lab-09.1-Managing-file-content

Lab 9.1: Managing file content

Puppet file resources are useful when you need to manage a complete configuration file. Often, however, the resource we want to manage is actually represented by only a portion of a file. One such example is the host type. On most Linux systems, host entries are represented by a single line in the /etc/hosts file. Puppet doesn't know about all things that can be represented this way. One example is cron's allow and deny files, which describe which users can run jobs by listing their usernames in a file.

Your first task is to use the file_line resource type to ensure that root can run cron jobs. You will do this by ensuring that /etc/cron.allow has an entry for root and that /etc/cron.deny has a wildcard (*) to deny everyone not explicitly allowed. By managing parts of the file rather than the whole file, you leave the ability to allow access for other users intact.

Your second task is to iteratively build an /etc/motd file out of concat file fragments. Make sure to include a welcome message header.

Finally, if you choose to tackle the extra credit task, you will abstract the use of the concat::fragment resource type by defining your own type that simply accepts a message string and an order number.

To prevent resource contention, you will need to remove the review classification from your node group if you have not already done so.

Steps

1. Change directories to [modulepath]

   cd $(puppet agent --configprint environmentpath)/production/modules

2. Create a new module file_content

   pdk new module

3. You will see several questions requiring an answer. Enter the answers as you see below:

   Replace the N in studentN with your student number, e.g. student8

   Question	Answer
   Module Name	file_content
   Forge Name	studentN
   Credit author	Student N
   License	Apache-2.0
   Operating systems	RedHat

4. Create the file_content class.

   cd file_content
   pdk new class file_content
   

5. Edit manifests/init.pp

6. Add file_line resources to manage cron.allow and cron.deny.

7. Use a concat resource to manage /etc/motd.

8. Use concat::fragment resources to append messages to the motd.

   • Use templates to generate content if you'd like.

Test your module

1. Validate and test your new class

   pdk validate

2. Commit and deploy your codebase.

3. Classify your node with the file_content class.

4. Run puppet agent -t

5. Validate the results by inspecting /etc/motd

6. Run Puppet again and ensure no changes take place.

If you forgot to remove the review class, you might have noticed surprising behaviour or unexpected content in the /etc/motd file. This is because we are trying to manage the same file with two different resource types.

There are two common ways in which resource contention occurs. The more common is what we call flapping, because the same bits on disk are being managed by two different resource types. Puppet doesn't know about the overlap and attempts to make the file match the state definition in one of the declarations, and then make the file match the state definition of the other declaration. This results in the file content flapping back and forth between two states on every Puppet run.

The resource contention you're likely seeing here is due a quirk in the concat resource type that results in the concat resource simply overwriting the content of the file resource.

Extra Credit

Create a defined type that will allow other classes to register motd messages without needing to use the concat::fragment type. An example of using this type might look like:

file_content::motd { 'production warning':
    order   => 5,
    message => 'This is a production machine. Please make changes in Puppet instead.',
}

Solutions

Your module structure should resemble

[root@training modules]# tree file_content/
file_content/
├── examples
│   ├── init.pp
├── manifests
│   ├── init.pp
│   └── motd.pp (optional)
├── templates
    └── motd_header.epp

Example file: file_content/manifests/init.pp

class file_content {
  file { '/etc/cron.allow':
    ensure => file,
  }
  file_line { 'prevent cron jobs':
    ensure => present,
    path   => '/etc/cron.deny',
    line   => '*',
  }
  file_line { 'allow root cron jobs':
    ensure => present,
    path   => '/etc/cron.allow',
    line   => 'root',
  }
  concat { '/etc/motd':
    owner => 'root',
    group => 'root',
    mode  => '0644',
  }
  concat::fragment { 'motd header':
    target  => '/etc/motd',
    order   => '01',
    content => epp('file_content/motd_header.epp'),
  }
  concat::fragment { 'sample motd message':
    target  => '/etc/motd',
    order   => '50',
    content => "This is a sample motd message\n",
  }
}

Example file: file_content/examples/init.pp

include file_content

# extra credit declaration
file_content::motd { 'maintainer notice':
  message => "\n\n*** This machine is maintained by Wilson ***\n\n",
  order   => 5,
}

Example file: file_content/templates/motd_header.epp

Welcome to <%= $fqdn %>

This system is managed by Puppet. Any manual modifications will likely be
overwritten. Make configuration changes in the upstream repository.

Extra Credit Solution

Example file: file_content/manifests/motd.pp

define file_content::motd (
  $message = $name,
  $order   = 10,
) {
  concat::fragment { "motd fragment: ${name}":
    target  => '/etc/motd',
    order   => $order,
    content => $message,
  }
}

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