Given the autoscale rule where the maximum instance limit is set to 5 and App1 uses 80% of available memory consistently over a 30-minute period, the scaling mechanism works as follows: Starting with 2 instances, after 15 minutes of average usage above 70%, the rule triggers adding an additional instance, resulting in 3 instances. After a 5-minute cooldown period, if the usage is still above 70%, another instance is added at the 20-minute mark, resulting in 4 instances. Another 5-minute cooldown at the 25-minute mark would add another instance, making it 5 instances. Thus, within the 30-minute duration, the maximum number of instances App1 can have is 5. Therefore, the correct answer is D.