Amazon Web Services

AWS On-Demand Instance:

AWS On-Demand Instance (Amazon Web ServicesOn-Demand Instances) are virtual servers that run in AWS Elastic ComputeCloud(EC2) or AWS Relational Data base Service (RDS) and are purchased at afixed rate per hour.AWS recommends using On-Demand Instance for applicationwith short-term, irregular workloads that cannot be episodic. They are alsosuitable for use during testing and maturity of applications on EC2.

AWS ec2 Instance are designed for different tasks within the cloud. On-Demand Instances have no bond pledge AWS EC2 Instance are presented in a variety of different levelsof compute power and and can be launched as needed -- except potentially duringperiods of very high compute demand in particular availability zones. This is usuallythe most classy purchasing option for AWS instances, though exact hourly pricesvary depending on the operating system and size of the instance. Each On-DemandInstance is billed per instance hour from time it is launched until it is finishedor stopped. Partial instance hours are rounded up to the full hour uponbilling. A free tier of usage is also available.

Spot Instances:

A Spot Instance is anunused EC2 instance that is available for less than the On-Demand price.Because Spot Instances enable you to request unused EC2 instances at steepdiscounts, you can lower your Amazon EC2 costs significantly. The hourly pricefor a Spot Instance is called a Spot price. The Spot price of each instancetype in each Availability Zone is set by Amazon EC2, and adjusted gradually basedon the long-term supply of and demand for Spot Instances. Your Spot Instanceruns whenever capacity is available and the maximum price per hour for yourrequest exceeds the Spot price.

Spot Instances are a cost-effective choice if you can be flexible about when your applications run and if your applications can be interrupted. For example, Spot Instances are well-suited for data analysis, batch jobs, background processing, and optional tasks.

One strategy tomaintain a minimum level of guaranteed compute resources for your applicationsis to launch a core group of On-Demand Instances, and supplement them with SpotInstances when the opportunity arises.

Another strategy is to launch Spot Instanceswith a specified duration (also known as Spot blocks), which are designed notto be interrupted and will run continuously for the duration you select. Inrare situations, Spot blocks may be interrupted due to Amazon EC2 capacityneeds. In these cases, we provide a two-minute warning before we terminate aninstance, and you are not charged for the terminated instances even if you usedthem.

Reserved Instances:

Reserved Instances provide you with a significant discount compared to On-Demand Instance pricing. Reserved Instances are not physical instances, but rather a billing discount applied to the use of On-Demand Instances in your account. These On-Demand Instances must match certain attributes in order to benefit from the billing discount.

Thefollowing diagram shows a basic overview of purchasing and using ReservedInstances.

In this scenario, you have a running On-DemandInstance (T2) in your account, for which you're currently paying On-Demandrates. You purchase a Reserved Instance that matches the attributes of yourrunning instance, and the billing benefit is immediately applied. Next, youpurchase a Reserved Instance for a C4 instance. You do not have any runninginstances in your account that match the attributes of this Reserved Instance.In the final step, you launch an instance that matches the attributes of the C4Reserved Instance, and the billing benefit is immediately applied.