Elastic IP addresses in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Elastic IP address behavior on instance stop and start

You have an EC2 instance with an Elastic IP (EIP) associated. What happens to the EIP when you stop and then start the instance?

A The Elastic IP is automatically disassociated and released when the instance stops.

B The Elastic IP is disassociated but not released; you must manually re-associate it after start.

C The Elastic IP remains associated with the instance after stop and start, preserving the public IP.

D The Elastic IP is released back to AWS and cannot be recovered after the instance stops.

💡 Hint

Think about how Elastic IPs are designed to provide a fixed public IP address.

Elastic IP addresses remain associated with the instance even if it is stopped and started. This allows the instance to keep the same public IP address.

❓ Architecture

intermediate

Using Elastic IPs for high availability

You want to design a highly available web service using two EC2 instances in different Availability Zones. How can Elastic IPs help in this design?

A Use a single Elastic IP and manually re-associate it to the healthy instance during failover.

B Assign an Elastic IP to each instance and use DNS failover to switch between them.

C Assign one Elastic IP to both instances simultaneously to share traffic.

D Elastic IPs cannot be used in high availability setups across Availability Zones.

💡 Hint

Consider how Elastic IPs can be moved between instances to maintain a fixed IP.

Elastic IPs can be reassigned from one instance to another in different Availability Zones to maintain a fixed IP during failover, enabling high availability.

❓ security

advanced

Security implications of Elastic IP address usage

Which of the following is a security best practice when using Elastic IP addresses in AWS?

A Regularly release unused Elastic IPs to avoid unnecessary charges and reduce attack surface.

B Assign Elastic IPs only to instances in private subnets to enhance security.

C Keep Elastic IPs allocated even when not in use to prevent others from using them.

D Use Elastic IPs to bypass security groups and network ACLs for easier access.

💡 Hint

Think about cost and security risks of unused public IPs.

Unused Elastic IPs incur charges and can increase the attack surface. Releasing them reduces costs and security risks.

❓ Configuration

advanced

Correct AWS CLI command to associate an Elastic IP

Which AWS CLI command correctly associates an Elastic IP address to an EC2 instance?

A aws ec2 associate-address --instance-id i-1234567890abcdef0 --allocation-id eipalloc-12345678 --public-ip 203.0.113.25

B aws ec2 associate-address --instance-id i-1234567890abcdef0 --public-ip 203.0.113.25

C aws ec2 associate-address --allocation-id eipalloc-12345678 --public-ip 203.0.113.25

D aws ec2 associate-address --instance-id i-1234567890abcdef0 --allocation-id eipalloc-12345678

💡 Hint

Check the required parameters for associating an Elastic IP to an instance.

The correct command uses the instance ID and the allocation ID of the Elastic IP to associate it.

✅ Best Practice

expert

Cost optimization with Elastic IP addresses

You have multiple Elastic IPs allocated but only some are associated with running instances. What is the best practice to optimize costs related to Elastic IPs?

A Keep all Elastic IPs allocated to avoid losing them, regardless of usage.

B Release Elastic IPs that are not associated with running instances to avoid hourly charges.

C Associate unused Elastic IPs to stopped instances to prevent charges.

D Convert Elastic IPs to standard public IPs to reduce costs.

💡 Hint

Consider AWS billing rules for Elastic IP addresses.

AWS charges for Elastic IPs that are allocated but not associated with a running instance. Releasing unused Elastic IPs avoids these charges.