There are many examples of this pattern online. In our simple example, we will create an Apache configuration file under /etc/httpd/conf.d/cookbook.conf. The /etc/httpd/conf.d directory will not exist until the httpd package is installed. After this file is created, we would want httpd to restart to notice the change; we can achieve this with a notify parameter.
We will need the same definitions as our last example; we need the package and service installed. We now need two more things. We need the configuration file and index page (index.html) created. For this, we follow these steps:
As in the previous example, we ensure the service is running and specify that the service requires the
httpdpackage:service {'httpd': ensure => running, require => Package['httpd'], }We then define the package as follows:
package {'httpd': ensure => installed, }Now, we create the
/etc/httpd/conf.d/cookbook.confconfiguration file; the/etc/httpd/conf.ddirectory will not exist until thehttpdpackage is installed. Therequiremetaparameter tells Puppet that this file requires thehttpdpackage to be installed before it is created:file {'/etc/httpd/conf.d/cookbook.conf': content => "<VirtualHost *:80>\nServernamecookbook\nDocumentRoot/var/www/cookbook\n</VirtualHost>\n", require => Package['httpd'], notify => Service['httpd'], }We then go on to create an
index.htmlfile for our virtual host in/var/www/cookbook. This directory won't exist yet, so we need to create this as well, using the following code:file {'/var/www/cookbook': ensure => directory, } file {'/var/www/cookbook/index.html': content => "<html><h1>Hello World!</h1></html>\n", require => File['/var/www/cookbook'], }
The require attribute to the file resources tell Puppet that we need the /var/www/cookbook directory created before we can create the index.html file. The important concept to remember is that we cannot assume anything about the target system (node). We need to define everything on which the target depends. Anytime you create a file in a manifest, you have to ensure that the directory containing that file exists. Anytime you specify that a service should be running, you have to ensure that the package providing that service is installed.
In this example, using metaparameters, we can be confident that no matter what state the node is in before running Puppet, after Puppet runs, the following will be true: