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Instance Metadata and User Data

5 minutes 5 Questions

Instance Metadata is data about an EC2 instance, such as instance type, instance ID, and more. User Data is custom data or scripts provided by the user during instance launch. Both Metadata and User Data can be used to configure and manage instances, including passing information between instances and triggering automation tasks. These can be accessed and used by applications running on the instance to make dynamic decisions or configure software at boot time.

Instance Metadata and User Data

What it is:
Instance Metadata is a data about your instance that you can use to configure or manage the running instance. User Data is arbitrary data that you can provide when you launch an instance, which can be used to perform common automated configuration tasks and even run scripts after the instance starts.

Why is it important:
Instance Metadata and User Data provide a way to supply instance-specific data at launch time. This helps in scripting automation and configuration tasks on the instances. It also allows you to manage your instances more efficiently.

How it Works:
Instance Metadata is accessible from within the instance itself. You can access it using simple HTTP tools or AWS SDKs that use HTTP requests. While User Data is information that you supply when you launch an instance. You can supply this data in the form of a script which will automatically run on instance startup.

Exam Tips: Answering Questions on Instance Metadata and User Data
Always keep in mind that Instance Metadata is data regarding the instance which can be accessed from within the instance itself. User Data, on the other hand, is provided by the user at the time of instance launch to automate the configuration of instances. Also, note that User Data scripts execute as the root user, but it's recommended to switch to a less privileged user to perform tasks. An understanding of these key aspects will be critical for answering questions effectively in the exam.

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Question 1

You are migrating your existing Ubuntu-based applications to AWS and launching them on EC2 instances. You need to set up a custom user data script when creating the instances. Where can you find the script after launching the instances?

Correct Answer: /var/lib/cloud/instances/instance-id/user-data.txt

On Ubuntu-based instances, the user data script can be found under '/var/lib/cloud/instances/instance-id/user-data.txt'. All other paths provided are either log files, unrelated to user data, or simply incorrect file paths.

Question 2

You want to run a startup script on your EC2 instance at launch by passing user data. In which format does the user data need to be?

Correct Answer: Shell script or cloud-init directive

User data should be in shell script or cloud-init directive format for it to be executed during the instance launch. Formats like JSON, YAML, XML, or plain text without valid script syntax will not work.

Question 3

You are debugging issues with user data on an Amazon Linux EC2 instance. Where can you find the log file containing the user data execution output?

Correct Answer: /var/log/cloud-init-output.log

On an Amazon Linux EC2 instance, the user data execution output is stored in the /var/log/cloud-init-output.log file. The other file paths provided are incorrect or unrelated to user data execution logs.

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