# Copyright (c) 2016 Mirantis, 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.
import time
from kuryr_kubernetes import clients
from kuryr_kubernetes.handlers import health
from kuryr_kubernetes import utils
from oslo_config import cfg
from oslo_log import log as logging
LOG = logging.getLogger(__name__)
CONF = cfg.CONF
class Watcher(health.HealthHandler):
"""Observes K8s resources' events using K8s '?watch=true' API.
The `Watcher` maintains a list of K8s resources and manages the event
processing loops for those resources. Event handling is delegated to the
`callable` object passed as the `handler` initialization parameter that
will be run for each K8s event observed by the `Watcher`.
The `Watcher` can operate in two different modes based on the
`thread_group` initialization parameter:
- synchronous, when the event processing loops run on the same thread
that called 'add' or 'start' methods
- asynchronous, when each event processing loop runs on its own thread
(`oslo_service.threadgroup.Thread`) from the `thread_group`
When started, the `Watcher` will run the event processing loops for each
of the K8s resources on the list. Adding a K8s resource to the running
`Watcher` also ensures that the event processing loop for that resource is
running.
Stopping the `Watcher` or removing the specific K8s resource from the
list will request the corresponding running event processing loops to
stop gracefully, but will not interrupt any running `handler`. Forcibly
stopping any 'stuck' `handler` is not supported by the `Watcher` and
should be handled externally (e.g. by using `thread_group.stop(
graceful=False)` for asynchronous `Watcher`).
"""
def __init__(self, handler, thread_group=None, timeout=None):
"""Initializes a new Watcher instance.
:param handler: a `callable` object to be invoked for each observed
K8s event with the event body as a single argument.
Calling `handler` should never raise any exceptions
other than `eventlet.greenlet.GreenletExit` caused by
`eventlet.greenthread.GreenThread.kill` when the
`Watcher` is operating in asynchronous mode.
:param thread_group: an `oslo_service.threadgroup.ThreadGroup`
object used to run the event processing loops
asynchronously. If `thread_group` is not
specified, the `Watcher` will operate in a
synchronous mode.
"""
super(Watcher, self).__init__()
self._client = clients.get_kubernetes_client()
self._handler = handler
self._thread_group = thread_group
self._running = False
self._resources = set()
self._watching = {}
self._idle = {}
if timeout is None:
timeout = CONF.kubernetes.watch_retry_timeout
self._timeout = timeout
def add(self, path):
"""Adds ths K8s resource to the Watcher.
Adding a resource to a running `Watcher` also ensures that the event
processing loop for that resource is running. This method could block
for `Watcher`s operating in synchronous mode.
:param path: K8s resource URL path
"""
self._resources.add(path)
if self._running and path not in self._watching:
self._start_watch(path)
def remove(self, path):
"""Removes the K8s resource from the Watcher.
Also requests the corresponding event processing loop to stop if it
is running.
:param path: K8s resource URL path
"""
self._resources.discard(path)
if path in self._watching:
self._stop_watch(path)
def start(self):
"""Starts the Watcher.
Also ensures that the event processing loops are running. This method
could block for `Watcher`s operating in synchronous mode.
"""
self._running = True
for path in self._resources - set(self._watching):
self._start_watch(path)
def stop(self):
"""Stops the Watcher.
Also requests all running event processing loops to stop.
"""
self._running = False
for path in list(self._watching):
self._stop_watch(path)
def _start_watch(self, path):
tg = self._thread_group
self._idle[path] = True
if tg:
self._watching[path] = tg.add_thread(self._watch, path)
else:
self._watching[path] = None
self._watch(path)
def _stop_watch(self, path):
if self._idle.get(path):
if self._thread_group:
self._watching[path].stop()
def _graceful_watch_exit(self, path):
try:
self._watching.pop(path)
self._idle.pop(path)
LOG.info("Stopped watching '%s'", path)
except KeyError:
LOG.error("Failed to exit watch gracefully")
def _watch(self, path):
attempts = 0
deadline = 0
while self._running and path in self._resources:
try:
retry = False
if attempts == 1:
deadline = time.time() + self._timeout
if (attempts > 0 and
utils.exponential_sleep(deadline, attempts) == 0):
LOG.error("Failed watching '%s': deadline exceeded", path)
self._healthy = False
return
LOG.info("Started watching '%s'", path)
for event in self._client.watch(path):
# NOTE(esevan): Watcher retries watching for
# `self._timeout` duration with exponential backoff
# algorithm to tolerate against temporal exception such as
# temporal disconnection to the k8s api server.
attempts = 0
self._idle[path] = False
self._handler(event)
self._idle[path] = True
if not (self._running and path in self._resources):
return
except Exception as e:
LOG.warning("Restarting(%s) watching '%s': %s",
attempts, path, e)
attempts += 1
retry = True
finally:
if not retry:
self._graceful_watch_exit(path)