DevOps：Puppet，Docker，and Kubernetes
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Using resource defaults

A Puppet module is a group of related resources, usually grouped to configure a specific service. Within a module, you may define multiple resources; resource defaults allow you to specify the default attribute values for a resource. In this example, we'll show you how to specify a resource default for the File type.

How to do it...

To show you how to use resource defaults, we'll create an apache module. Within this module we will specify that the default owner and group are the apache user as follows:

  1. Create an apache module and create a resource default for the File type: 
      class apache {
    File {
      owner => 'apache',
      group => 'apache',
      mode => 0644,
    }
  }
  2. Create html files within the /var/www/html directory: 
      file {'/var/www/html/index.html':
    content => "<html><body><h1><a
      href='cookbook.html'>Cookbook!
      </a></h1></body></html>\n",
  }
  file {'/var/www/html/cookbook.html':
    content =>
      "<html><body><h2>PacktPub</h2></body></html>\n",
  }
  3. Add this class to your default node definition, or use puppet apply to apply the module to your node. I will use the method we configured in the previous chapter, pushing our code to the Git repository and using a Git hook to have the code deployed to the Puppet master as follows: 
    t@mylaptop ~/puppet $ git pull origin production
From git.example.com:repos/puppet
 * branch production -> FETCH_HEAD
Already up-to-date.
t@mylaptop ~/puppet $ cd modules
t@mylaptop ~/puppet/modules $ mkdir -p apache/manifests
t@mylaptop ~/puppet/modules $ vim apache/manifests/init.pp
t@mylaptop ~/puppet/modules $ cd ..
t@mylaptop ~/puppet $ vim manifests/site.pp 
t@mylaptop ~/puppet $ git status
On branch production
Changes not staged for commit:
modified: manifests/site.pp
Untracked files:
modules/apache/
t@mylaptop ~/puppet $ git add manifests/site.pp modules/apache
t@mylaptop ~/puppet $ git commit -m 'adding apache module'
[production d639a86] adding apache module
 2 files changed, 14 insertions(+)
 create mode 100644 modules/apache/manifests/init.pp
t@mylaptop ~/puppet $ git push origin production
Counting objects: 13, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (6/6), done.
Writing objects: 100% (8/8), 885 bytes | 0 bytes/s, done.
Total 8 (delta 0), reused 0 (delta 0)
remote: To puppet@puppet.example.com:/etc/puppet/environments/puppet.git
remote: 832f6a9..d639a86 production -> production
remote: Already on 'production'
remote: From /etc/puppet/environments/puppet
remote: 832f6a9..d639a86 production -> origin/production
remote: Updating 832f6a9..d639a86
remote: Fast-forward
remote: manifests/site.pp | 1 +
remote: modules/apache/manifests/init.pp | 13 +++++++++++++
remote: 2 files changed, 14 insertions(+)
remote: create mode 100644 modules/apache/manifests/init.pp
To git@git.example.com:repos/puppet.git
 832f6a9..d639a86 production -> production
  4. Apply the module to a node or run Puppet: 
    Notice: /Stage[main]/Apache/File[/var/www/html/cookbook.html]/ensure: defined content as '{md5}493473fb5bde778ca93d034900348c5d'
Notice: /Stage[main]/Apache/File[/var/www/html/index.html]/ensure: defined content as '{md5}184f22c181c5632b86ebf9a0370685b3'
Notice: Finished catalog run in 2.00 seconds
[root@hiera-test ~]# ls -l /var/www/html
total 8
-rw-r--r--. 1 apache apache 44 Sep 15 12:00 cookbook.html
-rw-r--r--. 1 apache apache 73 Sep 15 12:00 index.html

How it works...

The resource default we defined specifies the owner, group, and mode for all file resources within this class (also known as within this scope). Unless you specifically override a resource default, the value for an attribute will be taken from the default.

There's more...

You can specify resource defaults for any resource type. You can also specify resource defaults in site.pp. I find it useful to specify the default action for Package and Service resources as follows:

  Package { ensure => 'installed' }
  Service {
    hasrestart => true,
    enable     => true,
    ensure     => true,
  }

With these defaults, whenever you specify a package, the package will be installed. Whenever you specify a service, the service will be started and enabled to run at boot. These are the usual reasons you specify packages and services, most of the time these defaults will do what you prefer and your code will be cleaner. When you need to disable a service, simply override the defaults.

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