Simple master election using RethinkDB and gevent

master.py

#!/usr/bin/env python
import rethinkdb as r
import gevent
import gevent.monkey

gevent.monkey.patch_all()

LOCK_TIMEOUT = 15
UPDATE_TIMEOUT = 5

r.connect().repl()

r.branch(r.table_list().contains('locks'),
         r.expr({"created": 1}),
         r.table_create('locks')).run()


class MasterElectionExample:

    def __init__(self):
        self.is_master = False
        self.request_master_election()

        while True:
            if self.is_master:
                print 'i am the master, updating lock'
                self.update_lock('master')
            else:
                self.request_master_election()
            gevent.sleep(UPDATE_TIMEOUT)

    def aquire_lock(self, lock_name):
        res = r.branch(r.table('locks').get(lock_name),
                       r.do(r.table('locks').get(lock_name),
                            lambda lock: r.branch(
                                lock['time'] > (r.now() - LOCK_TIMEOUT),
                                r.expr(
                                    {"unchanged": 1, "replaced": 0, "inserted": 0}),
                                r.table('locks').replace(
                                    {"id": lock_name, "time": r.now()})
                            )
                            ),
                       r.table('locks').insert(
                           {"id": lock_name, "time": r.now()})
                       ).run()
        print res
        return res['inserted'] == 1 or res['replaced'] == 1

    def update_lock(self, lock_name):
        r.table('locks').update({'id': lock_name, 'time': r.now()}).run()

    def request_master_election(self):
        if self.aquire_lock('master'):
            self.is_master = True
            print 'i am the master. :)'
        else:
            self.is_master = False
            print 'i am not the master. :('

master = MasterElectionExample()