> For the complete documentation index, see [llms.txt](https://karansingh.gitbook.io/aws-saa-c02/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://karansingh.gitbook.io/aws-saa-c02/ec2/launch-types.md).

# Launch Types

## **On-demand Instances:**

* **For when you can't predict how long/short the job is** going to be and for **jobs which can't tolerate failure.**<br>
* **Pay-as-you-go**.<br>
* **Billing**:
  * **For Linux = billed every second, after the first minute.**
  * **All other operating systems = billed per hour.**

## **Reserved Instances:**

* **For steady usage apps** (like databases).
* **Long-term** (a **minimum of 1 year**).
* Has up to a **75% discount compared to on-demand**.<br>
* Can buy it for 1 year to 3 years
  * 3 years RI has a much higher discount than 1 year RI.<br>
* Can **pay all upfront, partially upfront and no upfront**.
  * All upfront has a much higher discount than no upfront.<br>
* There are also **2 other types of RIs:**
  * **Convertible RIs**
    * Can **change the type of instance type**, e.g. t2.micro to c5.large.
    * These have up to a **54% discount**.
  * **Scheduled RIs**
    * Can **launch within the time window you need them** but you still need to reserve it.

## **Spot Instances:**

* **If you can be flexible about when your applications run and if your applications can be interrupted.**
  * For example: image processing, batch jobs and any distributed workloads.<br>
* Have a **90% discount compared to on-demand**.
  * But that's because they **can be lost at any point of time** if someone else pays higher for it.

## **Dedicated Hosts:**

* **For companies with strict compliance requirements.**<br>
* It's a whole physical server dedicated to you.
  * **Very expensive.**<br>
* **Allocated for 3 years** so they need to be committed to.<br>
* **Access to the underlying hardware.**

## **Dedicated Instances:**

* They are **just dedicated hosts but you don't have access to the underlying hardware.**<br>
* **Pay by the hour.**


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