Picking EC2 instance types

It’s common to want to test infrastructure code that deploys EC2 instances into AWS. There are many different instance types, but not all instance types are available in all regions or availability zones (AZs). For example, t3.micro is sometimes available only in newer AZs, while t2.micro is sometimes only available in older AZs. If you are testing code that needs to deploy a “small” instance across many regions, this can make it tricky to know which region to pick.

To help work around this problem, Terratest includes:

1. GetRecommendedInstanceType: A Go function that helps you pick a recommended instance type.
2. pick-instance-type: A CLI tool that helps you pick a recommended instance type.

GetRecommendedInstanceType

GetRecommendedInstanceType takes in an AWS region and a list of EC2 instance types and returns the first instance type in the list that is available in all Availability Zones (AZs) in the given region. If there’s no instance available in all AZs, this function exits with an error.

Example usage:

aws.GetRecommendedInstanceType(t, "eu-west-1", []string{"t2.micro", "t3.micro"})
// As of July, 2020, returns "t2.micro"

aws.GetRecommendedInstanceType(t, "ap-northeast-2", []string{"t2.micro", "t3.micro"})
// As of July, 2020, returns "t3.micro"

pick-instance-type

pick-instance-type is a CLI tool that you can download from the Terratest releases page (click “Assets” under any release). It takes in an AWS region and a list of EC2 instance types and prints to stdout the first instance type in the list that is available in all Availability Zones (AZs) in the given region. If there’s no instance available in all AZs, pick-instance-type exits with an error.

Example usage:

# Data below is from July, 2020

$ pick-instance-type eu-west-1 t2.micro t3.micro
t2.micro

$ pick-instance-type ap-northeast-2 t2.micro t3.micro
t3.micro