Improve encapsulation power of juju_integration to avoid leaking implementation detail

[sed-i]

Requirements

Let's say we have two apps to deploy,

resource "juju_application" "some_app" {
  name  = "some-app"
  model = local.model_name

  charm {
    name    = "my-charm"
    channel = var.channel
    base    = "[email protected]"
  }
  units  = 1
}


module "bundle" {
  source     = "git::https://github.com/canonical/bundle//terraform"
  model_name = local.model_name
  channel    = local.channel
}

To create a juju integration, we must provide the application Block Set verbatim:

resource "juju_integration" "some-app-bundle" {
  model = local.model_name

  application {
    name     = module.bundle.app_name
    endpoint = module.bundle.my_endpoint
  }

  application {
    name     = juju_application.some_app.app_name
    endpoint = "some-endpoint"
  }
}

Ideally, module.bundle would offer its side of an integration in its entirety, without the user needing to know the implementation detail of the underlying charms:

resource "juju_integration" "some-app-bundle" {
  model = local.model_name

  module.bundle.my_endpoint

  application {
    name     = juju_application.some_app.app_name
    endpoint = "some-endpoint"
  }
}

• Afaict, this is not supported by terraform?
• Should we adjust the juju_integration interface to improve encapsulation?

Urgency

It would save from a weird workaround.
Currently, the implementation of juju_integration forces us to leak implementation detail.

Notes & References

No response

[hmlanigan]

@sed-i

I'd expect the following to work provided both apps have matching provided and required endpoint names as with juju integrate module.bundle.app_name juju_application.some_app.app_name:

resource "juju_integration" "some-app-bundle" {
  model = local.model_name

  application {
    name     = module.bundle.app_name
  }

  application {
    name     = juju_application.some_app.app_name
  }
}

Only if juju cannot disambiguate the endpoints should it be necessary to specify them. For the two example applications, is that the choice?

As to your suggestion of the application block being exported by the bundle module, that sounds like question for a terraform expert and not specific to the juju provider. It has no control over how terraform interprets didn't input into the different resources.