have to track all those ip
address

Nagios Automated

• Nagios
node
webserver
{

@@file
{
"/etc/nagios/conf.d/$::fqdn.apachecheck.conf":

content
=>
"nagios
check
stuff
n",

tag
=>
"nagioscheck",

}

}

node
nagiosmachine
{

File
<<|
tag
==
'nagioscheck'
|>>

}

Export the resource

• @@file
{
"/etc/nagios/conf.d/$::fqdn.apachecheck.conf":

content
=>
template(‘apache/nagioscheck.erb’),

tag
=>
"nagioscheck",

}

• Tagged with nagioscheck
• Have a apache::nagios class ?

Collect the resource

File
<<|
tag
==
'nagioscheck'
|>>

• Using the tag previously
• In your nagios::server class

How does that work

• Puppetdb
• Stores conﬁgs
• Scalable
• AWESOMENESS

Puppet

• Automation
• Abstraction
• Repeatable
• Reportable
• AWESOMEABLE

Puppet gets you
Knowledge
• Version controlled infrastructure
• Convergence
• Reporting
• Query-ability
• Removing the snowﬂakes

Hiera

• Puppet modules without hard-coded data
are easily shared and more re-usable
• Infrastructure conﬁguration can be
managed without needing to edit Puppet
code
• The data problem

Bad Data
if ( $::environment == ‘dev’ ) {
$ntpserver = ‘192.168.2.1’
} else {
if ( $::fqdn == ‘host4.mycorp.com’) {
$ntpserver = ‘127.0.0.1’
} else {
$ntpserver = ‘213.21.6.4’
}
}

Good Data
$ntpserver = hiera(‘ntpserver’)

:hierarchy:

- %{operatingsystem}

- %{environment}

- %{fqdn}

- common

Remove Data from
Code
• Hiera uses information to determine a
hierarchy
• Top down hierarchy for overriding
conﬁguration values based on roles,
environments, locations.... or anything else
• And do this without any coding!

Puppet 3.0

• Hiera is integrated into the core product
• Introduces data mapping for parameterized classes
• Backwards compatible

Hiera

• What where the variables
• How looked the variables up

Learn more

• git://github.com/nfagerlund/evil-made-
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