Cap fastapi <0.137 and fix execution API health empty-path route

airflow-core/pyproject.toml

@@ -95,7 +95,11 @@ dependencies = [
     "cryptography>=44.0.3",
     "deprecated>=1.2.13",
     "dill>=0.2.2",
-    "fastapi[standard-no-fastapi-cloud-cli]>=0.129.0",
+    # Cap below 0.137.0: FastAPI 0.137 switched to lazy router inclusion, which breaks cadwyn's
+    # versioned router generation (RouterGenerationError) and fails api-server / dag-processor
+    # startup. Relax once cadwyn supports FastAPI 0.137. See
+    # https://github.com/apache/airflow/issues/68562
+    "fastapi[standard-no-fastapi-cloud-cli]>=0.129.0,<0.137.0",
     "uvicorn>=0.37.0",
     "starlette>=1.0.1",
     "httpx>=0.25.0",

airflow-core/src/airflow/api_fastapi/execution_api/routes/__init__.py

@@ -38,7 +38,11 @@
 from airflow.api_fastapi.execution_api.security import require_auth
 
 execution_api_router = APIRouter()
-execution_api_router.include_router(health.router, prefix="/health", tags=["Health"])
+# health.router declares its full paths ("/health", "/health/ping") and is included without a
+# prefix, unlike the routers below. A root route registered as @router.get("") under an include-time
+# prefix=... raises "Prefix and path cannot be both empty" once FastAPI switched to lazy router
+# inclusion (>=0.137); see https://github.com/apache/airflow/issues/68562. Don't reintroduce a prefix here.
+execution_api_router.include_router(health.router, tags=["Health"])
 
 # _Every_ single endpoint under here must be authenticated. Some do further checks on top of these
 authenticated_router = VersionedAPIRouter(dependencies=[Security(require_auth)])  # type: ignore[list-item]

airflow-core/src/airflow/api_fastapi/execution_api/routes/health.py

@@ -25,12 +25,12 @@
 router = APIRouter()
 
 
-@router.get("")
+@router.get("/health")
 def health() -> dict:
     return {"status": "healthy"}
 
 
-@router.get("/ping")
+@router.get("/health/ping")
 async def ping(services=DepContainer):
     ok: list[str] = []
     failing: dict[str, str] = {}

airflow-core/tests/unit/api_fastapi/execution_api/routes/__init__.py

@@ -0,0 +1,16 @@
+# 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.

airflow-core/tests/unit/api_fastapi/execution_api/routes/test_health_routes.py

@@ -0,0 +1,38 @@
+# 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 fastapi.routing import APIRoute
+
+
+def test_health_router_avoids_empty_root_path():
+    """Regression guard for https://github.com/apache/airflow/issues/68562 (FastAPI >=0.137).
+
+    The break is specific: a root route registered with an empty path (``@router.get("")``) *and*
+    mounted under an include-time ``prefix=...`` raises ``FastAPIError: Prefix and path cannot be
+    both empty`` once FastAPI switched to lazy router inclusion. Older FastAPI merged the prefix in
+    eagerly and accepted it, so the version pin alone won't catch a reintroduction. The health
+    router therefore declares full, non-empty paths and is included without a prefix -- assert the
+    empty path stays gone, while leaving room for additional health sub-routes to be added later.
+    """
+    from airflow.api_fastapi.execution_api.routes import health
+
+    empty = [route.name for route in health.router.routes if isinstance(route, APIRoute) and not route.path]
+    assert not empty, f"Health routes must use explicit, non-empty paths (breaks FastAPI >=0.137): {empty}"
+
+    paths = {route.path for route in health.router.routes if isinstance(route, APIRoute)}
+    assert {"/health", "/health/ping"} <= paths