# Purchasing Options

There are 7 ways for puchasing options

1. On-Demand
2. Reserved
3. Saving Plans
4. Spot instance
5. Dedicated Hosts
6. Dedicated Instances
7. Capacity Reservations

### (1) On-Demand

It is a plan that pay for what you use .This plan has the `highest cost` but no upfront payment and long-term commitment.

#### Usecase

* short-term workload (because it is expensive plan)

### (2) Reserved

It is a plan that we need to specify instance attributes (Instance type , Region and OS) to be reserved.

the reservation period is `1 year` or `3 years.`It is  able to change the `instance type` and `OS` but need to pay more.

#### Usecase

* Database
* Steady-state usage applications

### (3) Saving Plan

It is similar to `Reserved` but we didn't reserve instance and more cheaper . we commit the certain type of usage such as ($10 / 1 hour for 1 or 3 years) If you spend EC2 more than this 1 hour in the day you need to pay in `On-demand`. This plan will lock to specific instance family and region.

#### Usecase

* longterm-usage (but we need to know limitation)

### (4) Spot Instance

This plan has different mechanism to get the instance. It is `most cost efficeint` instances  in AWS. You need to define `max spot price` if `current spot price` < `max spot price` , you will get the instance. If `current spot price` > `max spot price` , your instance will be stopped or terminated. It mean `you can lose your instance any point of time`.

#### Spot Block

It is the strategy that you can block the time 1 to 6 hours to make you instance can't be interrupt.

#### How to terminate Spot instance ?

Everytime we would like to have spot instance , we need to create spot request to define the spec and spot max price . Next when we want to terminate we command to terminate the instance but It will aumatically create new spot request so `you must first cancel a spot request and then terminate the associate spot instance`

#### Spot Fleets

It is a feature that allow us to automcatically request spot instances with the lowest price

#### Usecase

* Batch Job
* workload that are resilient to failure

### (5) Dedicated Host

It is plan to have your own physical server EC2 instance. It allow you to address `compliance requirements`. This is the most expensive option.

#### Usecase

* Softwarer that have complicated licensing model or for the companies that have strong regulatory or compliance needs

### (6) Dedicated Instances

Instance run on hardware that is dedicated to you.

### (7) Capacity Reservations

It reserve the instance and always have access to EC2 when you need it,  but you need to pay `On-demand` whether you run instances or not. (specific AZ)

#### Usecase

* short-term (workloads that needs to be in a specific AZ)