When creating an Amazon EC2 instance, you always start by choosing a base Amazon Machine Image (AMI). An AMI contains the operating system, settings, and other applications needed for your server. AWS provides pre-built AMIs, and you can also use custom AMIs or those sold on the AWS Marketplace. Note that AMIs cannot be modified after launch.

After choosing your AMI, you select the instance type and size. This determines the physical properties of your instance, including CPU, RAM, and network speed. Your choice depends entirely on your workload. You can freely modify your instance type even after launch, a process commonly known as "right-sizing".