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#!/usr/bin/env python
# Copyright 2016 Google Inc. 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.
"""Example of using the Compute Engine API to watch for maintenance notices.
For more information, see the README.md under /compute.
"""
# [START all]
import time
import requests
METADATA_URL = 'http://metadata.google.internal/computeMetadata/v1/'
METADATA_HEADERS = {'Metadata-Flavor': 'Google'}
def wait_for_maintenance(callback):
url = METADATA_URL + 'instance/maintenance-event'
last_maintenance_event = None
# [START hanging_get]
last_etag = '0'
while True:
r = requests.get(
url,
params={'last_etag': last_etag, 'wait_for_change': True},
headers=METADATA_HEADERS)
# During maintenance the service can return a 503, so these should
# be retried.
if r.status_code == 503:
time.sleep(1)
continue
r.raise_for_status()
last_etag = r.headers['etag']
# [END hanging_get]
if r.text == 'NONE':
maintenance_event = None
else:
# Possible events:
# MIGRATE_ON_HOST_MAINTENANCE: instance will be migrated
# SHUTDOWN_ON_HOST_MAINTENANCE: instance will be shut down
maintenance_event = r.text
if maintenance_event != last_maintenance_event:
last_maintenance_event = maintenance_event
callback(maintenance_event)
def maintenance_callback(event):
if event:
print('Undergoing host maintenance: {}'.format(event))
else:
print('Finished host maintenance')
def main():
wait_for_maintenance(maintenance_callback)
if __name__ == '__main__':
main()
# [END all]