Root user vs IAM user in AWS - Performance Comparison

Time Complexity: Root user vs IAM user

O(n)

Understanding Time Complexity

We want to understand how the number of operations changes when using a root user versus an IAM user in AWS.

Specifically, how does the choice affect the number of permission checks and API calls?

Scenario Under Consideration

Analyze the time complexity of permission checks when a user performs actions.

# Root user performs an action
aws s3 ls

# IAM user performs the same action
aws s3 ls --profile iam-user
    

This sequence shows a root user and an IAM user listing S3 buckets, triggering permission checks.

Identify Repeating Operations

Look at the permission checks and API calls involved.

• Primary operation: Permission check before each API call.
• How many times: Once per API call, repeated for each action.

How Execution Grows With Input

As the number of actions grows, permission checks happen for each.

Input Size (n)	Approx. Permission Checks
10	10
100	100
1000	1000

Pattern observation: Permission checks grow linearly with the number of actions.

Final Time Complexity

Time Complexity: O(n)

This means the number of permission checks grows directly with the number of actions performed.

Common Mistake

[X] Wrong: "Root user skips permission checks, so it is faster for many actions."

[OK] Correct: Root user still triggers permission checks internally; the difference is in permission scope, not number of checks.

Interview Connect

Understanding how permission checks scale helps you design secure and efficient AWS environments, a key skill in cloud roles.

Self-Check

"What if we added permission caching for IAM users? How would the time complexity change?"

Practice

1. Which AWS user has full access to all resources and billing information by default?

easy

A. IAM user with admin permissions

B. Federated user

C. IAM user with read-only permissions

D. Root user

Solution

1. Step 1: Understand AWS user types

   The root user is the original account owner with full control over all AWS services and billing.

2. Step 2: Compare with IAM users

   IAM users have permissions assigned and do not have full access by default.

3. Final Answer:

   Root user -> Option D

4. Quick Check:

   Full access = Root user [OK]

Hint: Root user = full control, IAM users = limited [OK]

Common Mistakes:

• Confusing IAM admin user with root user
• Thinking IAM users have full billing access by default
• Assuming federated users have root privileges

2. Which of the following is the correct way to create an IAM user in AWS Management Console?

easy

A. Use AWS Billing dashboard to add a user

B. Go to IAM > Users > Add user, then set permissions

C. Log in as root user and create a new AWS account

D. Create a new user under AWS Organizations

Solution

1. Step 1: Locate IAM user creation

   IAM users are created in the IAM service under Users > Add user.

2. Step 2: Understand permissions assignment

   After adding a user, you assign permissions directly or via groups.

3. Final Answer:

   Go to IAM > Users > Add user, then set permissions -> Option B

4. Quick Check:

   IAM user creation = IAM console [OK]

Hint: Create IAM users only in IAM console, not billing or orgs [OK]

Common Mistakes:

• Trying to create IAM users in Billing dashboard
• Confusing AWS Organizations with IAM user creation
• Creating new AWS accounts instead of IAM users

3. If an IAM user tries to delete an S3 bucket but gets an Access Denied error, what is the most likely reason?

medium

A. The IAM user does not have delete permissions for the bucket

B. The root user disabled S3 service

C. The bucket is owned by another AWS account

D. IAM users cannot delete S3 buckets

Solution

1. Step 1: Check IAM user permissions

   IAM users need explicit permissions to delete S3 buckets; lacking these causes Access Denied.

2. Step 2: Evaluate other options

   Root user cannot disable S3 service; buckets owned by others can cause issues but usually different errors; IAM users can delete buckets if permitted.

3. Final Answer:

   The IAM user does not have delete permissions for the bucket -> Option A

4. Quick Check:

   Access Denied = missing permissions [OK]

Hint: Access Denied usually means missing permission, not service disabled [OK]

Common Mistakes:

• Assuming root user disables services
• Believing IAM users cannot delete buckets at all
• Ignoring bucket ownership issues

4. An administrator accidentally used the root user credentials for daily tasks and now wants to improve security. What should they do to fix this?

medium

A. Create IAM users with appropriate permissions and avoid using root user for daily tasks

B. Delete the root user and use only IAM users

C. Share root user credentials with team members for convenience

D. Disable MFA on root user to simplify login

Solution

1. Step 1: Understand root user best practices

   Root user should be used only for account setup and billing, not daily tasks.

2. Step 2: Implement IAM users for daily work

   Create IAM users with limited permissions for daily tasks to improve security.

3. Final Answer:

   Create IAM users with appropriate permissions and avoid using root user for daily tasks -> Option A

4. Quick Check:

   Use IAM users daily, root only for emergencies [OK]

Hint: Use IAM users daily; keep root user locked down [OK]

Common Mistakes:

• Trying to delete root user (impossible)
• Sharing root credentials widely
• Disabling MFA on root user

5. A company wants to restrict billing access to only the root user but allow IAM users to manage resources. Which AWS best practice should they follow?

hard

A. Create IAM users with billing permissions and avoid using root user

B. Grant all IAM users full admin access including billing

C. Use the root user only for billing and create IAM users with resource permissions

D. Disable root user and use IAM users for all tasks

Solution

1. Step 1: Understand billing access control

   Billing access is sensitive and should be limited to the root user for security.

2. Step 2: Assign resource management to IAM users

   IAM users should have permissions to manage resources but not billing.

3. Final Answer:

   Use the root user only for billing and create IAM users with resource permissions -> Option C

4. Quick Check:

   Billing = root only; resource management = IAM users [OK]

Hint: Keep billing to root user; IAM users manage resources [OK]

Common Mistakes:

• Giving IAM users billing permissions unnecessarily
• Disabling root user (not possible)
• Granting full admin to all IAM users