Dynamic YAML config by processing ERB first

[nanliu]

The yaml configuration files are processed by ERB first. This allows
slightly more dynamic configs, such as support of environment variables
for vagrant vm/provisioner settings:

---
  provisioner:
    - type: puppet
      manifest_file: <%= ENV['VAGRANT_MANIFEST'] || 'init.pp' >

[nanliu]

Not sure if there's a better solution (or if I'm using this plugin wrong). This would allow something like:

---
  provisioner:
    - type: puppet
      manifest_file: <%= ENV['VAGRANT_MANIFEST'] || 'init.pp' >

[adrienthebo]

I would rather ERB interpolated YAML be implemented as a separate loader; the loader layer is entirely pluggable so you can easily implement elaborate loaders without having to change the core implementations.

[adrienthebo]

For that matter, you could add a custom loader that inherits from the YAML loader, override that one method, and be done with that. However I don't want this to be a core behavior of the YAML loader.

[nanliu]

Sure, I updated the PR.

[adrienthebo]

Also, one of the purposes of this plugin was to get away from intertwined logic and data. If you need functionality like this, why not use a stock Vagrantfile?

[nanliu]

Originally I was using a stock Vagrantfile, then I wrote a wrapper to simplify the VM specification, but it was a bit clunky. The more I updated the wrapper, the closer it looked like something like this, so I thought it would be easier to add a few small things to this project. I really don't need to tweak the rest of the VM configuration, except occasionally the puppet agent environment or the puppet manifest file name.

[Sharpie]

I also believe that one of the driving purposes behind config_builder is to provide a logic-less way of configuring Vagrant. However, thhat does not have to preclude having an ERB layer that re-introduces logic --- as long as the two remain clearly and cleanly separated into different loaders.

[nanliu]

Yep, the PR was rewritten so the erb loader is yaml_erb, and the original yaml loader is left as is.

[adrienthebo]

Okay, I'm 👍. Since this isn't as straightforward as pure YAML could you add some documentation to the class demonstrating the interpolation? Your first comment in this thread would be a great example of that.

[nanliu]

@adrienthebo, I've made some updates to the PR. Let me know what you think. I'll write another PR to update the project documentation (README, etc).

[adrienthebo]

Thanks for the contribution!