def find_existing(self):
        """
        Finds existing rule in secgroup.

        Populates ``self.create_these_rules`` and ``self.delete_these_rules``.

        """
        sg = self.consul.find_secgroup(self.name)

        current = sg.rules
        log.debug('Current rules: %s' % current)
        log.debug('Intended rules: %s' % self.rules)
        exp_rules = []
        for rule in self.rules:
            exp = (
                    rule[A.secgroup.PROTOCOL],
                    rule[A.secgroup.FROM],
                    rule[A.secgroup.TO],
                    rule[A.secgroup.SOURCE],
                    )
            exp_rules.append(exp)
            if exp in current:
                del current[exp]
            else:
                self.create_these_rules.append(exp)

        self.delete_these_rules.extend(current.itervalues())

        log.debug('Create these rules: %s' % self.create_these_rules)
        log.debug('Delete these rules: %s' % self.delete_these_rules)
Finds existing rule in secgroup.

        Populates ``self.create_these_rules`` and ``self.delete_these_rules``.