Docker pull for image change comparison (#809)

* Moved logging to within docker_workspace and updated logic

* linter

* logging moved back to api.py, role.image modified if change detected

* fix to pass python unittests

* removing lauch.json that was commited by mistake

torchx/workspace/docker_workspace.py

@@ -105,6 +105,10 @@ def build_workspace_and_update_role(
             workspace: a fsspec path to a directory with contents to be overlaid
         """
 
+        old_imgs = [
+            image.id
+            for image in self._docker_client.images.list(name=cfg["image_repo"])
+        ]
         context = _build_context(role.image, workspace)
 
         try:
@@ -129,7 +133,8 @@ def build_workspace_and_update_role(
                     self.LABEL_VERSION: torchx.__version__,
                 },
             )
-            role.image = image.id
+            if len(old_imgs) == 0 or role.image not in old_imgs:
+                role.image = image.id
         finally:
             context.close()
 

torchx/workspace/test/docker_workspace_test.py

@@ -52,7 +52,7 @@ def test_docker_workspace(self) -> None:
 
             workspace = DockerWorkspaceMixin()
             workspace.build_workspace_and_update_role(
-                role, "memory://test_workspace", {}
+                role, "memory://test_workspace", {"image_repo": "example/repo_name"}
             )
 
             self.assertNotEqual("busybox", role.image)