Add asyncio eventloop.

This commits introduces the asyncio event loop as well as the base
abstract class to define watchers.

It is in a very simple approach (it does not reschedule watchers if
they fail) but it lets you to see the proposal of hierarchy in watchers
as well as the methods that a watcher has to implement (see the pod
module).

Partial-Implements: blueprint kuryr-k8s-integration
Co-Authored-By: Taku Fukushima <f.tac.mac@gmail.com>
Co-Authored-By: Antoni Segura Puimedon
Change-Id: I91975dd197213c1a6b0e171c1ae218a547722eeb

kuryr_kubernetes/server.py

@@ -10,34 +10,51 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import asyncio
 import sys
-import time
 
 from kuryr.lib._i18n import _LI
 from oslo_log import log as logging
 from oslo_service import service
 
 from kuryr_kubernetes import config
+from kuryr_kubernetes.watchers import pod
 
 
 LOG = logging.getLogger(__name__)
 
 
 class KuryrK8sService(service.Service):
+    """Kuryr-Kubernetes base service.
+
+    This class extends the oslo_service.service.Service class to provide an
+    asynchronous event loop. It assumes that all the elements of the
+    `_watchers` list has a method called `watch` (normally, implemented by the
+    class `kuryr_kubernetes.watchers.base.AbstractBaseWatcher`).
+
+    The event loop is the default used by asyncio (asyncio.SelectorEventLoop)
+    """
 
     def __init__(self):
         super(KuryrK8sService, self).__init__()
+        self._event_loop = asyncio.new_event_loop()
+        self._watchers = [
+            pod.PodWatcher
+        ]
 
     def start(self):
-        # TODO(devvesa): Remove this line as soon as it does anything
-        LOG.info(_LI("I am doing nothing"))
+        LOG.info(_LI("Service '%(class_name)s' started"),
+                 {'class_name': self.__class__.__name__})
+
+        for watcher in self._watchers:
+            instance = watcher(self._event_loop)
+            self._event_loop.create_task(instance.watch())
         try:
-            while(True):
-                time.sleep(5)
-                # TODO(devvesa): Remove this line as soon as does anything
-                LOG.info(_LI("Keep doing nothing"))
-        finally:
+            self._event_loop.run_forever()
+            self._event_loop.close()
+        except Exception:
             sys.exit(1)
+        sys.exit(0)
 
     def wait(self):
         """Waits for K8sController to complete."""

kuryr_kubernetes/utils.py

@@ -0,0 +1,22 @@
+# 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.
+
+from oslo_serialization import jsonutils
+
+
+def utf8_json_decoder(byte_data):
+    """Deserializes the bytes into UTF-8 encoded JSON.
+
+    :param byte_data: The bytes to be converted into the UTF-8 encoded JSON.
+    :returns: The UTF-8 encoded JSON represented by Python dictionary format.
+    """
+    return jsonutils.loads(byte_data.decode('utf8'))

