zuul/zk.py

#!/usr/bin/env python
#
# 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 json
import logging
import time
from kazoo.client import KazooClient, KazooState
from kazoo import exceptions as kze
from kazoo.recipe.lock import Lock

# States:
# We are building this node but it is not ready for use.
BUILDING = 'building'
# The node is ready for use.
READY = 'ready'
# The node should be deleted.
DELETING = 'deleting'

STATES = set([BUILDING, READY, DELETING])


class LockException(Exception):
    pass


class ZooKeeper(object):
    '''
    Class implementing the ZooKeeper interface.

    This class uses the facade design pattern to keep common interaction
    with the ZooKeeper API simple and consistent for the caller, and
    limits coupling between objects. It allows for more complex interactions
    by providing direct access to the client connection when needed (though
    that is discouraged). It also provides for a convenient entry point for
    testing only ZooKeeper interactions.
    '''

    log = logging.getLogger("zuul.zk.ZooKeeper")

    REQUEST_ROOT = '/nodepool/requests'
    NODE_ROOT = '/nodepool/nodes'

    def __init__(self):
        '''
        Initialize the ZooKeeper object.
        '''
        self.client = None
        self._became_lost = False

    def _dictToStr(self, data):
        return json.dumps(data)

    def _strToDict(self, data):
        return json.loads(data)

    def _connection_listener(self, state):
        '''
        Listener method for Kazoo connection state changes.

        .. warning:: This method must not block.
        '''
        if state == KazooState.LOST:
            self.log.debug("ZooKeeper connection: LOST")
            self._became_lost = True
        elif state == KazooState.SUSPENDED:
            self.log.debug("ZooKeeper connection: SUSPENDED")
        else:
            self.log.debug("ZooKeeper connection: CONNECTED")

    @property
    def connected(self):
        return self.client.state == KazooState.CONNECTED

    @property
    def suspended(self):
        return self.client.state == KazooState.SUSPENDED

    @property
    def lost(self):
        return self.client.state == KazooState.LOST

    @property
    def didLoseConnection(self):
        return self._became_lost

    def resetLostFlag(self):
        self._became_lost = False

    def connect(self, hosts, read_only=False):
        '''
        Establish a connection with ZooKeeper cluster.

        Convenience method if a pre-existing ZooKeeper connection is not
        supplied to the ZooKeeper object at instantiation time.

        :param str hosts: Comma-separated list of hosts to connect to (e.g.
            127.0.0.1:2181,127.0.0.1:2182,[::1]:2183).
        :param bool read_only: If True, establishes a read-only connection.

        '''
        if self.client is None:
            self.client = KazooClient(hosts=hosts, read_only=read_only)
            self.client.add_listener(self._connection_listener)
            self.client.start()

    def disconnect(self):
        '''
        Close the ZooKeeper cluster connection.

        You should call this method if you used connect() to establish a
        cluster connection.
        '''
        if self.client is not None and self.client.connected:
            self.client.stop()
            self.client.close()
            self.client = None

    def resetHosts(self, hosts):
        '''
        Reset the ZooKeeper cluster connection host list.

        :param str hosts: Comma-separated list of hosts to connect to (e.g.
            127.0.0.1:2181,127.0.0.1:2182,[::1]:2183).
        '''
        if self.client is not None:
            self.client.set_hosts(hosts=hosts)

    def submitNodeRequest(self, node_request, watcher):
        '''
        Submit a request for nodes to Nodepool.

        :param NodeRequest node_request: A NodeRequest with the
            contents of the request.

        :param callable watcher: A callable object that will be
            invoked each time the request is updated.  It is called
            with two arguments: (node_request, deleted) where
            node_request is the same argument passed to this method,
            and deleted is a boolean which is True if the node no
            longer exists (notably, this will happen on disconnection
            from ZooKeeper).  The watcher should return False when
            further updates are no longer necessary.
        '''
        priority = 100  # TODO(jeblair): integrate into nodereq

        data = node_request.toDict()
        data['created_time'] = time.time()

        path = '%s/%s-' % (self.REQUEST_ROOT, priority)
        path = self.client.create(path, self._dictToStr(data),
                                  makepath=True,
                                  sequence=True, ephemeral=True)
        reqid = path.split("/")[-1]
        node_request.id = reqid

        def callback(data, stat):
            if data:
                data = self._strToDict(data)
                node_request.updateFromDict(data)
                request_nodes = node_request.nodeset.getNodes()
                for i, nodeid in enumerate(data.get('nodes', [])):
                    node_path = '%s/%s' % (self.NODE_ROOT, nodeid)
                    node_data, node_stat = self.client.get(node_path)
                    node_data = self._strToDict(node_data)
                    request_nodes[i].id = nodeid
                    request_nodes[i].updateFromDict(node_data)
            deleted = (data is None)  # data *are* none
            return watcher(node_request, deleted)

        self.client.DataWatch(path, callback)

    def deleteNodeRequest(self, node_request):
        '''
        Delete a request for nodes.

        :param NodeRequest node_request: A NodeRequest with the
            contents of the request.
        '''

        path = '%s/%s' % (self.REQUEST_ROOT, node_request.id)
        try:
            self.client.delete(path)
        except kze.NoNodeError:
            pass

    def storeNode(self, node):
        '''Store the node.

        The node is expected to already exist and is updated in its
        entirety.

        :param Node node: The node to update.
        '''

        path = '%s/%s' % (self.NODE_ROOT, node.id)
        self.client.set(path, self._dictToStr(node.toDict()))

    def lockNode(self, node, blocking=True, timeout=None):
        '''
        Lock a node.

        This should be called as soon as a request is fulfilled and
        the lock held for as long as the node is in-use.  It can be
        used by nodepool to detect if Zuul has gone offline and the
        node should be reclaimed.

        :param Node node: The node which should be locked.
        '''

        lock_path = '%s/%s/lock' % (self.NODE_ROOT, node.id)
        try:
            lock = Lock(self.client, lock_path)
            have_lock = lock.acquire(blocking, timeout)
        except kze.LockTimeout:
            raise LockException(
                "Timeout trying to acquire lock %s" % lock_path)

        # If we aren't blocking, it's possible we didn't get the lock
        # because someone else has it.
        if not have_lock:
            raise LockException("Did not get lock on %s" % lock_path)

        node.lock = lock

    def unlockNode(self, node):
        '''
        Unlock a node.

        The node must already have been locked.

        :param Node node: The node which should be unlocked.
        '''

        if node.lock is None:
            raise LockException("Node %s does not hold a lock" % (node,))
        node.lock.release()
        node.lock = None