I like Docker, but I’m not a huge fan of using shell scripts for complex system configuration…and Dockerfiles are basically giant shell scripts.

I was curious whether or not it would be possible to use Puppet during the docker build process. As a test case, I used the ssh module included in the openstack-puppet-modules package.

I started with a manifest like this (in puppet/node.pp):

class { 'ssh': }

And a Dockerfile like this:

I wanted to learn about writing custom Puppet types and providers. The official documentation is a little sparse, but I finally stumbled upon the following series of articles by Gary Larizza that provide a great deal of insight into the process and a bunch of example code:

• Fun With Puppet Providers
• Who Abstracted My Ruby?
• Seriously, What Is This Provider Doing?

I’ve been reading up on Puppet 3 lately, and came across the following:

XMLRPC was the new hotness when development on Puppet started. Now, XMLRPC is that horrible thing with the XML and the angle brackets and the pain and sad.

(from http://somethingsinistral.net/blog/the-angry-guide-to-puppet-3/)

…which also accurately sums up my feelings when I come across yet another piece of software where someone has decided that XML (or even JSON) is a good user-facing configuration syntax.

I note this here because it wasn’t apparent to me from the Puppet documentation.

If you have a Puppet class like this:

class foo {
  File {  ensure  => file,
          mode    => 600,
          }
}

And you use it like this:

class bar {
  include foo

  file { '/tmp/myfile': }
}

Then /tmp/myfile will not be created. But if instead you do this:

class bar inherits foo {
  file { '/tmp/myfile': }
}

It will be created with mode 0600. In other words, if you use inherits then definitions in the parent class are available in the scope of your subclass. If you include, then definitions in he included class are “below” the scope of the including class.