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書名： DevOps：Puppet，Docker，and Kubernetes
作者名： Thomas Uphill John Arundel Neependra Khare Hideto Saito Hui Chuan Chloe Lee Ke Jou Carol Hsu
本章字?jǐn)?shù)： 401字
更新時(shí)間： 2021-07-09 18:32:48

Installing, configuring, and starting a service

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.

How to do it...

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 httpd package:
```
  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.conf configuration file; the /etc/httpd/conf.d directory will not exist until the httpd package is installed. The require metaparameter tells Puppet that this file requires the httpd package 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.html file 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'],
  }

How it works…

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:

httpd will be running
The VirtualHost configuration file will exist
httpd will restart and be aware of the VirtualHost file
The DocumentRoot directory will exist
An index.html file will exist in the DocumentRoot directory

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