AWS Instance Types: How to Choose the Best Option for Your Use Case

07-02-2025 / Cost Optimization Strategies / 10 mins.

AWS Instance Types: How to Choose the Best Option for Your Use Case

You might wonder how companies using Amazon Web Services (AWS) waste more than $10 billion dollars annually. It's easy to ask yourself: "Why don't they just cut their spending?"

Well, it's because there's more to consider. AWS offers many options: more than 200 different services, for example. Amazon Elastic Compute Cloud (EC2) provides more than 300 AWS instance types spread across five unique instance families.

It's understandable that choosing which AWS instance family to use can feel overwhelming. You're not alone.

  • In 2020, companies wasted around $17 billion on AWS. The main causes of waste were idle compute resources and oversized AWS instances.
  • Around 40% of instances are at least one size larger than necessary for the workloads they handle.

However, downsizing an instance by one level can reduce its cost by 50%, so choosing the right instance size and type is crucial for optimizing your AWS costs.

This guide aims to help you decide which instance type is right for your organization. It includes when to use each type and what factors you should consider.

You might wonder how companies using Amazon Web Services (AWS) waste more than $10 billion dollars annually. It's easy to ask yourself: "Why don't they just cut their spending?"

Well, it's because there's more to consider. AWS offers many options: more than 200 different services, for example. Amazon Elastic Compute Cloud (EC2) provides more than 300 AWS instance types spread across five unique instance families.

It's understandable that choosing which AWS instance family to use can feel overwhelming. You're not alone.

  • In 2020, companies wasted around $17 billion on AWS. The main causes of waste were idle compute resources and oversized AWS instances.
  • Around 40% of instances are at least one size larger than necessary for the workloads they handle.

However, downsizing an instance by one level can reduce its cost by 50%, so choosing the right instance size and type is crucial for optimizing your AWS costs.

This guide aims to help you decide which instance type is right for your organization. It includes when to use each type and what factors you should consider.

What are AWS Instances?

An AWS instance is a virtual machine on the AWS platform that you can use to run cloud-based applications. Instead of buying a physical computer or server, you can use a cloud-based environment. Renting compute capacity on AWS can improve your costs, time to market, and time to value.

Instances differ in the CPU, RAM (memory), storage, and network capacity they offer. This is especially true with Amazon EC2.

Instances are virtualized, so you can dynamically scale compute capacity up or down to match the peak and valley demands your business generates. This auto-scaling feature gives EC2 its name: "Elastic." EC2 is the most widely used compute service in AWS, although there are 12 others.

The amount you pay will depend on the instance type you use in AWS.

AWS Instance Families: What Are the Different Instance Types?

We mentioned that instances are virtual servers. Like any virtual server, AWS instances run on a host machine. AWS offers virtually unlimited virtual host machines with diverse compute resources (CPU, RAM, storage, and bandwidth).

Different instances have different levels of compute resources, so some are better suited for specific workloads than others. AWS instances are grouped into different families. You can identify instance types by looking at their names, which consist of a letter, a number, and sometimes an additional letter.

What Do the Letters and Numbers in AWS Instances Mean?

The first letter is generally uppercase and indicates which family the AWS instance belongs to. It is followed by a number that indicates which generation the instance belongs to. The characteristics of families and generations vary. A lowercase letter after that number typically shows how AWS has optimized that instance type.

The letters include A, B, C, D, E, F, G, H, M, P, R, T, and X. AWS instance generations range from 1 to 6. For example, C4 refers to AWS instances in the fourth generation of the C family of AWS instances.

Instances in AWS are generally from the current generation. Additionally, there are low-cost alternatives based on previous-generation instances. These include:

Instance Type

Available Size

A1

a1.medium, a1.large, a1.xlarge, a1.2xlarge, a1.4xlarge, a1.metal

C1

c1.medium, c1.xlarge

C3

c3.large, c3.xlarge, c3.2xlarge, c3.4xlarge, c3.8xlarge

G2

g2.2xlarge, g2.8xlarge

I2

i2.xlarge, i2.2xlarge, i2.4xlarge, i2.8xlarge

M1

m1.small, m1.medium, m1.large, m1.xlarge

M2

m2.xlarge, m2.2xlarge, m2.4xlarge

M3

m3.medium, m3.large, m3.xlarge, m3.2xlarge

R3

r3.large, r3.xlarge, r3.2xlarge, r3.4xlarge, r3.8xlarge

T1

t1.micro

This last option is a good alternative for workloads with low performance requirements. Even so, you can select the most energy-efficient types to save money. However, what you need is a balanced provisioning strategy.

When Should You Use Each Instance Type?

AWS offers five different instance types, and the name of each family describes its recommended use case, as shown below:

  • General Purpose
  • Compute Optimized
  • Memory Optimized
  • Accelerated Computing
  • Storage Optimized

Below is an overview of each instance family, including their characteristics and typical ideal use cases.

