- [Morgan] All right, first sample question for this domain. As usual, we will read through the stem, and identify any critical pieces to pay close attention to. Then, we will explore all of the responses, and discuss which response is the key, and which are the distractors. All right, now for the stem. A company has an application that only needs to run for 2 hours at any time during the day. Which Amazon EC2 instance type will be the most cost-effective for this application? Taking a closer look at the stem. What is it really asking for? Well, you know you have an application that needs to run for only 2 hours at a time. So, a timeframe is provided for the runtime of the application, which could be important. Then, it's asking for the Amazon EC2 instance type that is the most cost-effective. The really important thing here is the words, most cost-effective. This lets you know, you should be answering this question with costs top of mind. Now, time for the responses. A, Dedicated Instances. B, On-Demand Instances. C, Reserved Instances. Or D, Spot Instances. Now, we will give you 3 seconds to determine the answer. If you need more time than that, please pause now. Three, two, one. All right, time's up. Let's discuss the responses. The key to this stem is D, Spot Instances. So, why is this the correct answer? Well, the question pointed out that the application only needs to be run for 2 hours at a time. And if you have worked with, or studied, Amazon EC2 Spot Instances, you know that they should not really be used for long-running applications, but they can be used for shorter-running applications that can be interrupted. Since the application only needs to run for 2 hours, that is the first clue that Spot could be the key. The other thing here, is that the stem is looking for the most cost-effective solution. Spot Instances enable you to take a steep discount from the On-Demand price for Amazon EC2 instances, up to 90 percent off of the On-Demand price. So, if the workload is a good fit for Spot Instances, then you can reap the benefits of Spot Instance pricing. Spot Instances are more cost-effective than Dedicated, On-Demand, or Reserved Instances, and the 2-hour application runtime makes it a good candidate for Spot Instances. So, this is the key. Now, on to the distractors. First is A, Dedicated Instances, which is an incorrect response. Dedicated Instances are Amazon EC2 instances that are run in a VPC on hardware that's dedicated to a single customer. Dedicated Instances that belong to different AWS accounts are physically isolated at a hardware level, and this extra level of isolation costs more than regular On-Demand Instances do. So, knowing the pricing implications of Dedicated Instances helps eliminate this response as a potential key. Next is, On-Demand Instances. On-Demand Instances are the most flexible option, but based on the stem, flexibility isn't what's being asked for. The stem is asking for the most cost-effective solution. On-Demand Instances are cost-effective, but with Spot Instances also being a potential response here, you know that this isn't the answer because Spot is more cost-effective, eliminating this response as a potential key. Lastly, we have C, Reserved Instances. Reserved Instances can give you up to 72-percent discount off of the On-Demand Instances. This makes it a potential answer here, but again, we're looking for the most cost-effective, and since the 2-hour runtime for the application makes Spot Instances a candidate, that means that Reserved Instances, though they are very cost-effective, they are not the most cost-effective. So, this is also an incorrect response.