[chef] Re: transactional recipe

[Sean OMeara < >]

Hi Daneel.

It's possible that Chef (or any other CM tool) may not be the best choice in tooling to do this.

That being said, it *totally is possible*. 

You'll want to create a custom resource type for this, (use the LWRP DSL), and implement the transactional logic in the provider. Always keep in mind that Chef is about ensuring state. "Test for state, take action to repair IF NEEDED"

The state you wish to ensure is "A directory exists inside an unmounted image".  

To pull this off, you'll need to mount the image, check for the directory, repair if needed, then clean up after yourself.

You'll need to do this on *every Chef run*.

Stating the problem like that, I'd personally choose focus on artifact generation using classic procedural scripting out of band of Chef.

If you do choose to implement this with a Chef provider, you'd want to start by thinking about the interface when using the custom resource. Something like this:

# somerecipe.rb

image_directory "example image" do

   path '/srv/images/blackbox.img'

   directory '/var/log/twiddlybits'

   action :create

end

If you want to use the LWRP DSL, the above example will need to be in cookbook named "image", 

If you'd rather use the full blown class interface (a so called HWRP), you can ship it in a cookbook with any name.

Either way, you'll want to implement the transactional logic in the provider, and you'll probably want to use mixlib::shellout to handle stdout.

Don't forget to call new_resource.updated_by_last_action(true) if you have to make the directory.

Good luck!

-s

On Mon, Nov 25, 2013 at 8:03 AM, Daneel Yaitskov < " target="_blank"> > wrote:

All,

I faced with complex relation between resources.

Let's look at this:

remote_file copies a disk image

execute losetup binds the image with a device

execute mount attaches the device to the filesystem

directory creates folder on the mounted image.

This recipe is not reliable because of an exception in a middle of the recipe
requires manual intervention to reset environment.

I.e. I should unmount the device because the first resource would write to mounted .

I could wrap all these resources inside of one ruby_block and use a lot nested begin/ensure
but then I lose any profit of the chef.

I want to preserve linear structure of the recipe and set rollback callbacks on successfully executed resources.

Is there any standard way?

--
Daneel S. Yaitskov