1. AWS General Purpose Instances

(Mac, T4g, T3, T3a, T2, M7g, M6g, M6i, M6in, M6a, M5, M5a, M5n, M5zn, M4, A1)

These instances offer a balanced amount of processing power for a wide variety of scalable use cases:

  • A (a1.medium, a1.large, a1.xlarge, etc.): Arm-based instances that use AWS Graviton processors, optimized for EBS (high-performance storage) and with support for enhanced networking.
  • Mac (mac1.metal, mac2.metal): Designed to handle workloads on Apple operating systems in Xcode IDE.
  • T (T4g, T3, T3a, T2): Support a "burstable" mode to handle CPU usage spikes.
  • M (M7g, M6g, M6i, etc.): Suitable for small and medium-sized databases and enterprise applications.

2. AWS Compute Optimized Instances

(C7g, C7gn, C6i, C6in, etc.)

Ideal for use cases that require high compute power, such as:

  • High-performance web servers
  • Media transcoding
  • Scientific modeling
  • Batch processing

These instances are more cost-effective even for intensive tasks, with newer generations like C6g offering significant improvements thanks to Graviton2 processors.

3. AWS Memory Optimized Instances

(z1d, High-memory, X1, R5, R6g, etc.)

Designed for memory-intensive workloads:

  • R family: Ideal for large datasets, data mining, and analytics.
  • X family: For high-performance databases such as HANA and SAP.

4. AWS Accelerated Computing Instances

(Vt1, F1, G3, G4ad, DL1, etc.)

Deliver sustained performance through the use of hardware accelerators:

  • P: Intensive processing such as machine learning and seismic analysis.
  • DL: Deep learning model training with up to 40% better price-performance ratio.
  • G: Graphics-intensive applications such as 3D rendering and video encoding.

5. AWS Storage Optimized Instances

(H1, D2, D3, I3, etc.)

Ideal for large data volumes:

  • D: High-volume persistent storage.
  • H1: High disk throughput.
  • I3: NVMe SSD-based storage for low-latency needs.

Factors to Consider When Choosing the Right AWS Instance Type

Fixed Performance vs. Burstable Performance

  • Burstable: Allow you to handle temporary CPU usage spikes while keeping costs low.
  • Fixed: Provide consistent performance and are ideal for applications with sustained high demands.

For example, for small databases or web servers, burstable instances are suitable, while for video encoding or high-volume websites, fixed-performance instances are the best option.

What Instance Sizes Are Available?

AWS instance types come in a range of sizes, these include:

  • Nano
  • Micro
  • Small
  • Medium
  • Large
  • XLarge
  • 2XLarge
  • 4XLarge
  • 6XLarge
  • 8XLarge
  • 16XLarge
  • 32XLarge

AWS Relational Database Storage Instances (Amazon RDS)

In addition to Amazon EC2, there are other AWS services with instances worth considering. AWS Relational Database Storage (Amazon RDS) offers three instance types based on memory and processing power requirements:

  • General Purpose (db.M4, db.M5, db.M6g)
  • Memory Optimized (db.R4, db.R5, db.R6g, db.X1, db.X1e, db.z1d)
  • Burstable (db.T2, db.T3)

Just like Amazon EC2 instances, RDS instances are available in various sizes. They need to be rightsized to avoid exceeding your AWS budget.

What About AWS Instance Pricing?

Amazon EC2 offers four paid pricing options and a free tier. The free tier requires you to use only AWS Micro instances, with a maximum of 750 hours of t2.micro instances on Linux or Windows.

If you use paid instances, AWS updates its pricing frequently, so it's important to check the official Amazon EC2 instance pricing page.

Here is a summary of how Amazon EC2 pricing works:

On-Demand Instances

They allow you to scale compute resources based on your application's needs.

  • You pay by the hour or by the second, with no minimum usage threshold.
  • Keep in mind that EC2 instances are always active, so AWS will continue to charge you until you stop them.

This option is suitable for applications with unpredictable resource usage at different times.

Spot Instances

They allow you to access Amazon EC2's excess capacity at up to one-tenth the cost of an On-Demand instance.

  • Prices depend on the number of unused instances in AWS and demand.
  • They are typically available during low-demand periods, so you will need to run your instances at those times to take advantage of them.

AWS can reclaim the instances with just a two-minute warning. However, you can pause and resume your work later. These instances are ideal for fault-tolerant workloads, or you can use a tool like Xosphere, which automatically optimizes your workloads between Spot and On-Demand instances depending on the price.

AWS Savings Plans

They allow you to commit to a specific monthly spend rather than a particular instance type or family, in exchange for discounts of up to 72% compared to On-Demand rates.

  • You can use your Savings Plan instances with other AWS compute services, such as AWS Lambda functions and AWS Fargate.

Dedicated Hosts

They provide a physical EC2 server for your exclusive use.

  • You can purchase the plan on-demand or as an AWS reservation with discounts of up to 70% off the On-Demand price.
  • It is ideal if you need to meet specific compliance regulations.

Per-Second Billing

It is one of the fairest options, as you only pay for what you use.

  • Unlike On-Demand billing, you are not charged for the seconds or minutes your instances are idle.

At Frust We Help You Rightsize Your EC2 Instances

Frust conducts an assessment of your consumption patterns, instance types, and families to calculate and develop the best plan to help you generate savings on your AWS costs.

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