Create server-side compatibility package (#2957)

e2e/bare-https/driver.py

@@ -3,7 +3,7 @@
 
 
 # Start Flower server
-hist = fl.server.driver.start_driver(
+hist = fl.server.start_driver(
     server_address="127.0.0.1:9091",
     config=fl.server.ServerConfig(num_rounds=3),
     root_certificates=Path("certificates/ca.crt").read_bytes(),

e2e/bare/driver.py

@@ -2,7 +2,7 @@
 
 
 # Start Flower server
-hist = fl.server.driver.start_driver(
+hist = fl.server.start_driver(
     server_address="0.0.0.0:9091",
     config=fl.server.ServerConfig(num_rounds=3),
 )

e2e/fastai/driver.py

@@ -1,6 +1,6 @@
 import flwr as fl
 
-hist = fl.server.driver.start_driver(
+hist = fl.server.start_driver(
     server_address="0.0.0.0:9091",
     config=fl.server.ServerConfig(num_rounds=3),
 )

e2e/jax/driver.py

@@ -1,6 +1,6 @@
 import flwr as fl
 
-hist = fl.server.driver.start_driver(
+hist = fl.server.start_driver(
     server_address="0.0.0.0:9091",
     config=fl.server.ServerConfig(num_rounds=3),
 )

e2e/opacus/driver.py

@@ -1,6 +1,6 @@
 import flwr as fl
 
-hist = fl.server.driver.start_driver(
+hist = fl.server.start_driver(
     server_address="0.0.0.0:9091",
     config=fl.server.ServerConfig(num_rounds=3),
 )

e2e/pandas/driver.py

@@ -3,7 +3,7 @@
 from strategy import FedAnalytics
 
 # Start Flower server
-hist = fl.server.driver.start_driver(
+hist = fl.server.start_driver(
     server_address="0.0.0.0:9091",
     config=fl.server.ServerConfig(num_rounds=1),
     strategy=FedAnalytics(),

e2e/pytorch-lightning/driver.py

@@ -1,6 +1,6 @@
 import flwr as fl
 
-hist = fl.server.driver.start_driver(
+hist = fl.server.start_driver(
     server_address="0.0.0.0:9091",
     config=fl.server.ServerConfig(num_rounds=3),
 )

e2e/pytorch/driver.py

@@ -18,7 +18,7 @@ def weighted_average(metrics: List[Tuple[int, Metrics]]) -> Metrics:
 strategy = fl.server.strategy.FedAvg(evaluate_metrics_aggregation_fn=weighted_average)
 
 # Start Flower server
-hist = fl.server.driver.start_driver(
+hist = fl.server.start_driver(
     server_address="0.0.0.0:9091",
     config=fl.server.ServerConfig(num_rounds=3),
     strategy=strategy,

e2e/scikit-learn/driver.py

@@ -36,7 +36,7 @@ def evaluate(server_round, parameters: fl.common.NDArrays, config):
         evaluate_fn=get_evaluate_fn(model),
         on_fit_config_fn=fit_round,
     )
-    hist = fl.server.driver.start_driver(
+    hist = fl.server.start_driver(
         server_address="0.0.0.0:9091",
         strategy=strategy,
         config=fl.server.ServerConfig(num_rounds=3),

e2e/tabnet/driver.py

@@ -1,6 +1,6 @@
 import flwr as fl
 
-hist = fl.server.driver.start_driver(
+hist = fl.server.start_driver(
     server_address="0.0.0.0:9091",
     config=fl.server.ServerConfig(num_rounds=3),
 )

e2e/tensorflow/driver.py

@@ -18,7 +18,7 @@ def weighted_average(metrics: List[Tuple[int, Metrics]]) -> Metrics:
 strategy = fl.server.strategy.FedAvg(evaluate_metrics_aggregation_fn=weighted_average)
 
