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node.py
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node.py
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"""
The actual implementation of raft.
"""
import math
from message import AppendEntries, AppendEntriesResponse, RequestVote, RequestVoteResponse
class DownNode:
"""
DownNode is a mock node, intended to interoperate with the powerbroker to
represent a node that is powered down.
It's methods simply pass
"""
def receive(self, sender, message):
"Downed nodes receive no messages"
pass
def timer_trip(self):
"Downed Nodes have no timers"
pass
# pylint: disable=too-many-instance-attributes
class Node:
"""
The workhorse of this raft implementation.
"""
def __init__(self, node_id, conf, rng, broker):
self.node_id = node_id
self.conf = conf
self.rng = rng
self.broker = broker
self.term = 0
self.log = [] # list[tuple(term, entry)]
self.commit_index = 0
self.last_applied = 0
self.voted_for = None
self.node_type = 'Follower'
self.votes_received = set()
self.election_timeout = self.calculate_election_timeout()
def test_log(self, event):
"This logs events for debugging purposes"
assert 'event_type' in event
event['originating_node'] = self.node_id
event['current_term'] = self.term
event['current_type'] = self.node_type
self.broker.log(event)
def calculate_election_timeout(self):
" TODO "
return self.rng.randint(self.conf['election_timeout_window'][0],
self.conf['election_timeout_window'][1])
def is_candidate(self):
"TODO"
return self.node_type == 'Candidate'
def is_follower(self):
"TODO"
return self.node_type == 'Follower'
def is_leader(self):
"TODO"
return self.node_type == 'Leader'
def setup(self):
"Emulates a node booting up"
self.broker.set_timeout(self.node_id, self.election_timeout)
def change_type(self, new_type):
"""
Convert this node to a different type, and make any other needed state changes.
"""
self.test_log({'event_type':'change_type', 'to':new_type})
#-TODO always log instead of logging when different?
if self.node_type != new_type:
self.test_log({'to_type': new_type,
'event_type': 'change_type'})
assert new_type == 'Follower' or new_type == 'Candidate' or new_type == 'Leader'
if new_type == 'Leader':
assert self.node_type != 'Follower'
self.node_type = new_type
if new_type == 'Follower' or new_type == 'Candidate':
self.broker.set_timeout(self.node_id, self.election_timeout)
elif new_type == 'Leader':
self.broker.set_timeout(
self.node_id, self.conf['heartbeat_timeout'])
def update_term(self, term, new_candidate):
"""
If term is greater than the current term, update the term and make any
other needed state changes.
We avoid resetting the node to 'Follower' if we're updating the term
because the node is starting a new election.
"""
self.test_log({'event_type':'update_term', 'new_term':term, 'new_candidate':new_candidate})
if term > self.term:
if not new_candidate:
self.change_type('Follower')
self.term = term
self.votes_received = set()
self.voted_for = None
self.election_timeout = self.calculate_election_timeout()
self.test_log({'event_type': 'update_term'})
def receive(self, sender, message):
"TODO"
self.update_term(message.term, False)
assert isinstance(message, (AppendEntries, RequestVote, AppendEntriesResponse,\
RequestVoteResponse))
if isinstance(message, AppendEntries):
if self.is_follower():
self.broker.set_timeout(self.node_id, self.election_timeout)
elif self.is_candidate() or self.is_leader():
self.change_type('Follower')
else:
# This case will fire when we add cluster config changes.
assert False
elif isinstance(message, RequestVote):
if message.term < self.term or self.voted_for is not None:
self.broker.send_to(self.node_id, sender,
RequestVoteResponse(self.term, False))
else:
self.broker.send_to(self.node_id, sender,
RequestVoteResponse(self.term, True))
self.voted_for = sender
self.test_log({'event_type': 'cast_vote', 'voted_for': sender})
elif isinstance(message, AppendEntriesResponse):
pass
elif isinstance(message, RequestVoteResponse):
if message.vote_granted and self.is_candidate():
self.votes_received.add(sender)
if len(self.votes_received) > math.floor(len(self.conf['nodes']) / 2):
self.change_type('Leader')
def timer_trip(self):
"TODO"
#-TODO: this if statement was added to fix a "compile error". This was not
# thought through and may be wrong.
last_logged_term = -1
last_logged_entry = None
if self.log:
last_logged_term = self.log[-1][0]
last_logged_entry = self.log[-1][1]
if not self.is_leader():
self.change_type('Candidate')
self.update_term(self.term + 1, True)
self.votes_received.add(self.node_id)
self.voted_for = self.node_id
self.test_log({"event_type": "cast_vote", "voted_for": self.node_id})
for node in self.conf['nodes']:
if self.node_id != node:
self.broker.send_to(self.node_id, node,
RequestVote(self.term, self.node_id,
len(self.log), last_logged_term))
else:
for node in self.conf['nodes']:
if self.node_id != node:
self.broker.send_to(self.node_id, node,
AppendEntries(self.term, self.node_id,
len(self.log), last_logged_entry,
[], self.commit_index))
self.broker.set_timeout(
self.node_id, self.conf['heartbeat_timeout'])