def get_planner_instance(env):
    global planner_instance
    if not planner_instance:
        fqcn = env.get_property(DEFAULT_CONFIG_FILE, PROPERTY_PLANNER_CLASS, DEFAULT_PLANNER_CLASS)
        env.log("Creating a new planner instance of {}".format(fqcn))
        klass = find_class(fqcn)
        planner_instance = klass(env)
    return planner_instance