Learning Puppet III: Installing modules

In my previous post, we took a look at creating classes in Puppet and applying them locally. Let us look at installing Puppet modules next. Puppet does not install stdlib by default unlike other programming environments.

Common functionalities like reading a JSON file are part of stdlib module. It can often come in handy. Installing it is straightforward. However, after installation the modules are not loaded at run time.

Let us consider an example of reading a JSON file in a Puppet manifest. It can be an example of reading some config from an external resource.

Let us consider the module mod which we created in the previous post.

class mod::test_json{
      include mod

      $hash = loadjson('/tmp/load.json')
      [$message, $return_value] = $hash['output']
      notice("$message, $return_value")

}

To test, let us create a file at with the following content.

{
  "output": {
    "message": "The value is: ",
    "return_value": "0"
  }
}

To apply the manifest, we can try running the following:

puppet apply --modulepath=/path/to/parent/of/module -e "include mod::test_json"

This fails because loadjson is in stdlib. We need to enhance the module path to include stdlib as well. Modules are installed to the path /etc/puppetlabs/code/environments/production/modules. So, we need to modify our command as follows:

puppet apply --modulepath=/etc/puppetlabs/code/environments/production/modules:/vagrant/puppet -e "include elk::test_json"

Learning Puppet - II: Applying Classes

In my previous post about learning Puppet, I left a few open questions that I will attempt to answer as I continue learning.

1. How can I apply Puppet classes?
2. How can I install modules?
3. How can I define functions in Puppet?

In the last post, I was unable to apply a class so I moved ahead without it. Let us look at that in this post.

To apply a class, I created a module, created its init.pp file and added a class in it.

Let us consider the module name to be mod. The init.pp will be located at mod/manifests/init.pp. I just keep it empty to begin with. The name of the class in that file has to match the module name though.

class mod{
}

Moving on to create a class of interest, let us add one to install Openjdk. The file would be mod/manifests/jdk.pp.

class mod::jdk () {
  notice("Installing openJDK")
  # Install java
  package { 'openjdk':
    ensure => installed,
    name => 'java-1.8.0-openjdk-headless',
    alias => 'openjdk',
  }
}

To apply the manifest, the command would be as follows:

puppet apply --modulepath=/path/to/parent/of/module -e "include mod::jdk"