![]() ![]() Once you purchase a reserved instance, you have guaranteed access to EC2 resources at a set price. Reserved instances are, however, more convenient and predictable than spot instances because you do not have to invest time in bidding on a reserved instance, or trying to predict when prices will be lowest. Reserved instances provide discounts of up to 75 percent compared to on-demand instances, rather than the 90 percent discounts of spot instances. Reserved-instance rates are lower than on-demand pricing, although the discounts are not as great as those of spot instances. When you choose a reserved instance, you purchase a certain amount of EC2 resources ahead of time. Reserved instances are another way to get an Amazon EC2 instance pricing discount. However, if you know that you are going to host a particularly resource-intensive workload for a temporary period and have flexibility regarding when that workload is run, or if you have free time available to bid on spot instances, this Amazon EC2 instance pricing model can deliver the greatest EC2 cost savings. If you manage many EC2 instances, it is simply not realistic to attempt to take advantage of spot-instance pricing for all of them. ![]() Spot instance pricing is not a good option for Amazon EC2 workloads that you run an on an ongoing basis because spot instances are less predictable, and the work required to bid on spot instances is significant. You also have no way of knowing whether your bid will be accepted.ĪWS provides a tool called Bid Advisor to help you plan spot instance bids, which is useful if you wish to take advantage of spot instance pricing, but there is still no way to predict with certainty when spot instances will be at the lowest price. The disadvantage is that, in order to take good advantage of this type of Amazon EC2 instance pricing, you have to bid on spot instances when discounts are high. The advantage of spot instances is cost savings, which, again, can be very significant if you bid at the right time. Discounts can be as high as 90 percent off of the equivalent on-demand pricing. The size of the discount, as well as the likelihood of winning your bid, vary depending on the level of demand that exists for resources on EC2 at a given moment. Spot instances, unlike on-demand pricing, can provide significant discounts for EC2 costs. With spot instances, you can issue a bid to purchase EC2 resources at a discounted rate. However, on-demand pricing is the most easily managed and predictable type of Amazon EC2 instance pricing, especially for applications that experience constant fluctuations in demand, such as high-traffic Web servers. The major downside of on-demand pricing is that it is more expensive than most other EC2 pricing models because it does not provide an opportunity to gain a discount. Thus, if your EC2 instance consumes a large amount of compute for a few hours per day, but less compute at other times, your costs will vary proportionally. You pay only for the amount of resources that you actually use. With this types of Amazon EC2 instance pricing, you will have immediate access to as much compute, memory and storage as you need, even if their resource requirements fluctuate frequently. EC2 on-demand pricing model is the most basic type of EC2 pricing. ![]()
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