feat(framework) Introduce --isolation flag for flower-superlink (#…

…4354)

src/py/flwr/server/app.py

@@ -42,6 +42,8 @@
     FLEET_API_GRPC_BIDI_DEFAULT_ADDRESS,
     FLEET_API_GRPC_RERE_DEFAULT_ADDRESS,
     FLEET_API_REST_DEFAULT_ADDRESS,
+    ISOLATION_MODE_PROCESS,
+    ISOLATION_MODE_SUBPROCESS,
     MISSING_EXTRA_REST,
     TRANSPORT_TYPE_GRPC_ADAPTER,
     TRANSPORT_TYPE_GRPC_RERE,
@@ -634,6 +636,19 @@ def _add_args_common(parser: argparse.ArgumentParser) -> None:
         "to create a secure connection.",
         type=str,
     )
+    parser.add_argument(
+        "--isolation",
+        default=ISOLATION_MODE_SUBPROCESS,
+        required=False,
+        choices=[
+            ISOLATION_MODE_SUBPROCESS,
+            ISOLATION_MODE_PROCESS,
+        ],
+        help="Isolation mode when running a `ServerApp` (`subprocess` by default, "
+        "possible values: `subprocess`, `process`). Use `subprocess` to configure "
+        "SuperLink to run a `ServerApp` in a subprocess. Use `process` to indicate "
+        "that a separate independent process gets created outside of SuperLink.",
+    )
     parser.add_argument(
         "--database",
         help="A string representing the path to the database "