EC2 Spot instance provides discount rate up-to 90% compared to normal on-demand instances price. Therefore running your fault-tolerant workloads on spot instance is one of quick ways to reduce your AWS Cost.
There are several ways to provision the spot instance. We can either use EC2 Spot Fleet Request or Auto Scaling Group.
AWS provides Spot Instance Advisor to help users determine which instance class is suitable to run their workloads.
By looking at the Spot Instance Advisor, user can see lists of instances with least chance of interruption and also the average amount of savings.
Looking at above example, we filtered instance with minimum count of vCPU and memory each 4 and 4 Gib. As we can see the highest savings over on-demand is m2.2xlarge with 90% average discount rate.
We can calculate the possible monthly savings if we use m2.2xlarge in spot for our fault-tolerant workloads compared with on-demand.
pricing in ap-southeast-1 region - $0.592 per Hour
on-demand:
hourly = 0.592
daily = 0.592 * 24 = 14.208
monthly = 4.208 * 30 = 426.24
spot:
hourly = 0.592 - (0.592 * 90%) = 0.0592
daily = 0.0592 * 24 = 1.4208
monthly = 1.4208 * 30 = 42.624
savings: 426.24 - 42.624 = 383.616