'Get current state of all Instances registered to an Load Balancer.
:type load_balancer_name: string
:param load_balancer_name: The name of the Load Balancer
:type instances: List of strings
:param instances: The instance ID\'s of the EC2 instances
to return status for.  If not provided,
the state of all instances will be returned.
:rtype: List of :class:`boto.ec2.elb.instancestate.InstanceState`
:return: list of state info for instances in this Load Balancer.'

def describe_instance_health(self, load_balancer_name, instances=None):

    params = {'LoadBalancerName': load_balancer_name}
    if instances:
        self.build_list_params(params, instances, 'Instances.member.%d.InstanceId')
    return self.get_list('DescribeInstanceHealth', params, [('member', InstanceState)])
