load_cache or similar support

[matiasanaya]

I want to know if it's possible to use a get resource instead of pulling down the image when cache: true is set for building.

Say this is my current job (which has the nice benefit that the FROM image can be cached by concourse):

- get: repo
- get: a-cached-docker-image-from
  params: { save: true }
- put: a-docker-image
      get_params: { skip_download: true }
      params:
        build: repo
        cache: true
        cache_tag: a-cached-tag
        load_base: a-cached-docker-image-from

I'd like for something like the following to work equivalently (where the cache image can be cached by concourse):

- get: repo
- get: a-cached-docker-image
  params: { save: true }
- get: a-cached-docker-image-from
  params: { save: true }
- put: a-docker-image
      get_params: { skip_download: true }
      params:
        build: repo
        load_cache: a-cached-docker-image # this does not exist
        load_base: a-cached-docker-image-from

[jtarchie]

I'm pretty confused. What would the difference in load_base and load_cache? Wouldn't they just both be loading the layers from an image? Why do you need both?

[matiasanaya]

@jtarchie did I get it wrong? The way I understand it load_base will be used as the FROM ... image while cache: true is using a resulting image in hopes it can re-use a layer. load_cache would basically allow for those layers to be populated. Maybe a solution with only one attribute which takes an array would do. i.e.

load_layers:
  - a-cached-docker-image
  - a-cached-docker-image-from

[jtarchie]

No, I just don't understand docker that well. There are too many layers to it.

Thanks for the explanation. I think there might be a way to do what you are requesting. I believe others have done it.

[matiasanaya]

Fixed by #188