You have a video transcoding application running on Amazon EC2. Each instance polls a queue to find out which video should be transcoded and then runs a transcoding process. If this process is interrupted, the videos will be transcoded by another instance based on the queuing system. You have a large backlog of videos that need to be transcoded and reduce this backlog by adding more instances. You will need these instances only until the backlog is reduced. Which type of Amazon EC2 instances should you use to reduce the backlog in the most cost-efficient way?

Answer options:

A.Reserved instances
B.Spot instances
C.Dedicated instances
D.On-demand instances

Answer – B
Since this is like a batch processing job, the best type of instance to use is a Spot instance. Since these jobs don’t last for the entire duration of the year, they can bid upon and be allocated and deallocated as requested.
Options A and C are incorrect because the application needs the instances only until the backlog is reduced. With reserved/dedicated instances, there is a possibility that the instances might get idle after the backlog reduction. So, this is a costly solution.
Option B is CORRECT because (i) they are less expensive than reserved instances, (ii) interruption in the transcoding process is affordable since another instance will transcode the videos based on the queuing system.
Option D is incorrect because (i) on-demand instances are most expensive, (ii) you can afford an interruption in the transcoding process, and (iii) on-demand instances would have been suited if there was no alternate way of transcoding the videos and interruption was not affordable.
For more information on Spot Instances, please visit the URL –
https://aws.amazon.com/ec2/spot/