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94 lines
4.0 KiB
Python
94 lines
4.0 KiB
Python
import logging
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from helpers.dcs import DCSError
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from psycopg2 import InterfaceError, OperationalError
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logger = logging.getLogger(__name__)
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class Ha:
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def __init__(self, state_handler, etcd):
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self.state_handler = state_handler
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self.dcs = etcd
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self.cluster = None
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def load_cluster_from_dcs(self):
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self.cluster = self.dcs.get_cluster()
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def acquire_lock(self):
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return self.dcs.attempt_to_acquire_leader()
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def update_lock(self):
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return self.dcs.update_leader(self.state_handler)
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def has_lock(self):
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lock_owner = self.cluster.leader and self.cluster.leader.name
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logger.info('Lock owner: %s; I am %s', lock_owner, self.state_handler.name)
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return lock_owner == self.state_handler.name
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def demote(self):
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return self.state_handler.demote(self.cluster.leader)
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def follow_the_leader(self):
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return self.state_handler.follow_the_leader(self.cluster.leader)
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def run_cycle(self):
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try:
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self.load_cluster_from_dcs()
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if not self.state_handler.is_healthy():
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has_lock = self.has_lock()
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self.state_handler.write_recovery_conf(None if has_lock else self.cluster.leader)
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self.state_handler.start()
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if not has_lock:
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return 'started as a secondary'
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logger.info('started as readonly because i had the session lock')
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self.load_cluster_from_dcs()
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if self.cluster.is_unlocked():
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if self.state_handler.is_healthiest_node(self.cluster):
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if self.acquire_lock():
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if self.state_handler.is_leader() or self.state_handler.is_promoted:
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return 'acquired session lock as a leader'
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else:
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self.state_handler.promote()
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return 'promoted self to leader by acquiring session lock'
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else:
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self.load_cluster_from_dcs()
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if self.state_handler.is_leader():
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self.demote()
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return 'demoted self due after trying and failing to obtain lock'
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else:
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self.follow_the_leader()
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return 'following new leader after trying and failing to obtain lock'
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else:
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self.load_cluster_from_dcs()
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if self.state_handler.is_leader():
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self.demote()
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return 'demoting self because i am not the healthiest node'
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else:
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self.follow_the_leader()
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return 'following a different leader because i am not the healthiest node'
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else:
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if self.has_lock() and self.update_lock():
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if self.state_handler.is_leader() or self.state_handler.is_promoted:
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return 'no action. i am the leader with the lock'
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else:
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self.state_handler.promote()
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return 'promoted self to leader because i had the session lock'
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else:
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logger.info('does not have lock')
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if self.state_handler.is_leader():
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self.demote()
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return 'demoting self because i do not have the lock and i was a leader'
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else:
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self.follow_the_leader()
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return 'no action. i am a secondary and i am following a leader'
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except DCSError:
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logger.error('Error communicating with DCS')
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if self.state_handler.is_leader():
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self.state_handler.demote(None)
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return 'demoted self because DCS is not accessible and i was a leader'
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except (InterfaceError, OperationalError):
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logger.error('Error communicating with Postgresql. Will try again')
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