How to Select the Right EC2 Instance: Complete Step by Step Guide
By Braincuber Team
Published on March 27, 2026
Selecting the right EC2 instance is crucial for optimizing costs and performance in your AWS infrastructure. This comprehensive step by step beginner guide will teach you how to choose the perfect EC2 instance by understanding instance types, families, generations, and sizing considerations.
What You'll Learn:
- Understanding EC2 instance components (compute, memory, storage)
- Five main AWS instance types and their use cases
- How to decode EC2 instance names and their components
- Step by step process for selecting the right instance
- Best practices for instance sizing and optimization
Understanding EC2 Instance Components
A good analogy for an EC2 instance is your work desk. Your brain is the compute, the surface of your desk is the memory, and your desk drawer is the storage. This analogy helps split the role of compute, memory, and storage in an EC2 instance.
Compute is concerned with parallelism – the ability to execute multiple tasks simultaneously. More CPU cores equals more parallelism which equals more compute power.
Memory is fast and volatile while storage is slow and non-volatile. Things kept on the surface of your desk are quickly accessible, like data in computer memory, but anything left overnight is at risk of being lost – just like volatile memory.
Five Main AWS Instance Types
When you select an instance type, you're effectively selecting for the lowest price per unit of the metric most important for your workload. This metric can be CPU/GPU performance, memory, or storage.
General Purpose
Balanced approach for compute, memory and networking. Ideal for web servers and applications with moderate resource requirements.
Compute Optimized
Lowest dollar cost per CPU core. Perfect for compute-intensive workloads like scientific modeling, gaming servers, and batch processing.
Accelerated Computing
Uses specialized GPUs for machine learning and high-performance computing workloads requiring massive parallel processing power.
Storage Optimized
High IOPS for large data reads/writes. Uses physically attached storage (instance store) for NoSQL databases like Elasticsearch and MongoDB.
Memory Optimized
Lowest dollar cost per unit of RAM. Ideal for in-memory databases, caches, and SQL databases requiring large amounts of memory.
Important: Storage optimized instances use physically attached storage (instance store) that doesn't persist beyond the instance life. If the instance stops, hibernates, terminates or fails, you lose all data on that instance.
Anatomy of an EC2 Instance Name
EC2 instance names like t2.nano, r6a.large or i3en.6xlarge contain important information about the instance. Let's break down a complex name like i3en.6xlarge.
| Component | Example | Meaning |
|---|---|---|
| Instance Family | i | Storage optimized instance family |
| Generation | 3 | Third generation (higher = newer) |
| Special Features | en | Extra capacity + network optimized |
| Size | 6xlarge | 6 times larger than xlarge |
Instance Family
The first letter indicates the instance family. Each family belongs to only one instance type (general purpose, compute optimized, etc.). As you work more with AWS, this becomes second nature.
Instance Generation
The number shows the instance generation. Higher numbers mean more recent generations. Always select the latest generation when possible - they typically offer better cost per unit of performance.
Special Features
Optional letters after the generation denote special features. These come at extra cost, so only select them if needed:
a – AMD processors
g – AWS Graviton processors
i – Intel processors
d – Instance store volumes
b – Block storage optimization
z – High frequency
e – Extra capacity (RAM or storage)
n – Network optimized (high bandwidth)
Instance Size
The size appears after the full stop, ranging from nano to xlarge. The number only appears with xlarge instances and acts as a multiplier. For the same instance type, the size multiplies compute (vCPUs), memory (RAM), and storage capacity.
Size Multiplier Example
An i3en.xlarge has 4 vCPUs, 32 GiB memory, and 2500 GB storage. An i3en.6xlarge is six times larger: 24 vCPUs, 192 GiB memory, and 15,000 GB storage.
Complete Step by Step Selection Process
Select Instance Type
Choose between general purpose, compute optimized, accelerated computing, storage optimized, or memory optimized. This is the most important decision - optimize for the lowest dollar cost per unit of the metric most important to your workload.
Select Instance Family
Check the technical documentation for your application and use their recommended instance family. For example, Elasticsearch recommends the "i" family (specifically i3). The application developers have done the testing for you.
Select Special Features
Only choose instances with special features if absolutely needed. These features come at extra cost, so avoid them unless your workload specifically requires them.
Select Instance Size
Run tests while monitoring CPU and memory utilization to determine appropriate size. Provide headroom for peak demand - 90% utilization is bad, 80% is acceptable, 70% and below is good.
Always choose the latest generation when possible. Latest generation instances typically offer better cost per unit of performance compared to older generations.
Frequently Asked Questions
What's the difference between EBS and instance store?
EBS volumes are persistent network-attached storage that survives instance termination. Instance store is physically attached storage that's faster but doesn't persist when the instance stops.
Should I always choose the latest generation instance?
Generally yes, as latest generations offer better cost per performance. However, check if your applications are compatible and if the specific features you need are available.
How do I know if my application needs special features?
Check your application documentation and requirements. Features like network optimization or extra storage are only worth the cost if your workload specifically benefits from them.
What CPU utilization level should I target?
Target 70% or below for good headroom. 80% is acceptable, but 90% utilization is too high and risks performance issues during peak demand.
Can I change instance types after launching?
Yes, you can change instance types within the same family, but you cannot change between different instance families (like from general purpose to compute optimized).
Need Help with AWS EC2?
Our cloud experts can help you optimize your EC2 instances for maximum performance and cost efficiency.