[chef] Re: including recipes vs normal ruby require/include

[Daniel DeLeo < >]

On Thursday, February 16, 2012 at 7:09 AM, 

 
 wrote:

>  
> Chef folks,
>  
> I have a question about code reuse in Chef.
>  
> I know it’s not unusual for a recipe to include another recipe using the
> “include recipe” construct. But why is this better than using the normal
> Ruby mechanisms for code reuse? Couldn’t I organize my reusable bits of Chef
> code into ordinary Ruby modules, and then use the ordinary Ruby require and
> include tools to pull in the reusable bits as needed? My prejudice is to 
> stick
> to the normal Ruby way unless there's a compelling reason not to.
>  
> Jeff  
`include_recipe` contains chef-specific logic that Kernel.require and 
Kernel.load don't know about. For example, within a single chef run, you 
don't want to load duplicate recipes, so you want behavior similar to 
Kernel.require(). However, if you run chef as a daemon, you want that file to 
be loaded on the next chef run, which Kernel.require() will refuse to do, 
since it's already seen the file within the lifetime of the ruby process.

Also, recipe files are meant to be evaluated in a certain context. Resource 
declarations are looked up via method_missing to create resources in the 
resource collection. For this to work, recipes have to be evaluated in a 
context where the "recipe method_missing"[1] will be called. However, when 
you load a file with, say, Kernel.load(), the files are evaluated in the 
context of the main object. For example:

    ruby-1.9.3-p0 :003 > `cat /tmp/context.rb`
    => "puts self.inspect\n"  




    ruby-1.9.3-p0 :004 > o = Object.new
    => #<Object:0x007fc5c9880dd8>  
    ruby-1.9.3-p0 :005 > o.instance_eval { load "/tmp/context.rb" }
    main



Finally, be aware that while it's great that you can use ruby to get at 
Chef's internals and make it do things no one thought of before, the further 
you stray from the standard ways of doing things, the more likely you are to 
be broken by otherwise harmless changes.

HTH,

--  
Dan DeLeo


1. 
https://github.com/opscode/chef/blob/master/chef/lib/chef/mixin/recipe_definition_dsl_core.rb