301 lines
10 KiB
Markdown
301 lines
10 KiB
Markdown
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---
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layout: post
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title: 'Intro to Puppet: The Bare Minimum'
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tag:
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- puppet
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- technical
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---
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Last month, some of my coworkers were looking for a brief introduction to
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[Puppet](http://www.puppetlabs.com/). Puppet is a type of configuration manager
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for your servers. It allows you to create definitions of your server that can
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then be automatically maintained. Puppet is mostly self documenting so it makes
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it easy to know what your servers are doing while giving you a great way to
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automate setting up large numbers of servers.
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This is that brief talk. All code is available on
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[Github in my puppet-walkthru repository](https://github.com/atomaka/puppet-walkthru).
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You will need [Git](http://www.git-scm.com/),
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[Virtual Box](https://www.virtualbox.org/) and
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[Vagrant](http://www.vagrantup.com/) installed. To begin, clone the repository
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and launch the Vagrantfile:
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```
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git clone https://github.com/atomaka/puppet-walkthru.git
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cd puppet-walkthru
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vagrant up
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```
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This will setup a virtual machine on your computer with Puppet installed. All
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code can be found on the virtual machine in the /vagrant directory.
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```
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vagrant ssh
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sudo su cd /vagrant
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```
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You are now ready to work through the first example.
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## 1. Managing Users
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Puppet maintains state on your computer using what are referred to as
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[resources](http://docs.puppetlabs.com/references/latest/type.html). The
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built-in resources provided by Puppet provide a good start. In
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[example one](https://github.com/atomaka/puppet-walkthru/blob/master/manifests/1-user-type.pp),
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you can see how to use a Puppet resource to add and remove a user.
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```
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user { 'tm':
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ensure => present,
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}
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user { 'fowlks':
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ensure => absent,
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}
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```
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You can run this code on your virtual machine with
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`puppet apply manifests/1-user-type.pp`. Afterward, you should notice that the
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user "tm" exists on your system.
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The [user resource](http://docs.puppetlabs.com/references/latest/type.html#user)
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type manages local users on your system. This works on a wide variety of
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systems, although some do not support some of the more specific features. In
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this example, we make sure the user "tm" is present on the system and make sure
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the user "fowlks" is not present.
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ensure is a keyword for all Puppet resources. present and absent are the most
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common values although some resource types have others. ensure will make sure
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that definition exists on your server and absent will obviously do the opposite.
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## 2. Managing Files
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Managing files is one of the most common tasks for server administration and
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Puppet offers many ways to handle this. We’ll explore these in the
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[next example](https://github.com/atomaka/puppet-walkthru/blob/master/manifests/2-file-type.pp).
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```
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file { '/tmp/test1.txt':
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ensure => present,
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content => 'Hello',
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}
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file { '/tmp/test2.txt':
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ensure => present,
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source => '/vagrant/files/test2.txt',
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}
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$something = "Hello"
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file { '/tmp/test3.txt':
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ensure => present,
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content => template('/vagrant/templates/test3.txt.erb'),
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}
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```
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Run this on your virtual machine using `puppet apply manifests/2-file-type.pp`
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and you should be alerted that three files were created. You can verify this by
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viewing the contents of the tmp directory with `ls /tmp`.
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The first
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[file resource](http://docs.puppetlabs.com/references/latest/type.html#file)
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simply creates a file at the specified location that says "Hello."
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Unfortunately, this isn’t very useful since we do not want to have to type our
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entire cnfiguration file in our Puppet definition. The second resource is
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slightly more useful. This allows us to copy a file from our Puppet repository
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to a specified location.
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Finally, we can also create templates. The last example uses a file from our
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repository and copies it to the specified location. However, we can also include
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variables that can be used in our file. In this case, we set a variable to
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something and it is then displayed in the file: `You said: Hello`. The contents
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of `$something` are used in the file.
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## 3. Installing Packages
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The last common task we’ll look at is installing packages. Puppet provides a way
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to define which
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[packages](http://docs.puppetlabs.com/references/latest/type.html#package) can
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be installed. By default, this uses your distributions built-in package manager
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although there are ways to specify various providers. Our example
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[shows the most basic usage](https://github.com/atomaka/puppet-walkthru/blob/master/manifests/3-package-type.pp).
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```
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package { 'vim':
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ensure => present,
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}
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package { 'alpine-pico':
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ensure => absent,
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}
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```
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Try to open vim and you will notice it cannot run. Once you run this code with
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`puppet apply manifests/3-package-type.pp`, the vim package will then be
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present.
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## 4. Ordering (or lack thereof)
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The trickest thing for beginners to Puppet is dealing with its
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[non-deterministic behavior](http://puppetlabs.com/blog/inside-puppet-about-determinism).
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This is easier to
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[show than explain](https://github.com/atomaka/puppet-walkthru/blob/master/manifests/4-order-example.pp).
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```
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notify { 'First': }
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notify { 'Second': }
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notify { 'Third': }
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notify { 'Fourth': }
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notify { 'Fifth': }
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notify { 'Sixth': }
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notify { 'Seventh': }
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```
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When run, you would expect this to spit out First, Second, …, Seventh in order.
