terraform: Adding resource provisioner interface

terraform/resource_provisioner.go

@@ -0,0 +1,28 @@
+package terraform
+
+// ResourceProvisioner is an interface that must be implemented by any
+// resource provisioner: the thing that initializes resources in
+// a Terraform configuration.
+type ResourceProvisioner interface {
+	// Validate is called once at the beginning with the raw
+	// configuration (no interpolation done) and can return a list of warnings
+	// and/or errors.
+	//
+	// This is called once per resource.
+	//
+	// This should not assume any of the values in the resource configuration
+	// are valid since it is possible they have to be interpolated still.
+	// The primary use case of this call is to check that the required keys
+	// are set and that the general structure is correct.
+	Validate(*ResourceConfig) ([]string, []error)
+
+	// Apply runs the provisioner on a specific resource and returns the new
+	// resource state along with an error. Instead of a diff, the ResourceConfig
+	// is provided since provisioners only run after a resource has been
+	// newly created.
+	Apply(*ResourceState, *ResourceConfig) (*ResourceState, error)
+}
+
+// ResourceProvisionerFactory is a function type that creates a new instance
+// of a resource provisioner.
+type ResourceProvisionerFactory func() (ResourceProvisioner, error)