hypervisor_factory.py

from docker_driver import DockerDriver
from libvirt_driver import Libvirt


##
# 
#     A singletone class for creating hypervisor driver objects. For an
#     instantiation of nf.io there can be exactly one object of only one type of
#     hyperviosr. HyervisorFactory takes care of the creation logic.
#     
class HypervisorFactory(object):

    __hyp_instance = None
    __hyp_instance_type = None

    ##
    # 
    #         Instantiates a HypervisorFactory object.
    # 
    #         Args:
    #             hypervisor_type: The type of hypervisor object to instantiate. Valid
    #                 hypervisor types are 'DockerDriver' and 'Libvirt' for the time being.
    # 
    #         Returns:
    #             Nothing. Initializaes the factory object.
    # 
    #         Note:
    #             If this factory class is instantiated multiple times with different
    #             types of hypervisor_type argument then it raises a ValueError.
    # 
    #             If this factory class is instantiated with a hypervisor type other
    #             than Docker or Libvirt it raises a TypeError.
    #         
    def __init__(self, hypervisor_type="DockerDriver"):
        if not HypervisorFactory.__hyp_instance:
            if hypervisor_type == "DockerDriver":
                HypervisorFactory.__hyp_instance_type = hypervisor_type
                HypervisorFactory.__hyp_instance = DockerDriver()
            elif hypervisor_type == "Libvirt":
                HypervisorFactory.__hyp_instance_type = hypervisor_type
                HypervisorFactory.__hyp_instance = Libvirt()
            else:
                raise TypeError(
                    "Invalid hypervisor type. Valid types are: Docker, Libvirt")
        elif HypervisorFactory.__hyp_instance_type != hypervisor_type:
            raise ValueError(
                "An instantiation of type " +
                HypervisorFactory.__hyp_instance_type +
                " already exists.")

    @staticmethod
    ##
    # 
    #         Returns the hypervisor driver nstance. If the instance is not initialized then
    #         a RuntimeError is raised.
    #         
    def get_hypervisor_instance():
        if HypervisorFactory.__hyp_instance is not None:
            return HypervisorFactory.__hyp_instance
        else:
            raise RuntimeError("Hypervisor not initialized.")