thelinux.pro/_posts/2019-02-01-ruby-library-for-chef.md

layout	title	date	tags	excerpt	categories
post	Ruby Library for Chef	2019-02-01 16:30:00 -0500	ruby library libraries chef cookbook recipe bash mtime linux	Create a library for a Chef cookbook to drive consistency, efficiency, smaller file sizes	chef libraries ruby

One of the things that we can do to eliminate waste in code is to use libraries or functions so that we are not writing the same code over and over. This practice has many benefits, including:

1. Less typing
2. Consistency
3. Smaller file sizes
4. And more...

Exploring the cookbook

First, let's create a new cookbook. {% highlight bash %} $ chef generate cookbook test {% endhighlight %}

Change to the directory inside your new cookbook, and list the files

{% highlight bash %} $ ls

Berksfile CHANGELOG.md chefignore LICENSE metadata.rb README.md recipes spec test {% endhighlight %}

The folder we need doesn't exist yet, so let's create it:

{% highlight bash %} $ mkdir libraries {% endhighlight %}

Create a Library

For this post, we'll create a very simple library that will check the mtime (last time the file was modified, or touched)

Create a new file called mtime.rb in the libraries directory and add this to it:

{% highlight ruby %} def file_age(name) (Time.now - File.mtime(name))/(24*3600) end {% endhighlight %}

This code simply accepts a file name, then calculates it's age in days.

Use Your Library

Let's say we want Pulp to sync a repo every seven days... Create an attribute for the cadence by putting the following into attributes/default.rb

{% highlight ruby %} default['pulp-mirror']['sync']['cadence'] = 7 #In Days {% endhighlight %}

Then put in your recipe the following line attached to a code block:

{% highlight ruby %} action :sync if file_age("#{Chef::Config['file_cache_path']}/#{bag['id']}.sync") > node['pulp-mirror']['sync']['cadence'] {% endhighlight %}

Like this:

{% highlight ruby %} pulp_rpm_repo bag['id'] do display_name bag['display_name'] description bag['description'] feed bag['feed'] http bag['serve_http'] https bag['serve_https'] pulp_cert_verify false relative_url bag['relative_url'] action :sync if file_age("#{Chef::Config['file_cache_path']}/#{bag['id']}.sync") > node['pulp-mirror']['sync']['cadence'] end {% endhighlight %}