add support for jetter to Role (base_image) for mast launches

torchelastic/tsm/driver/api.py

@@ -92,6 +92,17 @@ class Container:
     A ``Resource`` can be bound to a specific scheduler backend or ``SchedulerBackend.ALL`` (default)
     to specify that the same ``Resource`` is to be used for all schedulers.
 
+    An optional ``base_image`` can be specified if the scheduler supports a
+    concept of base images. For schedulers that run Docker containers the
+    base image is not useful since the application image itself can be
+    built from a base image (using the ``FROM base/image:latest`` construct in
+    the Dockerfile). However the base image is useful for schedulers that
+    work with simple image artifacts (e.g. ``*.tar.gz``) that do not have a built-in
+    concept of base images. For these schedulers, specifying a base image that
+    includes dependencies while the main image is the actual application code
+    makes it possible to make changes to the application code without incurring
+    the cost of re-building the uber artifact.
+
     Usage:
 
     ::
@@ -106,9 +117,13 @@ class Container:
                        .require(Resource(cpu=1, gpu=1, memMB=500), "custom_scheduler")
                        .ports(tcp_store=8080, tensorboard=8081)
 
+    # for schedulers that support base_images
+    my_container = Container(image="my/trainer:1", base_image="common/ml-tools:latest")
+                      .require(...)
     """
 
     image: str
+    base_image: Optional[str] = None
     resources: Resource = NULL_RESOURCE
     port_map: Dict[str, int] = field(default_factory=dict)
 
@@ -130,6 +145,9 @@ def ports(self, **kwargs: int) -> "Container":
 # sentinel value used to represent missing string attributes, such as image or entrypoint
 MISSING: str = "<MISSING>"
 
+# sentinel value used to represent "unset" optional string attributes
+NONE: str = "<NONE>"
+
 # sentinel value used as the "zero" element in the container group
 NULL_CONTAINER: Container = Container(image=MISSING)
 
@@ -141,9 +159,11 @@ class macros:
 
     Available macros:
 
-    1. ``img_root`` - root directory of the pulled image on the container
-    2. ``app_id`` - application id as assigned by the scheduler
-    3. ``replica_id`` - unique id for each instance of a replica of a Role,
+    1. ``img_root`` - root directory of the pulled conatiner.image
+    2. ``base_img_root`` - root directory of the pulled container.base_image
+                           (resolves to "<NONE>" if no base_image set)
+    3. ``app_id`` - application id as assigned by the scheduler
+    4. ``replica_id`` - unique id for each instance of a replica of a Role,
                         for instance a role with 3 replicas could have the 0, 1, 2
                         as replica ids. Note that when the container fails and is
                         replaced, the new container will have the same ``replica_id``
@@ -163,15 +183,25 @@ class macros:
     """
 
     img_root = "${img_root}"
+    base_img_root = "${base_img_root}"
     app_id = "${app_id}"
     replica_id = "${replica_id}"
 
     @staticmethod
-    def substitute(args: List[str], img_root: str, app_id: str, replica_id: str):
+    def substitute(
+        args: List[str],
+        img_root: str,
+        app_id: str,
+        replica_id: str,
+        base_img_root: str = NONE,
+    ):
         args_sub = []
         for arg in args:
             sub = Template(arg).safe_substitute(
-                img_root=img_root, app_id=app_id, replica_id=replica_id
+                img_root=img_root,
+                app_id=app_id,
+                replica_id=replica_id,
+                base_img_root=base_img_root,
             )
             args_sub.append(sub)
         return args_sub
@@ -419,8 +449,6 @@ def is_terminal(state: AppState) -> bool:
     return state in _TERMINAL_STATES
 
 
-NONE: str = "<NONE>"
-
 # =======================
 # ==== Status API =======
 # =======================