Specifying User Data for EC2

In this lesson, we will learn about a very useful feature called EC2 user data. Looking at the name, it isn’t immediately obvious what it does, so let’s look into it: “When you launch an instance in Amazon EC2, you have the option of passing user data to the instance that can be used to perform common automated configuration tasks and even run scripts after the instance starts.” $^7$

This means that EC2 user data is a script that runs on the first boot of an instance. It’s important to remember that it only runs once. If we start and stop the instance, it will not run again.

AWS supports two formats for this script—a standard shell script and a cloud-init file. a cloud-init file is a configuration file specifically used for cloud providers. AWS uses them to set up our SSH keys within the instance. In this lesson, we’ll learn to use shell scripts with EC2 user data.

This script will be executed as the root user, so it has full access to the system.

But what would we use this for?

We can use the EC2 user data script for almost anything, like:

• Installing a software
• Updating a software
• Starting services
• Changing configuration
• Running tests

However, as a general rule, we should only run things in the EC2 user data script that we cannot add to the underlying AMI ...