 # Start Flower server
-hist = fl.server.driver.start_driver(
+hist = fl.server.start_driver(
     server_address="0.0.0.0:9091",
     config=fl.server.ServerConfig(num_rounds=3),
     strategy=strategy,

examples/quickstart-cpp/driver.py

@@ -3,7 +3,7 @@
 
 # Start Flower server for three rounds of federated learning
 if __name__ == "__main__":
-    fl.server.driver.start_driver(
+    fl.server.start_driver(
         server_address="0.0.0.0:9091",
         config=fl.server.ServerConfig(num_rounds=3),
         strategy=FedAvgCpp(),

src/py/flwr/server/__init__.py

@@ -18,12 +18,13 @@
 from . import driver, strategy
 from .app import run_driver_api as run_driver_api
 from .app import run_fleet_api as run_fleet_api
-from .app import run_server_app as run_server_app
 from .app import run_superlink as run_superlink
 from .app import start_server as start_server
 from .client_manager import ClientManager as ClientManager
 from .client_manager import SimpleClientManager as SimpleClientManager
+from .compat import start_driver as start_driver
 from .history import History as History
+from .run_serverapp import run_server_app as run_server_app
 from .server import Server as Server
 from .server_config import ServerConfig as ServerConfig
 from .serverapp import ServerApp as ServerApp
@@ -40,6 +41,7 @@
     "ServerApp",
     "ServerConfig",
     "SimpleClientManager",
+    "start_driver",
     "start_server",
     "strategy",
 ]

src/py/flwr/server/app.py

@@ -19,7 +19,7 @@
 import importlib.util
 import sys
 import threading
-from logging import DEBUG, ERROR, INFO, WARN
+from logging import ERROR, INFO, WARN
 from os.path import isfile
 from pathlib import Path
 from signal import SIGINT, SIGTERM, signal
@@ -47,7 +47,6 @@
 from .history import History
 from .server import Server
 from .server_config import ServerConfig
-from .serverapp import ServerApp, load_server_app
 from .strategy import FedAvg, Strategy
 from .superlink.driver.driver_servicer import DriverServicer
 from .superlink.fleet.grpc_bidi.grpc_server import (
@@ -65,72 +64,6 @@
 DATABASE = ":flwr-in-memory-state:"
 
 
-def run_server_app() -> None:
-    """Run Flower server app."""
-    event(EventType.RUN_SERVER_APP_ENTER)
-
-    args = _parse_args_run_server_app().parse_args()
-
-    # Obtain certificates
-    if args.insecure:
-        if args.root_certificates is not None:
-            sys.exit(
-                "Conflicting options: The '--insecure' flag disables HTTPS, "
-                "but '--root-certificates' was also specified. Please remove "
-                "the '--root-certificates' option when running in insecure mode, "
-                "or omit '--insecure' to use HTTPS."
-            )
-        log(
-            WARN,
-            "Option `--insecure` was set. "
-            "Starting insecure HTTP client connected to %s.",
-            args.server,
-        )
-        root_certificates = None
-    else:
-        # Load the certificates if provided, or load the system certificates
-        cert_path = args.root_certificates
-        if cert_path is None:
-            root_certificates = None
-        else:
-            root_certificates = Path(cert_path).read_bytes()
-        log(
-            DEBUG,
-            "Starting secure HTTPS client connected to %s "
-            "with the following certificates: %s.",
-            args.server,
-            cert_path,
-        )
-
-    log(
-        DEBUG,
-        "Flower will load ServerApp `%s`",
-        getattr(args, "server-app"),
-    )
-
-    log(
-        DEBUG,
-        "root_certificates: `%s`",
-        root_certificates,
-    )
-
-    log(WARN, "Not implemented: run_server_app")
-
-    server_app_dir = args.dir
-    if server_app_dir is not None:
-        sys.path.insert(0, server_app_dir)
-
-    def _load() -> ServerApp:
-        server_app: ServerApp = load_server_app(getattr(args, "server-app"))
-        return server_app
-
-    server_app = _load()
-
-    log(DEBUG, "server_app: `%s`", server_app)
-
-    event(EventType.RUN_SERVER_APP_LEAVE)
-
-
 def start_server(  # pylint: disable=too-many-arguments,too-many-locals
     *,
     server_address: str = ADDRESS_FLEET_API_GRPC_BIDI,
@@ -816,42 +749,3 @@ def _add_args_fleet_api(parser: argparse.ArgumentParser) -> None:
         type=int,
         default=1,
     )
-
-
-def _parse_args_run_server_app() -> argparse.ArgumentParser:
-    """Parse flower-server-app command line arguments."""
-    parser = argparse.ArgumentParser(
-        description="Start a Flower server app",
-    )
-
-    parser.add_argument(
-        "server-app",
-        help="For example: `server:app` or `project.package.module:wrapper.app`",
-    )
-    parser.add_argument(
-        "--insecure",
-        action="store_true",
-        help="Run the server app without HTTPS. By default, the app runs with "
-        "HTTPS enabled. Use this flag only if you understand the risks.",
-    )
-    parser.add_argument(
-        "--root-certificates",
-        metavar="ROOT_CERT",
-        type=str,
-        help="Specifies the path to the PEM-encoded root certificate file for "
-        "establishing secure HTTPS connections.",
-    )
-    parser.add_argument(
-        "--server",
-        default="0.0.0.0:9092",
-        help="Server address",
-    )
-    parser.add_argument(
-        "--dir",
-        default="",
-        help="Add specified directory to the PYTHONPATH and load Flower "
-        "app from there."
-        " Default: current working directory.",
-    )
-
-    return parser

