[chef] Re: postfix wrapper problem

[Daniel DeLeo < >]

On Thursday, April 3, 2014 at 1:52 PM, David Morton wrote:

> The postfix cookbook has all of its examples using roles to set various  
> attributes before running. I've seen a lot of push back on roles, and  
> was trying to make a wrapper cookbook, but there's a gotcha in attribute  
> loading order.
>  
> https://wiki.opscode.com/display/chef/Attributes+Cookbook says:
>  
> "When Chef loads cookbook attribute files, it does so in alphabetical  
> order for all the cookbooks. If you need to ensure that one attribute  
> file is loaded before another (for example, if your Apache cookbook  
> attributes requires that the Rails cookbook attributes are available  
> first) you can use the include_attribute method"
>  
> My wrapper cookbook starts with a "w" so the postfix cookbook comes  
> first. I can't add include_attribute to the postfix cookbook without  
> forking it, and adding include_attribute "postfix" in my own attributes  
> file after I set some defaults, doesn't work, because as I look at the  
> code for include_attribute, it explicitly ignores files it has already  
> loaded.

This documentation is wrong. 
http://docs.opscode.com/essentials_cookbook_attribute_files.html Is up to ;
date.

The gist of it is that does a deterministic topological sort (that also 
allows for circular dependencies) with the run list being the primary 
tiebreaker. In other words, chef iterates though your run_list, prepending 
each cookbook’s dependencies (and ignoring cookbooks already added to the 
sort order) to get a sane cookbook loading order. It then iterates through 
the cookbook-sorted list, loading the files in each cookbook. Alphabetical 
order is used on a per-cookbook basis to give you a stable, deterministic 
load order within a cookbook.

That said, this is still a problem with the wrapper cookbook pattern because 
wrapper_foo depends on foo, so foo gets loaded first. You have to either set 
all of the computed attributes yourself, or set your run_list so that it 
includes both wrapper_foo and then foo, in that order. Depending on how you 
manage your nodes’ run_lists that could be annoying, so you could maybe use a 
tiny role to encapsulate that.

--  
Daniel DeLeo