How to Choose Amazon EC2 Instances - Optimizing Instance Families and Purchase Options
Understand the characteristics of instance families and the performance advantages of Graviton processors, along with guidelines for choosing between On-Demand, Reserved, and Spot purchase options.
Overview of EC2
EC2 is a compute service that provides virtual servers in the cloud. You can choose from over 1,000 instance types (as of October 2026) based on your use case and launch servers in minutes. While Lambda is an event-driven serverless compute service, EC2 is suited for workloads that require OS-level control. Instances powered by Graviton processors, the Arm-based CPUs designed by AWS, are also available to choose within the same EC2 according to your use case.
Instance Families and Purchase Options
The M family (general purpose) is suited for web servers and application servers, the C family (compute optimized) for batch processing and scientific computing, and the R family (memory optimized) for in-memory caches and databases. Graviton processors are Arm-based CPUs designed by AWS. The official AWS description as of August 2026 states that, compared with equivalent x86-based EC2 instances, they cost up to 20% less and use up to 60% less energy. Spot Instances use EC2 spare capacity at up to 90% discount, with a 2-minute interruption notice to safely execute shutdown procedures.
Graviton Instances and Choosing a Generation
AWS Graviton processors have gone through several generations, and the instances powered by them have grown in number accordingly. Graviton2 debuted in December 2019 along with M6g, C6g, and R6g, Graviton3 started with C7g in November 2021, and Graviton4 powers eighth-generation instances such as R8g and M8g. The official AWS description as of August 2026 states that Graviton-powered instances cost up to 20% less and use up to 60% less energy compared with equivalent x86-based EC2 instances. The frequently cited figure of "up to 40%" was presented when the Graviton2 generation was announced, and it is not a value that applies as is to later generations. Because newer-generation instance types roll out to Regions gradually, check in the EC2 console or the official list of instance types whether you can actually choose them in the Region and size you want. Major runtimes including Java, Python, and Node.js support Arm64, making migration possible for many workloads. For container workloads, building multi-architecture images enables execution on both x86 and Graviton. Newer-generation instances offer improved network bandwidth and EBS throughput over previous generations, and in some cases you can meet the same performance requirements with a smaller instance size. Select compute optimized (C family), memory optimized (R family), or general purpose (M family) based on your workload characteristics.
Purchase Options and Cost Optimization
The main EC2 purchase options are On-Demand, Reserved Instances (RI), Savings Plans, and Spot Instances. In addition, Dedicated Hosts, which give you a dedicated physical server, and On-Demand Capacity Reservations, which reserve capacity only for the period you need, are also available. There are two types of Savings Plans: Compute Savings Plans and EC2 Instance Savings Plans. Compute Savings Plans apply across EC2, Fargate, and Lambda, and flexibly accommodate changes in instance family or region. A 1-year or 3-year commitment provides discounts of up to 66%. EC2 Instance Savings Plans narrow their use to a specific instance family in a specific Region, and in return a higher discount rate applies. Spot Instances offer up to 90% discount but require designs that handle the 2-minute interruption notice. RIs come in two offering classes, Standard and Convertible, which differ in the scope that is fixed. Standard RIs fix the instance family and Region at the time of purchase, but you can change the size within the same family. Convertible RIs keep the Region fixed, but they allow exchanges for a different configuration, including the instance family, OS, and tenancy. Because Standard offers the higher discount rate, Standard suits workloads whose configuration will not change for a long time, and Convertible suits cases where you want to leave room for future changes. Cost Explorer recommendations let you check the optimal combination of purchase options based on your current usage patterns.
Choosing by Workload
EC2 instance families are divided by the kinds of processing they excel at. There are general-purpose types for uses where the balance between CPU and memory matters, such as web servers and applications, and CPU-focused types suited to compute-heavy processing. There are also memory-focused types for databases and caches that load large amounts of data into memory, and accelerated computing types used for machine learning and graphics processing. The starting point is to identify which resource your workload needs most and choose a family that matches it. By choosing an instance that is well provisioned in the resource that becomes the bottleneck, you can get the performance you need without waste.
Right-Sizing and Scaling
If you choose an instance that is too large out of fear of insufficient performance, you waste money. Conversely, if it is too small, processing is delayed. It is important to right-size by measuring actual usage and adjusting to a size that matches CPU and memory utilization. Using tools that analyze usage and present recommendations makes it easier to find over-provisioning and under-provisioning. For workloads with large fluctuations in load, combine scaling that automatically increases and decreases the number of instances according to demand, and handle the load with the number of instances. Distributing across multiple instances is often more advantageous than scaling up an individual instance, in terms of both availability and cost efficiency.
Choosing Storage and Networking
Instance performance depends not only on CPU and memory but also on storage and networking. Persistent disks come in types for different uses, and you choose based on the balance between the performance you need (throughput and IOPS) and cost. Some processing benefits from temporary, fast local storage. For network-intensive workloads, instances that support high-speed networking and placement arrangements for low-latency communication make a difference. Considering the configuration including the data input and output paths, rather than focusing only on compute resources, is the key to getting the expected performance.
Best Practices for Operations and Migration
To operate EC2 efficiently, it is important to make configurations reproducible. If you prepare images and launch templates configured in advance, you can start up instances with the same configuration quickly, which makes scaling and disaster recovery easier. Apply OS and software updates in a planned way with management tools. From a cost-reduction perspective, migrating to newer generations or to instances that use more power-efficient processors pays off. In many cases, you can get equal or better performance at a lower cost. Migrating in a planned way to more efficient instances after verifying compatibility leads to long-term optimization.
Summary
EC2 builds optimal computing environments through combinations of instance families, sizes, and purchase options. Improve cost-performance with Graviton instances, and optimize costs while meeting performance requirements by combining Savings Plans with Spot Instances.
References (Official AWS Resources)
The primary sources for this page are the official AWS website and documentation. Check the official pages below for the latest specifications and pricing.
- Amazon EC2 official page
- AWS Auto Scaling official page
- Amazon EBS official page
- AWS Documentation (official)
If this page and the official documentation disagree, treat the official documentation as authoritative.