kuryr_kubernetes/watchers/base.py

@@ -0,0 +1,123 @@
+# 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 abc
+import requests
+
+from kuryr.lib._i18n import _LE
+from oslo_log import log as logging
+
+from kuryr_kubernetes.aio import headers as aio_headers
+from kuryr_kubernetes.aio import methods as aio_methods
+from kuryr_kubernetes import config
+from kuryr_kubernetes import utils
+
+LOG = logging.getLogger(__name__)
+
+ADDED_EVENT = 'ADDED'
+DELETED_EVENT = 'DELETED'
+MODIFIED_EVENT = 'MODIFIED'
+
+
+class AbstractBaseWatcher(object):
+    """Base abstract watcher.
+
+    This class implements the default interface for the KuryrK8sService task
+    scheduler, which is the `watch` (no parameters) interface.
+
+    It also define a serie of abstract methods that actual watchers have to
+    implement in order to deal directly with events without worrying about
+    connection and serialization details.
+
+    These methods are:
+
+        * get_endpoint(self): return a resource URL exposed on Kubernetes API
+                              as a string (such as "/api/v1/pods")
+        * on_add/on_modify/on_delete: actions to do according to each event
+                                      type.
+
+    These methods have to follow the async/await python3.5 syntax
+    """
+
+    def __init__(self, event_loop):
+        self._event_loop = event_loop
+
+    @abc.abstractmethod
+    def get_api_endpoint(self):
+        pass
+
+    @property
+    def api_endpoint(self):
+        k8s_root = config.CONF.kubernetes.api_root
+        return k8s_root + self.get_api_endpoint() + "?watch=true"
+
+    async def _on_event(self, event): # flake8: noqa
+
+        event_type = event['type']
+        if event_type == ADDED_EVENT:
+            await self.on_add(event)
+        elif event_type == DELETED_EVENT:
+            await self.on_delete(event)
+        elif event_type == MODIFIED_EVENT:
+            await self.on_modify(event)
+        else:
+            LOG.warning(_LW("Unhandled event type '%(event_type)s'"),
+                        {'event_type': event})
+
+    @abc.abstractmethod
+    async def on_add(self, event):
+        pass
+
+    @abc.abstractmethod
+    async def on_modify(self, event):
+        pass
+
+    @abc.abstractmethod
+    async def on_delete(self, event):
+        pass
+
+    async def watch(self):
+        """Watches the endpoint and calls the callback with its response.
+
+        This is an endless task that keeps the event loop running forever
+        """
+        response = await self._get_chunked_response()
+        while True:
+            content = await response.read_line()
+            LOG.debug('Received new event from %(watcher)s:\n\n\t'
+                      '%(event)s.\n\n',
+                      {'watcher': self.__class__.__name__,
+                       'event': str(content)})
+            await self._on_event(content)
+
+    async def _get_chunked_response(self):
+        """Get the response from Kubernetes API."""
+        response = await aio_methods.get(
+            endpoint=self.api_endpoint,
+            loop=self._event_loop,
+            decoder=utils.utf8_json_decoder)
+
+        status, reason, hdrs = await response.read_headers()
+        if status != requests.codes.ok:  # Function returns 200
+            LOG.error(_LE('GET request to endpoint %(ep)s failed with '
+                          'status %(status)s and reason %(reason)s'),
+                      {'ep': endpoint, 'status': status, 'reason': reason})
+            raise requests.exceptions.HTTPError('{}: {}. Endpoint {}'.format(
+                status, reason, endpoint))
+        if hdrs.get(aio_headers.TRANSFER_ENCODING) != 'chunked':
+            LOG.error(_LE('watcher GET request to endpoint %(ep)s is not '
+                          'chunked. headers: %(hdrs)s'),
+                      {'ep': endpoint, 'hdrs': hdrs})
+            raise IOError(_('Can only watch endpoints that returned chunked '
+                            'encoded transfers'))
+
+        return response

kuryr_kubernetes/watchers/pod.py

@@ -0,0 +1,38 @@
+# 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.
+
+from kuryr.lib._i18n import _LI
+from oslo_log import log as logging
+
+from kuryr_kubernetes.watchers import base
+
+LOG = logging.getLogger(__name__)
+
+
+class PodWatcher(base.AbstractBaseWatcher):
+
+    ENDPOINT = "/api/v1/pods"
+
+    def __init__(self, event_loop):
+        super().__init__(event_loop)
+
+    def get_api_endpoint(self):
+        return self.ENDPOINT
+
+    async def on_add(self, event): # flake8: noqa
+        LOG.info(_LI('Received an ADDED event on a Pod'))
+
+    async def on_modify(self, event):
+        LOG.info(_LI('Received a MODIFIED event on a Pod'))
+
+    async def on_delete(self, event):
+        LOG.info(_LI('Received a DELETED event on a Pod'))