1. A method, comprising: identifying service impact events in an alarm dataset from a cloud software defined network, the service impact events including service alarms; identifying alarm sources associated with the service impact events; identifying impacted network service alarms provided in the cloud software defined network, the impacted network service alarms being identified according to the alarm sources; identifying service alarm type classifications for the impacted network service alarms; by a processor of a service impact event analyzer, identifying a service impact model comprising the service alarm type classifications and the service impact events, the model describing impacts of the service impact events on network services; using the service impact model, identifying association rules of parent and child event relationships of a particular service impact event of the service impact events, so that a parent event is determined to be a primary event for root causes of trouble, and child events are determined to be correlated to the parent event, the parent event comprising a parent event time interval beginning at a parent event onset time and ending at a parent event clear time later than the parent event onset time, each child event comprising a child event time interval beginning at a child event onset time and ending at a child event clear time later than the child event onset time, wherein each child event is determined to be correlated to the parent event only if the child event is generated due to the parent event and the child event onset time is within the parent event time interval; by the processor, computing a time duration of the particular service impact event by subtracting the parent event onset time from a particular child event clear time of the child events determined to be correlated to the parent event of the particular service impact event; and by the processor, evaluating a risk area and degree of service assurance based on the time duration and on the service alarm type classifications.