src/py/flwr/server/compat/__init__.py

@@ -0,0 +1,22 @@
+# Copyright 2024 Flower Labs GmbH. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Flower ServerApp compatibility package."""
+
+
+from .app import start_driver as start_driver
+
+__all__ = [
+    "start_driver",
+]

src/py/flwr/server/driver/app.py → src/py/flwr/server/compat/app.py

@@ -33,8 +33,8 @@
 from flwr.server.server_config import ServerConfig
 from flwr.server.strategy import Strategy
 
+from ..driver.grpc_driver import GrpcDriver
 from .driver_client_proxy import DriverClientProxy
-from .grpc_driver import GrpcDriver
 
 DEFAULT_SERVER_ADDRESS_DRIVER = "[::]:9091"
 
@@ -111,10 +111,11 @@ def start_driver(  # pylint: disable=too-many-arguments, too-many-locals
     # Create the Driver
     if isinstance(root_certificates, str):
         root_certificates = Path(root_certificates).read_bytes()
-    driver = GrpcDriver(
+    grpc_driver = GrpcDriver(
         driver_service_address=address, root_certificates=root_certificates
     )
-    driver.connect()
+
+    grpc_driver.connect()
     lock = threading.Lock()
 
     # Initialize the Driver API server and config
@@ -134,7 +135,7 @@ def start_driver(  # pylint: disable=too-many-arguments, too-many-locals
     thread = threading.Thread(
         target=update_client_manager,
         args=(
-            driver,
+            grpc_driver,
             initialized_server.client_manager(),
             lock,
         ),
@@ -149,7 +150,7 @@ def start_driver(  # pylint: disable=too-many-arguments, too-many-locals
 
     # Stop the Driver API server and the thread
     with lock:
-        driver.disconnect()
+        grpc_driver.disconnect()
     thread.join()
 
     event(EventType.START_SERVER_LEAVE)

src/py/flwr/server/driver/app_test.py → src/py/flwr/server/compat/app_test.py

@@ -26,7 +26,8 @@
 )
 from flwr.proto.node_pb2 import Node  # pylint: disable=E0611
 from flwr.server.client_manager import SimpleClientManager
-from flwr.server.driver.app import update_client_manager
+
+from .app import update_client_manager
 
 
 class TestClientManagerWithDriver(unittest.TestCase):

src/py/flwr/server/driver/driver_client_proxy.py → src/py/flwr/server/compat/driver_client_proxy.py

@@ -31,7 +31,7 @@
 from flwr.proto import driver_pb2, node_pb2, task_pb2  # pylint: disable=E0611
 from flwr.server.client_proxy import ClientProxy
 
-from .grpc_driver import GrpcDriver
+from ..driver.grpc_driver import GrpcDriver
 
 SLEEP_TIME = 1
 

src/py/flwr/server/driver/driver_client_proxy_test.py → src/py/flwr/server/compat/driver_client_proxy_test.py

@@ -44,7 +44,8 @@
     Status,
 )
 from flwr.proto import driver_pb2, node_pb2, task_pb2  # pylint: disable=E0611
-from flwr.server.driver.driver_client_proxy import DriverClientProxy
+
+from .driver_client_proxy import DriverClientProxy
 
 MESSAGE_PARAMETERS = Parameters(tensors=[b"abc"], tensor_type="np")
 

src/py/flwr/server/driver/__init__.py

@@ -15,12 +15,10 @@
 """Flower driver SDK."""
 
 
-from .app import start_driver
 from .driver import Driver
 from .grpc_driver import GrpcDriver
 
 __all__ = [
     "Driver",
     "GrpcDriver",
-    "start_driver",
 ]