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Invoke this code with `puppet apply manifests/4-order-example.pp` and be
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surprised at the results. The order of the code is much different than what is
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in the file. Furthermore, if you were to add `notify { 'Eighth': }` the ordering
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might change completely.
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## 5. But I Need Order
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But there are dependencies when setting up systems. Puppet allows for this, you
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just are required to
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[explicitly define them](https://github.com/atomaka/puppet-walkthru/blob/master/manifests/5-ordered-example.pp).
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The biggest advantage here is that if one line of dependencies fails, your
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entire configuration does not. It takes some getting used to and can be
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frustrating, but it is worth it.
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```
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notify { 'First': }
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notify { 'Second':
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require => Notify['First'],
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}
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notify { 'Third':
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require => Notify['Second'],
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}
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notify { 'Fourth':
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require => Notify['Third'],
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}
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notify { 'Fifth':
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require => Notify['Fourth'],
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}
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notify { 'Sixth':
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require => Notify['Fifth'],
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}
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notify { 'Seventh':
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require => Notify['Sixth'],
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}
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```
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By using the `require` parameter, we have have forced ordering. If you run this
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code with `puppet apply manifests/5-ordered-example.pp`, you will see the order
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you expected in example number four.
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## 6. Know Your Environment
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Puppet also provides a way for you to know about the system that the Puppet code
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is running on with a system called Facter.
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```
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notify { "${::osfamily}": }
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notify { "${::ipaddress}": }
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notify { "${::uptime}": }
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```
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When run with `puppet apply manifests/6-facts-example.pp`,
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[this code](https://github.com/atomaka/puppet-walkthru/blob/master/manifests/6-facts-example.pp)
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will display the information about the virtual machine you are running on. We
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will look at why this is useful later.
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## 7. Doing Something Useful
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Now that we have seen some quick forced examples of how to use Puppet, we now
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have enough knowledge to do something that is actually useful. Using Puppet, we
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can
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[configure an entire service](https://github.com/atomaka/puppet-walkthru/blob/master/manifests/7-full-example.pp).
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If you are not familiar, [NTP](http://www.ntp.org/) is a networking protocol for
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time management. It is useful for mainitaining the same system time across all
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of your servers. And we can use Puppet to install it!
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```
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package { 'ntp':
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ensure => present,
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}
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file { '/etc/ntp.conf':
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ensure => present,
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require => Package['ntp'],
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source => '/vagrant/files/ntp.conf.debian',
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}
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service { 'ntp':
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ensure => running,
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enable => true,
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subscribe => File['/etc/ntp.conf'],
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}
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```
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When running this code with `puppet apply manifest/7-full-example.pp`, you
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should notice three things happen. First, the ntp package will be installed.
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Since we are on Ubuntu, this is done using apt-get. Secondly, a configuration
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file was copied from our Puppet repository to the location specified. Finally,
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the ntp service was started.
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Install, configure, start is one of the most common patterns in Linux/UNIX
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systems administration and we can easily automate it with Puppet.
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Something to note is our use of subscribe when using the
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[service resource](http://docs.puppetlabs.com/references/latest/type.html#service)
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type. This makes sure that the ntp service is restarted only if the
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configuration file has changed.
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## 7. Managing Multiple Operating Systems
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Before this section, be sure to reset what we did in the previous example by
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running bash support/cleanup7.sh. We just need to uninstall ntp and our config
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file so we can do it all again.
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Unfortunately, our environments are never uniform and we are stuck dealing with
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different versions of operating systems. Luckily, we have tools that we can use
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to deal with it. We touched on this in section six, but now we will actually use
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them
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[to install ntp again](https://github.com/atomaka/puppet-walkthru/blob/master/manifests/8-independent-example.pp).
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This time, our code will work on both Debian and RedHat family Linux
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distributions.
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```
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case $::osfamily {
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'RedHat': {
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$service = 'ntpd'
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$conf = 'ntp.conf.redhat'
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}
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'Debian': {
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$service = 'ntp'
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$conf = 'ntp.conf.debian'
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}
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}
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notify { 'OS Information':
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message => "${::osfamily}: Setting service to ${service} and conf to ${conf}",
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before => Package['ntp'],
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}
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package { 'ntp':
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ensure => present,
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}
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file { '/etc/ntp.conf':
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ensure => present,
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require => Package['ntp'],
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source => "/vagrant/files/${conf}",
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}
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service { $service:
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ensure => running,
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enable => true,
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subscribe => File['/etc/ntp.conf'],
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}
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```
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When on our Ubuntu virtual machine, running this code with
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`puppet apply manifest/8-independent-example.pp` will setup NTP just as we did
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in example seven. However, this code can also run on RedHat / CentOS machines
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without any adjustments.
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This is handled using the facts we discussed in section six. We check to see
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what distribution we are using with `$::osfamily` and make choices based on
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that. Since the service and the config file are different on RedHat, we assign
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variables to these and adjust them as needed.
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You now have enough knowledge to get started with Puppet!
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