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書名： Puppet 2.7 Cookbook
作者名： John Arundel
本章字數： 481字
更新時間： 2021-04-02 18:19:59

Drawing dependency graphs

Dependencies can get complicated quickly, and it's easy to end up with a circular dependency (where A depends on B which depends on A) which will cause Puppet to complain and stop work. Fortunately, Puppet's --graph option makes it easy to generate a diagram of your resources and the dependencies between them, which can be a big help in fixing such problems.

Getting ready…

Install the graphviz package to view the diagram files as shown in the following code snippet:

# apt-get install graphviz

How to do it…

Create the file /etc/puppet/modules/admin/manifests/ntp.pp with the following code containing a circular dependency:

class admin::ntp {
    package { "ntp":
      ensure => installed,
      require => File["/etc/ntp.conf"],
    }

    service { "ntp":
      ensure  => running,
      require => Package["ntp"],
    }

    file { "/etc/ntp.conf":
      source  => "puppet:///modules/admin/ntp.conf",
      notify  => Service["ntp"],
      require => Package["ntp"],
    }
}

Copy your existing ntp.conf file into Puppet:

# cp /etc/ntp.conf /etc/puppet/modules/admin/files

Include this class on a node:
```
node cookbook {
  include admin::ntp
}
```

Run Puppet as follows:

# puppet agent --test
info: Retrieving plugin
info: Caching catalog for cookbook.bitfieldconsulting.com
err: Could not apply complete catalog: Found 1 dependency cycle: (File[/etc/ntp.conf] => Package[ntp] => File[/etc/ntp.conf]); try using the '--graph' option and open the '.dot' files in OmniGraffle or GraphViz
notice: Finished catalog run in 0.42 seconds

Run Puppet with the --graph option as suggested:
```
# puppet agent --test --graph
```

Check that the graph files have been created:

# ls /var/lib/puppet/state/graphs/
expanded_relationships.dot relationships.dot resources.dot

Create a graphic of the relationships graph:

# dot -Tpng -o relationships.png /var/lib/puppet/state/graphs/relationships.dot

View the graphic with the following command:
```
# eog relationships.png
```

How it works…

When you run puppet --graph (or enable the graph option in puppet.conf) Puppet will generate three graphs in DOT format (a graphics language).These are as follows:

resources.dot: shows the hierarchical structure of your classes and resources, but without dependencies
relationships.dot: shows the dependencies between resources as arrows, as in the preceding example
expanded_relationships.dot: is a more detailed version of the relationships graph

The dot tool (part of the graphviz package) will convert these to an image format such as PNG for viewing.

In the relationships graph, each resource in your manifest is shown as a balloon, with arrowed lines connecting them to indicate the dependencies. You can see that in our example, the dependencies between File["/etc/ntp.conf"] and Package["ntp"] form a circle.

To fix the circular dependency problem, all you need to do is remove one of the dependency lines and thus break the circle.

There's more…

Resource and relationship graphs can be useful even when you don't have a bug to find. If you have a very complex network of classes and resources, studying the resources graph can help you see where to simplify things. Similarly, when dependencies become too complicated to understand from reading the manifest, the graphs can be a much more useful form of documentation.

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Puppet 2.7 Cookbook

Drawing dependency graphs

Getting ready…

How to do it…

How it works…

There's more…