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# 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
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from __future__ import annotations

import logging
from http.server import BaseHTTPRequestHandler, HTTPServer

from sqlalchemy import select

from airflow.configuration import conf
from airflow.jobs.job import Job
from airflow.jobs.scheduler_job_runner import SchedulerJobRunner
from airflow.utils.net import get_hostname
from airflow.utils.session import create_session

log = logging.getLogger(__name__)


class HealthServer(BaseHTTPRequestHandler):
    """Small webserver to serve scheduler health check."""

    def do_GET(self):
        if self.path == "/health":
            try:
                with create_session() as session:
                    scheduler_job = session.scalar(
                        select(Job)
                        .filter_by(job_type=SchedulerJobRunner.job_type)
                        .filter_by(hostname=get_hostname())
                        .order_by(Job.latest_heartbeat.desc())
                        .limit(1)
                    )
                if scheduler_job and scheduler_job.is_alive():
                    self.send_response(200)
                    self.end_headers()
                else:
                    self.send_error(503)
            except Exception:
                log.exception("Exception when executing Health check")
                self.send_error(503)
        else:
            self.send_error(404)


def serve_health_check():
    """Start a http server to serve scheduler health check."""
    health_check_host = conf.get("scheduler", "SCHEDULER_HEALTH_CHECK_SERVER_HOST")
    health_check_port = conf.getint("scheduler", "SCHEDULER_HEALTH_CHECK_SERVER_PORT")
    httpd = HTTPServer((health_check_host, health_check_port), HealthServer)
    httpd.serve_forever()


if __name__ == "__main__":
    serve_health_check()
