1. A method in a computer system for guaranteeing execution of a content image, the method comprising: under the control of an update client executing on the computer system, obtaining the content image and its associated content image policy for execution of the content image on the computer system, the content image policy specifying attributes specific to the content image including an approximate execution time for the content image and an indication whether to obey or not obey a service window policy of the computer system; when the content image policy indicates to obey a service window policy, determining whether a service window is available for executing the content image, a service window is available when a present time is at least a start time of the service window and time from the present time to an end time of the service window is at least the approximate execution time for the content image; and upon determining that the service window is available, executing the content image on the computer system; and when the content image policy indicates to not obey a service window policy, executing the content image on the computer system without regard to any service window policy.