For example, we have 10 t3.medium ec2 instance. Let's say that there are 6 always running 24/7, but the other 4 are not running 24/7, they are turned off when not in use.
If I buy a reserved instance for t3.medium, how does AWS know to apply it to the instances running 24/7 and not part time?
Amazon doesn't apply reserved pricing to a specific instance at all. It basically just applies reserved pricing to your bill. It's like a discount at the time your bill is processed. If you have reserved pricing for N instances, and you have at least N instances running 24/7 reflected in your bill, then the reserved pricing gets applied to those N instances.
Amazon doesn't really care if you are running a single specific instance 24/7, or deleting and recreating instances once a minute. In the end it's just the total number of seconds you have a specific type of instance running each month that they care about, and bill you for.
Be aware that when you setup instance reservations it is actually a capacity reservation. You are telling Amazon you are committing to running this type of instance 24/7 for either 1 year or 3 years. By letting Amazon know this, it helps with their capacity planning, and in return they give you a cost discount. But it also means that they are going to charge you for that reserved capacity even if you don't actually have that instance running 24/7.
Answer from Mark B on Stack OverflowServeTheHome
servethehome.com › news › amazon aws ec2 reserved instance pricing: a major change
Amazon AWS EC2 Reserved Instance Pricing: A major change
December 3, 2014 - Amazon Web Services (AWS) EC2 just made a major change to its reserved instance pricing: the potential to eliminate up-front costs. Reserved instances provide a lower price for agreeing to utilize a certain amount of capacity for years. Previously, reserved instances had hefty up-front costs which could cost more than purchasing and setting up similar or faster hardware in a datacenter.
AWS
aws.amazon.com › amazon ec2 pricing › reserved instances › pricing
EC2 Reserved Instance Pricing
2 days ago - With the Partial Upfront option, you make a low upfront payment and are then charged a discounted hourly rate for the instance for the duration of the Reserved Instance term. The No Upfront option does not require any upfront payment and provides a discounted hourly rate for the duration of ...
amazon web services - How does AWS know to apply reserved instances price to the EC2 running 24/7 and not part time? - Stack Overflow
Our organization has many EC2 on-demand instances. We never looked at the reserved instance pricing because we thought we had to pay up-front. But I see that now there are reserved instance with no... More on stackoverflow.com
Modeling EC2 on-demand vs reserved instance pricing
Well, thanks! Switching to a reserved instance just saved my small nonprofit $240 a year. More on reddit.com
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May 16, 2023Reserved Instance
A t2.small on demand instance costs $0.023/hour , about $16.75/month. If you are running in unlimited burstable mode, that adds on $0.05/hour, bringing the cost up to about $75.00 a month. You will reduce this amount by about 30% buying a reserved instance. You probably have $400/month in outbound data transfer costs, storage used. Those items aren’t reduced by purchasing a reserved instance or savings plan. Look at all of the line details on your last bill, you should be able to find out what other components are causing this cost. More on reddit.com
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December 12, 2024automatic EC2 Reserve pricing calculator + report
Haven’t used it myself, so it might not be exactly what you are looking for (I know, risky recommending stuff without hands-on experience…), but this sounds a lot like https://aws.amazon.com/compute-optimizer/ ? You’d need to toggle on “include reserved instances” explicitly, but then it might be useful for doing what you are trying to achieve - and do it beyond just EC2 instances? More on reddit.com
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July 24, 2024Videos
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Amazon/AWS EC2 Pricing Simply Explained | On-Demand, Spot, Reserved, ...
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How Much Does an AWS EC2 Instance Cost Per Month & Pricing Per ...
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EC2 Instance Purchasing Options Overview - YouTube
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What is an Amazon EC2 Reserved Instance? - YouTube
Amazon Web Services
aws.amazon.com › cloud financial management › cost optimization with aws › reserved instances
Reserved Instances
2 days ago - You can make rightsizing a smooth ... monitoring and analysis. ... Amazon EC2 Reserved Instances (RI) provide a significant discount (up to 75%) compared to On-Demand pricing and provide a capacity reservation when used in a specific Availability Zone....
AWS
aws.amazon.com › what is cloud computing? › cloud comparisons hub › compute › what’s the difference between on-demand instances and reserved instances?
On-Demand Instances vs Reserved Instances - Instance Types Comparison - AWS
2 days ago - The Amazon EC2 Reserved Instances Marketplace allows customers to buy and sell existing AWS Reserved Instances. The cost to buy a Reserved Instance with a partial term left may be significantly lower than the cost to buy outright.
Parquantix
parquantix.com › helpful guide to aws reserved instance pricing options
Understanding AWS Reserved Instance Payment Options
May 4, 2021 - AWS Reserved Instances is a pricing option that can reduce cloud costs by up to 60%, compared to on-demand rates. For computing services, like Amazon EC2, and database services, like Amazon RDS and ElastiCache, you can reserve a set number of ...
Reddit
reddit.com › r/devops › modeling ec2 on-demand vs reserved instance pricing
r/devops on Reddit: Modeling EC2 on-demand vs reserved instance pricing
May 16, 2023 -
Managing cloud costs can be quite complex. You've got to predict the future while understanding how pricing structures impact all possible load patterns. In this post I discuss a how re-framing on-demand instances as a "premium" instead of reserved instances as a "discount" can shift your thinking. There's a break even point at around 15 hours per day when on-demand and reserved instance pricing meet (across almost all instance types). I walk through how to calculate costs and model costs in a formal way. This can help you save the most money when auto-scaling.
