PuppetCamp NYC - Building Scalable Modules
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Transcript of PuppetCamp NYC - Building Scalable Modules
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Modules 201
Eric Shamow | PuppetCamp NYC
Writing Flexible and Scalable Puppet
Friday, April 27, 12
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Who Am I?
• Senior Professional Services Engineer for Puppet Labs
• Former Operations Manager
• Recovering Sysadmin
• Travel around helping people make Puppet even more awesome
• Not Shamwow. If you came to the wrong talk you can leave now
Friday, April 27, 12
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How Did We Get Here?
The module seemed just fine when I wrote it...
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How Did We Get Here?
The module seemed just fine when I wrote it...
(I never thought RHEL 6 would come out)
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I never thought...
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I never thought...
• RHEL 6 would come out
Friday, April 27, 12
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I never thought...
• RHEL 6 would come out
• My company would switch to Debian
Friday, April 27, 12
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I never thought...
• RHEL 6 would come out
• My company would switch to Debian
• Other people would want to reuse the module
Friday, April 27, 12
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I never thought...
• RHEL 6 would come out
• My company would switch to Debian
• Other people would want to reuse the module
• I’d want to use only a part of the module
Friday, April 27, 12
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I never thought...
• RHEL 6 would come out
• My company would switch to Debian
• Other people would want to reuse the module
• I’d want to use only a part of the module
• ...maybe as a part of something else
Friday, April 27, 12
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Ur Doin It Wrong
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Puppet is DeclarativeShoehorning conditional logic into
declarative language?
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Puppet is DeclarativeShoehorning conditional logic into
declarative language?
Please do not do this:
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Puppet is DeclarativeShoehorning conditional logic into
declarative language?
Please do not do this:case $::operatingsystem { ‘redhat’: { if $::fqdn == “bobmarley” { file { ‘foo’: ... } else { ... ...}
Friday, April 27, 12
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When Logic Fails
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Organizing Your Data
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Organizing Your Data
• Hiera
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Organizing Your Data
• Hiera
• External Node Classifiers
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Organizing Your Data
• Hiera
• External Node Classifiers
• Custom Functions
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Code Models Reality
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Code Models Reality
• Move complexity closer to where it is in real life
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Code Models Reality
• Move complexity closer to where it is in real life
• If your CMDB contains lots of exceptions, that’s where you should read from
Friday, April 27, 12
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Code Models Reality
• Move complexity closer to where it is in real life
• If your CMDB contains lots of exceptions, that’s where you should read from
• If there is contorted logic, keep it away from nuts and bolts module mechanics
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Please Don’t Make Me Edit Your Module
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Parameterized Classes
class motd ( $pci_enabled = true, $owner = ‘bob’,) { ...}
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params.pp Pattern
class motd::params { $owner = ‘Bob’}
class motd ( $owner = $motd::params::owner) {
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params.pp Pattern + hiera
class motd::params { $owner = hiera(‘owner’,‘Bob’)}
class motd ( $owner = $motd::params::owner) {
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Outsource Logic to Submodules
class mysql::params { $server_package = $::operatingsystem ? { ‘redhat’ => ‘mysql-server’, ... }}
class mysql::server { package { ‘mysql-server’: name => $mysql::params::server_package, ... }}
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Be as Modular as Possible
class mysql::server { package { ‘mysql-server’: name => $mysql::params::server_package, ... }}class mysql::client { ...}class mysql { include mysql::client include mysql::server}
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Limit Inheritance
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Limit Inheritance
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Limit Inheritance
• Favor composition over inheritance
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Limit Inheritance
• Favor composition over inheritance
• Inheritance + dynamic variable scoping = PAIN
Friday, April 27, 12
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Limit Inheritance
• Favor composition over inheritance
• Inheritance + dynamic variable scoping = PAIN
• Useful at the edges
Friday, April 27, 12
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Limit Inheritance
• Favor composition over inheritance
• Inheritance + dynamic variable scoping = PAIN
• Useful at the edges
• Useful for overriding/extending in limited circumstances
Friday, April 27, 12
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Stop Being Surprised by Change
Friday, April 27, 12
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Stop Being Surprised by Change
Friday, April 27, 12
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• You don’t have to define every Operating System or version
Stop Being Surprised by Change
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• You don’t have to define every Operating System or version
• Assume cutovers won’t be clean - you will be 50% RHEL 5 and 50% RHEL 6 for a while
Stop Being Surprised by Change
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• You don’t have to define every Operating System or version
• Assume cutovers won’t be clean - you will be 50% RHEL 5 and 50% RHEL 6 for a while
• And even when you aren’t, you’ll be 98% RHEL 6 and 2% RHEL 5 until the end of time.
Stop Being Surprised by Change
Friday, April 27, 12
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Protect Yourself Against Unintentional Defaults
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• Always provide a default case
Protect Yourself Against Unintentional Defaults
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• Always provide a default case
• In most cases that default case should be failure
Protect Yourself Against Unintentional Defaults
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• Always provide a default case
• In most cases that default case should be failure
• Use the stdlib :fail method to fail gracefully.
Protect Yourself Against Unintentional Defaults
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Protect Yourself Against Unintentional Defaults
class mysql::params { case $::operatingsystem { ‘redhat’: { $serverpkg = ‘mysql-server’ } default: { fail(‘MySQL Server package undefined.’) } }}
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RememberYou Don’t Have To Think of
Everything
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RememberYou Don’t Have To Think of
Everything
Leave room for others to improve your modules without refactoring them...
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RememberYou Don’t Have To Think of
Everything
Leave room for others to improve your modules without refactoring them...
...and then you get to benefit and re-merge their changes when they do.
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And then we haz a community!
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