Support 'why-run' mode

[miketheman]

No description provided.

[miketheman]

On Chef 10.26.0, I get this:

$ sudo chef-client -W -Fdoc
...
Compiling Cookbooks...
Recipe: chef_handler::default
  * remote_directory[/var/chef/handlers] action createRecipe: <Dynamically Defined Resource>
  * cookbook_file[/var/chef/handlers/README] action create (up to date)
 (up to date)
Recipe: datadog::dd-handler
  * chef_gem[chef-handler-datadog] action install (up to date)
  * chef_handler[Chef::Handler::Datadog] action enable
    - Would load chef/handler/datadog
    - Would enable chef_handler[Chef::Handler::Datadog] as a report handler
    - Would enable chef_handler[Chef::Handler::Datadog] as a exception handler
Converging 419 resources
...
Recipe: datadog::repository
  * apt_repository[datadog] action add (up to date)
Recipe: <Dynamically Defined Resource>
  * execute[install-key C7A7DA52] action run (skipped due to not_if)
  * file[/var/lib/apt/periodic/update-success-stamp] action nothing (up to date)
  * execute[apt-cache gencaches] action nothing (up to date)
  * execute[apt-get update] action nothing (up to date)
  * file[/etc/apt/sources.list.d/datadog.list] action create (up to date)
Recipe: datadog::dd-agent
  * log[Running apt-get update to work around COOK-2171] action write (skipped due to not_if)
  * package[datadog-agent] action install (up to date)
  * directory[/etc/dd-agent] action create (up to date)
  * template[/etc/dd-agent/datadog.conf] action create (up to date)
  * service[datadog-agent] action enable (up to date)
  * service[datadog-agent] action start (up to date)
Recipe: datadog::network
  * datadog_monitor[network] action add (up to date)
Recipe: <Dynamically Defined Resource>
  * template[/etc/dd-agent/conf.d/network.yaml] action create (up to date)
Recipe: chef_handler::default
  * remote_directory[/var/chef/handlers] action nothing (up to date)
Recipe: datadog::dd-handler
  * chef_gem[chef-handler-datadog] action install (up to date)
  * chef_handler[Chef::Handler::Datadog] action nothing (up to date)
....

So I think we're good - we support running in why-run mode, and do not emit events/metrics during a why-run execution.

[olivielpeau]

Tested on Chef 12.2.1, the why-run execution seems to work fine (no changes to the state and no event/metrics emitted).

The only case I've found that doesn't work is the dd-handler recipe when the chef-handler-datadog gem is not installed. The run fails when 'chef/handler/datadog' is required here, with the following error:

  ================================================================================
  Recipe Compile Error in /home/vagrant/cookbooks/datadog/recipes/dd-handler.rb
  ================================================================================

  LoadError
  ---------
  cannot load such file -- chef/handler/datadog

  Cookbook Trace:
  ---------------
    /home/vagrant/cookbooks/datadog/recipes/dd-handler.rb:29:in `from_file'

(obviously because in why-run mode the chef_gem resource doesn't actually install the gem that's required)

But from what I understand this case is unavoidable.

[miketheman]

@olivielpeau Thanks for the investigation. Regarding the final case, this was reported a while back, and claimed to have been resolved. Might be worthwhile looking into it a bit further?

[olivielpeau]

@miketheman I think the issue you're mentioning is that the chef_gem resource itself breaks why-run mode, whereas here it's the subsequent require on chef/handler/datadog that's making the run fail when the file doesn't exist.

I'll look more into this issue (in particular I'll look at how chef_handler loads the handler's class and if that can help us solve this).

[miketheman]

@olivielpeau You're right - I linked the wrong issue.

Thinking about this further, there might be a better way to wrap the require that behaves differently based on whether or not we're in why-run mode, by inspecting the value of Chef::Config[:why_run].

Something maybe like:

if Chef::Config[:why_run]
  Chef::Log.warn('Running in why-run mode, skipping dd-handler')
  return
end

at the top of the recipe.

[olivielpeau]

@miketheman I like the idea of skipping dd-handler in why-run mode as I can't see any clean workaround to execute it in this mode.

FYI the 1.2.0 release of chef_handler allows using the handler without having to require it beforehand because it requires the handler's file on its own (see https://github.com/chef-cookbooks/chef_handler/blob/v1.2.0/providers/default.rb#L41), which would solve our issue here. The thing is that this version is only compatible with Chef >= 12 so we can't use it, but we should keep that in mind for the future.

Apart from that I think why-run mode is fully supported.

[miketheman]

Closed via #231