config: relax specification of Config.Volumes

Relaxes the specification of `Config.Volumes` by avoiding references to
the concept of "data volumes". Implementors are merely instructed to
provide mounts outside the container's root filesystem.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

config.md

@@ -148,8 +148,9 @@ Note: Any OPTIONAL field MAY also be set to null, which is equivalent to being a
 
    - **Volumes** *object*, OPTIONAL
 
-     A set of directories which SHOULD be created as data volumes in a container running this image.
-     If a file or folder exists within the image with the same path as a data volume, that file or folder will be replaced by the data volume and never be merged.
+     A set of directories describing where the process is likely write data specific to a container instance.
+     Implementations SHOULD provide mounts for these locations such that application data is not written to the container's root filesystem.
+     If a _new_ image is created from a container based on the image described by this configuration, data in these paths SHOULD NOT be included in the _new_ image.
      **NOTE:** This JSON structure value is unusual because it is a direct JSON serialization of the Go type `map[string]struct{}` and is represented in JSON as an object mapping its keys to an empty object.
 
    - **WorkingDir** *string*, OPTIONAL

specs-go/v1/config.go

@@ -37,7 +37,7 @@ type ImageConfig struct {
 	// Cmd defines the default arguments to the entrypoint of the container.
 	Cmd []string `json:"Cmd,omitempty"`
 
-	// Volumes is a set of directories which should be created as data volumes in a container running this image.
+	// Volumes is a set of directories describing where the process is likely write data specific to a container instance.
 	Volumes map[string]struct{} `json:"Volumes,omitempty"`
 
 	// WorkingDir sets the current working directory of the entrypoint process in the container.