'Validate existing instances against this cluster\'s settings'

def validate_running_instances(self):

    cluster = self.cluster
    cluster.wait_for_active_spots()
    nodes = cluster.nodes
    if (not nodes):
        raise exception.ClusterValidationError('No    existing    nodes    found!')
    log.info('Validating    existing    instances...')
    mazone = cluster.master_node.placement
    cluster._zone = None
    if (cluster.zone and (cluster.zone.name != mazone)):
        raise exception.ClusterValidationError(("Running    cluster's    availability_zone    (%s)    !=    %s" % (mazone, cluster.zone.name)))
    for node in nodes:
        if (node.key_name != cluster.keyname):
            raise exception.ClusterValidationError(("%s's    key_name    (%s)    !=    %s" % (node.alias, node.key_name, cluster.keyname)))
