Find the private IP and ENI of an instance that's pointed to in a route.

    Returns (ipaddr, eni) tuple.

def get_instance_private_ip_from_route(instance, route):
    """
    Find the private IP and ENI of an instance that's pointed to in a route.

    Returns (ipaddr, eni) tuple.

    """
    ipaddr = None
    for eni in instance.interfaces:
        if eni.id == route.interface_id:
            ipaddr = eni.private_ip_address
            break
    return ipaddr, eni if ipaddr else None