Add simple "Task API" server

[skip ci]

closes apache#43009

airflow/api_fastapi/app.py

@@ -44,20 +44,46 @@ def init_dag_bag(app: FastAPI) -> None:
     app.state.dag_bag = get_dag_bag()
 
 
-def create_app() -> FastAPI:
+def create_task_api_app(app: FastAPI) -> None:
+    """Create FastAPI app for task API."""
+    from airflow.api_fastapi.views.task_sdk import task_sdk_router
+
+    task_api_app = FastAPI(
+        title="Airflow Task API",
+        description="The private Airflow Task API.",
+        include_in_schema=False,
+    )
+
+    task_api_app.include_router(task_sdk_router)
+    app.mount("/task", task_api_app)
+
+
+def create_app(apps: list[str] | None = None) -> FastAPI:
     from airflow.configuration import conf
 
+    # TODO: Need to figure out how to get the 'apps' from the command line
+    # and pass it to the create_app function
+    # Passing it to the gunicorn command does not seem straightforward
+    # One possible option is to pass via environment variable (--env to gunicorn)
+    # https://docs.gunicorn.org/en/stable/settings.html#raw-env
+    apps_env = os.environ.get("AIRFLOW__API__APPS")
+    apps_list = apps_env.split(",") if apps_env else []
+    apps = apps or apps_list
+
     app = FastAPI(
+        title="Airflow API",
         description="Airflow API. All endpoints located under ``/public`` can be used safely, are stable and backward compatible. "
         "Endpoints located under ``/ui`` are dedicated to the UI and are subject to breaking change "
-        "depending on the need of the frontend. Users should not rely on those but use the public ones instead."
+        "depending on the need of the frontend. Users should not rely on those but use the public ones instead.",
     )
 
-    init_dag_bag(app)
-
-    init_views(app)
+    if not apps or "ui" in apps:
+        init_dag_bag(app)
+        init_views(app)
+        init_plugins(app)
 
-    init_plugins(app)
+    if not apps or "task-sdk" in apps:
+        create_task_api_app(app)
 
     allow_origins = conf.getlist("api", "access_control_allow_origins")
     allow_methods = conf.getlist("api", "access_control_allow_methods")

airflow/api_fastapi/openapi/v1-generated.yaml

@@ -1,6 +1,6 @@
 openapi: 3.1.0
 info:
-  title: FastAPI
+  title: Airflow API
   description: Airflow API. All endpoints located under ``/public`` can be used safely,
     are stable and backward compatible. Endpoints located under ``/ui`` are dedicated
     to the UI and are subject to breaking change depending on the need of the frontend.

airflow/api_fastapi/views/task_sdk/__init__.py

@@ -0,0 +1,23 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+from __future__ import annotations
+
+from airflow.api_fastapi.views.router import AirflowRouter
+from airflow.api_fastapi.views.task_sdk.health import health_router
+
+task_sdk_router = AirflowRouter()
+task_sdk_router.include_router(health_router)

airflow/api_fastapi/views/task_sdk/health.py

@@ -0,0 +1,27 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+
+from __future__ import annotations
+
+from airflow.api_fastapi.views.router import AirflowRouter
+
+health_router = AirflowRouter(tags=["Task SDK"])
+
+
+@health_router.get("/health")
+async def healthz() -> dict:
+    return {"status": "healthy"}

airflow/cli/cli_config.py

@@ -769,6 +769,9 @@ def string_lower_type(val):
     ("-L", "--access-logformat"),
     help="The access log format for gunicorn logs",
 )
+ARG_FASTAPI_API_APPS = Arg(
+    ("--apps",), help="Applications to run. Default is all", type=string_list_type, default=["ui", "task-sdk"]
+)
 
 
 # scheduler
@@ -1936,6 +1939,7 @@ class GroupCommand(NamedTuple):
             ARG_FASTAPI_API_ACCESS_LOGFILE,
             ARG_FASTAPI_API_ERROR_LOGFILE,
             ARG_FASTAPI_API_ACCESS_LOGFORMAT,
+            ARG_FASTAPI_API_APPS,
             ARG_LOG_FILE,
             ARG_SSL_CERT,
             ARG_SSL_KEY,

airflow/cli/commands/fastapi_api_command.py

@@ -57,6 +57,7 @@ def fastapi_api(args):
     """Start Airflow FastAPI API."""
     print(settings.HEADER)
 
+    apps = args.apps or []
     access_logfile = args.access_logfile or "-"
     error_logfile = args.error_logfile or "-"
     access_logformat = args.access_logformat
@@ -101,6 +102,8 @@ def fastapi_api(args):
         )
 
         pid_file, _, _, _ = setup_locations("fastapi-api", pid=args.pid)
+
+        # TODO: Need to pass "apps" to create_app somehow
         run_args = [
             sys.executable,
             "-m",
@@ -192,7 +195,7 @@ def start_and_monitor_gunicorn(args):
         if args.daemon:
             # This makes possible errors get reported before daemonization
             os.environ["SKIP_DAGS_PARSING"] = "True"
-            create_app()
+            create_app(apps)
             os.environ.pop("SKIP_DAGS_PARSING")
 
         pid_file_path = Path(pid_file)