Amazon Web Services
docs.aws.amazon.com › amazon ec2 › user guide › amazon ec2 instances › amazon ec2 billing and purchasing options › reserved instances for amazon ec2 overview › regional and zonal reserved instances (scope)
Regional and zonal Reserved Instances (scope) - Amazon Elastic Compute Cloud
The scope does not affect the price. You pay the same price for a regional or zonal Reserved Instance. For more information about Reserved Instance pricing, see Key variables that determine Reserved Instance pricing and Amazon EC2 Reserved Instances Pricing
Amazon Web Services
docs.aws.amazon.com › amazon ec2 › user guide › amazon ec2 instances › amazon ec2 billing and purchasing options › reserved instances for amazon ec2 overview › how billing works with reserved instances
How billing works with Reserved Instances - Amazon Elastic Compute Cloud
For information, see AWS Free Tier ... Reserved Instances are billed for every clock-hour during the term that you select, regardless of whether an instance is running. Each clock-hour starts on the hour (zero minutes and zero seconds past the hour) of a standard 24-hour clock.
AWS
docs.aws.amazon.com › pdfs › whitepapers › latest › cost-optimization-reservation-models › cost-optimization-reservation-models.pdf pdf
cost-optimization-reservation-models.pdf
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CloudySave
cloudysave.com › aws › ec2 › understanding-aws-ec2-reserved-instances
Understanding AWS EC2 Reserved Instances - CloudySave
January 28, 2020 - To get the most out of them, however, ... bundles of services purchased in advance for a discount. This can be anything up to 75% on the on-demand price......
CloudOptimo
cloudoptimo.com › home › blog › aws savings plan vs reserved instances
AWS Savings Plan vs Reserved Instances
March 13, 2025 - This spending commitment allows AWS to offer substantial discounts, typically up to 72%, automatically applied to qualifying workloads. Discounts are applied automatically to qualifying workloads, encompassing Amazon EC2 instances, AWS Fargate, ...
nOps
nops.io › blog › on-demand-reserved-spot-dedicated-which-is-best-aws-ec2-pricing-option
On-Demand, Reserved, Spot, and Dedicated: Which Is the Best AWS EC2 Pricing Option?
May 2, 2024 - There isn’t an outright EC2 pricing option. It all depends on your workload and business goals. If you don’t like making a huge upfront cost for a long-term commitment, use On-Demand Spot Instances. With On-Demand, you can run temporary processes on test environments. For reliable performance, use Reserved Instances.
PTP
ptp.cloud › home › aws cost savings plans vs reserved instances explained
AWS Cost Savings Plans vs Reserved Instances Explained
March 26, 2021 - What is the difference between AWS Savings Plans and Reserved Instances? Savings Plans discount a committed spend and apply across eligible services. Reserved Instances discount specific EC2 instance families in a region. Savings Plans are more flexible.
Medium
medium.com › @info-31059 › aws-cost-optimization-reserved-instances-2-1bbb8d082921
AWS Cost Optimization — Reserved instances EC2
December 7, 2022 - The discounts can range from 27% to 72%, depending on the selected options. The need for better pricing models for longer-term workloads is why AWS launched reserved instances in 2009 because building a cost-optimized environment on AWS is a ...
DEVCLASS
devclass.com › home › serverless › aws debuts lambda managed instances on ec2: more control, lower cost for...
AWS debuts Lambda managed instances on EC2: more control, lower cost for high volume users • DEVCLASS
3 weeks ago - Lambda managed instances are a ... exact EC2 instance type used and get discounted prices in return for commitments using compute savings plans or reserved instances. Each instance can handle multiple concurrent requests. These instances are only used for Lambda, and are managed automatically with operating system updates, load balancing, and a maximum lifetime of 14 days. Users define what AWS calls a capacity ...
Amazon EC2
instances.vantage.sh
Amazon EC2 Instance Comparison
Reserved/Savings Plan1-year - No Upfront · CurrencyUnited States Dollar ($) ColumnsColumns · CompareClear Filters · Export · Updated 12/19/2025, 8:14:00 AM · EC2Instances.info - Easy Amazon EC2 Instance Comparison ·
AWS
aws.amazon.com › amazon ec2 › pricing › on-demand pricing
EC2 On-Demand Instance Pricing
2 days ago - To see prices, visit the Elastic Load Balancing page. On-Demand Capacity Reservations are priced exactly the same as their equivalent (On-Demand) instance usage. If a Capacity Reservation is fully utilized, you only pay for instance usage and nothing towards the Capacity Reservation.
GeeksforGeeks
geeksforgeeks.org › cloud computing › introduction-to-amazon-web-services
Introduction to Amazon Web Services - GeeksforGeeks
1 week ago - This offers: Up to 75% cost savings compared to on-demand pricing. Flexible payment options (All upfront, Partial upfront, or No upfront). Spot Instances allow you to bid on unused EC2 capacity.
How-To Geek
howtogeek.com › home › cloud › how much cheaper are aws-reserved instances?
How Much Cheaper Are AWS-Reserved Instances?
August 5, 2020 - If you know you're going to be using an EC2 instance for a long time, you can commit to a yearly contract to buy the instance at a huge discount when compared to the On-Demand price. Reserved Instances have two options---term length and how much you pay up front, with a longer term length and a larger upfront payment obviously costing less. You also have the option of convertible plans, which we discuss more soon. You can view prices for any instance type yourself using AWS's Simple Monthly Calculator.