Daily Puppet - Virtual Resources

Virtual Resources are used when there is a need to have the same resource part of many classes.

Lets look at an example.

We have a user named "terry", who has to be part of two classes

1. test --> a very generic module for Ubuntu
2. testsql --> Another very generic module :), but applied to a different OS, CentOS

So, we define it first,

	class test::sysusers inherits test {
	user{'terry':
	ensure => present,
	uid => 4009,
	home => '/home/terry',
	shell => $shell,
	}
	}

view raw users hosted with ❤ by GitHub

This we will insert in two modules(manifests), test and testsql

	class test ($value=$test::params::value,
	$shell=$test::params::shell ) inherits test::params {
	include test::virtual
	contain test::config
	User <|title == 'minder'|>
	realize (User['hunter'])
	class test::sysusers
	}

view raw init.pp hosted with ❤ by GitHub

	class testsql {
	include ::test::virtual
	notify { "I am from the testsql":}
	class {'::test::sysusers': }
	}

view raw sqlinit.pp hosted with ❤ by GitHub

We have assigned "test" module assigned to centos server named centosserver, and "testsql" module assigned to a Ubuntu system named sqlserver1.

	node 'sqlserver1.labhome.com' {
	class { 'testsql':}
	}
	node 'centosserver.labhome.com' {
	class { 'test':}
	}

view raw site.pp hosted with ❤ by GitHub

We will run now run the puppet agent on both the systems

	[root@centosserver ~]# puppet agent -t
	Info: Retrieving pluginfacts
	Info: Retrieving plugin
	Info: Loading facts
	sh: dpkg: command not found
	Info: Caching catalog for centosserver.labhome.com
	Info: Applying configuration version '1440750961'
	Notice: /Stage[main]/Test::Sysusers/User[terry]/ensure: created
	Notice: Applied catalog in 0.14 seconds
	root@sqlserver1:/home/user# puppet agent -t
	Info: Retrieving pluginfacts
	Info: Retrieving plugin
	Info: Loading facts
	Error: Could not retrieve catalog from remote server: Error 400 on SERVER: Evaluation Error: Error while evaluating a Resource Statement, Duplicate declaration: Class[Test::Sysusers] is already declared; cannot redeclare at /etc/puppetlabs/code/environments/production/modules/testsql/manifests/init.pp:6 at /etc/puppetlabs/code/environments/production/modules/testsql/manifests/init.pp:6:2 on node sqlserver1.labhome.com
	Warning: Not using cache on failed catalog
	Error: Could not retrieve catalog; skipping run
	root@sqlserver1:/home/user#

view raw gistfile1.txt hosted with ❤ by GitHub

Refer to the error message for sqlserver1. It says "Error: Could not retrieve catalog from remote server: Error 400 on SERVER: Evaluation Error: Error while evaluating a Resource Statement, Duplicate declaration:"

To overcome this, we use virtual resources

	class test::sysusers inherits test {
	@user{'terry':
	ensure => present,
	uid => 5009,
	home => '/home/terry',
	shell => $shell,
	}
	}

view raw gistfile1.txt hosted with ❤ by GitHub

Look at the declaration, "@" with user, this indicates, the user resource declared is a virtual resource.

Now, we need to Realize the resource in init.pp in modules test and testsql , so that the resource is created on the target systems.

	cat modules/test/manifests/init.pp
	class test ($value=$test::params::value,
	$shell=$test::params::shell ) inherits test::params {
	include test::virtual
	include test::sysusers
	contain test::config
	User <|title == 'minder'|>
	realize (User['terry'])
	}
	cat modules/testsql/manifests/init.pp
	class testsql {
	include ::test::virtual
	include ::test::sysusers
	User <|title == 'minder'|>
	User <|title == 'wallander'|>
	User <|title == 'terry' |>
	notify { "I am from the testsql":}
	}

view raw gistfile1.txt hosted with ❤ by GitHub

From the snippet it can be seen that, realization is done in two ways,

a) realize (User['terry'])
b) User <|title == 'terry' |>

(Don't forget to include the class test::virtual in both the init.pp files, otherwise, we can not get the resource at all )

Now, we run the puppet agent on the clients again



With virtual resources, we can create user terry on both the systems.