CLI scripting basics in AWS - Mini Project: Build & Apply

CLI scripting basics

📖 Scenario: You are managing a small cloud environment on AWS. You want to automate the process of listing your EC2 instances and filtering them by a specific tag using AWS CLI commands in a script.

🎯 Goal: Create a simple AWS CLI script that lists all EC2 instances, filters them by a tag named Environment with the value Development, and outputs the instance IDs.

📋 What You'll Learn

Use AWS CLI commands to list EC2 instances

Filter instances by the tag Environment with value Development

Extract and output only the instance IDs

💡 Why This Matters

🌍 Real World

Automating AWS resource management using CLI scripts saves time and reduces errors in cloud operations.

💼 Career

Cloud engineers and DevOps professionals often write CLI scripts to manage and automate cloud infrastructure efficiently.

1

Create a variable with the AWS CLI command to list all EC2 instances

Create a variable called list_instances_cmd and assign it the AWS CLI command string aws ec2 describe-instances.

AWS

# Create a variable called list_instances_cmd with the command string
# Your code here

Hint

Assign the exact string aws ec2 describe-instances to the variable list_instances_cmd.

2

Add a filter variable for the tag Environment=Development

Create a variable called filter_tag and assign it the AWS CLI filter string --filters Name=tag:Environment,Values=Development.

AWS

list_instances_cmd = "aws ec2 describe-instances"
# Create a variable called filter_tag with the filter string
# Your code here

Hint

Use the exact filter string with --filters Name=tag:Environment,Values=Development.

3

Combine the command and filter to list filtered instances

Create a variable called filtered_cmd that combines list_instances_cmd and filter_tag separated by a space.

AWS

list_instances_cmd = "aws ec2 describe-instances"
filter_tag = "--filters Name=tag:Environment,Values=Development"
# Combine list_instances_cmd and filter_tag into filtered_cmd
# Your code here

Hint

Join the two strings with a space between them.

4

Add the query to output only instance IDs

Update the variable final_cmd by adding the query option --query 'Reservations[].Instances[].InstanceId' --output text to filtered_cmd separated by a space.

AWS

list_instances_cmd = "aws ec2 describe-instances"
filter_tag = "--filters Name=tag:Environment,Values=Development"
filtered_cmd = list_instances_cmd + " " + filter_tag
# Add query and output options to filtered_cmd and assign to final_cmd
# Your code here

Hint

Append the exact query and output options to the filtered command string.

Practice

1. What does the AWS CLI command aws s3 ls do?

easy

A. Deletes all S3 buckets in your AWS account

B. Creates a new S3 bucket

C. Lists all S3 buckets in your AWS account

D. Uploads a file to an S3 bucket

Solution

1. Step 1: Understand the command structure

   The command uses aws s3 which relates to the S3 service, and ls which means list.

2. Step 2: Interpret the command action

   Listing in S3 context means showing all buckets or objects. Without extra parameters, it lists all buckets.

3. Final Answer:

   Lists all S3 buckets in your AWS account -> Option C

4. Quick Check:

   Command aws s3 ls lists buckets [OK]

Hint: Remember: 'ls' means list, so it shows existing resources [OK]

Common Mistakes:

• Confusing 'ls' with 'rm' (delete)
• Thinking it creates resources
• Assuming it uploads files

2. Which of the following is the correct syntax to create an EC2 instance using AWS CLI?

easy

A. aws ec2 run-instances --image-id ami-12345678 --count 1

B. aws ec2 create-instance --image-id ami-12345678 --count 1

C. aws ec2 start-instance --image-id ami-12345678 --count 1

D. aws ec2 launch-instance --image-id ami-12345678 --count 1

Solution

1. Step 1: Identify the correct AWS CLI command for EC2 instance creation

   The official command to create EC2 instances is run-instances.

2. Step 2: Check the syntax correctness

   aws ec2 run-instances --image-id ami-12345678 --count 1 uses aws ec2 run-instances --image-id ami-12345678 --count 1, which is the correct syntax to launch one instance.

3. Final Answer:

   aws ec2 run-instances --image-id ami-12345678 --count 1 -> Option A

4. Quick Check:

   EC2 instance creation uses 'run-instances' command [OK]

Hint: Use 'run-instances' to launch EC2, not 'create-instance' [OK]

Common Mistakes:

• Using 'create-instance' which is invalid
• Confusing 'start-instance' with creation
• Using 'launch-instance' which is not a valid command

3. What will be the output of this AWS CLI command?

aws s3api list-buckets --query 'Buckets[].Name' --output json

medium

A. A JSON array of bucket names

B. A list of bucket creation dates

C. An error because of wrong syntax

D. A plain text list of bucket names

Solution

1. Step 1: Understand the command components

   The command uses list-buckets to get all buckets, with a query to extract only the bucket names.

2. Step 2: Analyze the output format

   The --output json option formats the result as JSON, so the output is a JSON array of bucket names.

3. Final Answer:

   A JSON array of bucket names -> Option A

4. Quick Check:

   Query filters names, output json formats as JSON array [OK]

Hint: Query filters data, output json formats it as JSON [OK]

Common Mistakes:

• Expecting plain text instead of JSON
• Confusing bucket names with creation dates
• Assuming syntax error due to query

4. You run this command to delete an S3 bucket:

aws s3 rb s3://my-bucket

But it fails with an error. What is the most likely cause?

medium

A. You need to use aws s3 rm instead

B. The bucket is not empty

C. The bucket name is invalid

D. The AWS CLI is not installed

Solution

1. Step 1: Understand the command purpose

   aws s3 rb removes (deletes) an S3 bucket, but only if it is empty.

2. Step 2: Identify the common error cause

   If the bucket contains files, the command fails. You must delete all objects first.

3. Final Answer:

   The bucket is not empty -> Option B

4. Quick Check:

   Bucket must be empty before removal [OK]

Hint: Empty bucket before deleting with 'rb' command [OK]

Common Mistakes:

• Trying to delete non-empty bucket directly
• Confusing 'rm' (remove objects) with 'rb' (remove bucket)
• Assuming AWS CLI is not installed without checking

5. You want to write a script that lists all EC2 instances and then stops each one. Which AWS CLI commands should you combine in the script?

hard

A. Use aws ec2 show-instances to list, then aws ec2 power-off-instances to stop

B. Use aws ec2 list-instances to list, then aws ec2 terminate-instances to stop

C. Use aws ec2 get-instances to list, then aws ec2 shutdown-instances to stop

D. Use aws ec2 describe-instances to list, then aws ec2 stop-instances --instance-ids to stop

Solution

1. Step 1: Identify the correct command to list EC2 instances

   The correct command to list instances is describe-instances.

2. Step 2: Identify the correct command to stop instances

   To stop instances, use stop-instances with the instance IDs.

3. Step 3: Combine commands in script logic

   First list instances to get IDs, then stop them using those IDs.

4. Final Answer:

   Use aws ec2 describe-instances to list, then aws ec2 stop-instances --instance-ids to stop -> Option D

5. Quick Check:

   List with describe, stop with stop-instances [OK]

Hint: List with 'describe-instances', stop with 'stop-instances' [OK]

Common Mistakes:

• Using non-existent commands like 'list-instances'
• Confusing 'terminate' with 'stop' (termination deletes)
• Using wrong commands that cause errors