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Elastic IP Addresses

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An Elastic IP address is a static, public IPv4 address that you can allocate to your AWS account and associate with an Amazon EC2 instance. Elastic IP addresses enable you to mask instance failures by remapping the address to another instance in your account. Unlike a regular public IP address, whi…

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AWS Certified Solutions Architect - Elastic IP Addresses Example Questions

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Question 1

You allocated an Elastic IP address for a new EC2 instance but have not yet associated it with the running instance. You notice an additional line item on your bill related to Elastic IP usage. What is the most likely reason for this charge?

Correct Answer: AWS charges for an Elastic IP address that is allocated but not associated with a running instance.

AWS Elastic IPs are free only when exactly one Elastic IP is associated with a running instance. Charges apply when an Elastic IP is allocated but not associated with a running instance, when it remains associated to a stopped instance, or when multiple Elastic IPs are associated with a single running instance. Simply routing traffic through an Elastic IP does not incur additional Elastic IP-specific charges beyond standard data transfer fees, and VPC configuration or promotions are not relevant to Elastic IP billing.

Question 2

During scheduled maintenance, you must stop and start an Amazon EC2 instance. For monitoring reasons, the instance must keep the same public IPv4 address after the stop/start cycle. In which scenario will the instance retain its public IP address?

Correct Answer: The instance has an Elastic IP associated with it

An Elastic IP address is a static public IPv4 address that you can allocate to your AWS account and associate with an EC2 instance or its primary ENI. Unlike the auto-assigned public IP in a VPC, which is released and replaced when an instance is stopped and started, an Elastic IP remains the same across stop/start cycles and even if you move it to another instance. Simply being in a VPC or using an ENI does not guarantee a static public IP. Auto Scaling groups can replace instances entirely, which changes any auto-assigned public IPs. Therefore, associating an Elastic IP is the only option listed that guarantees the instance retains the same public IP after a stop/start.

Question 3

You are the Solutions Architect managing an application hosted on EC2 instances. The team requires a new EC2 instance to be deployed and accessible even after stopping and starting the instance. What should you do?

Correct Answer: Associate an Elastic IP address to the EC2 instance.

Elastic IP addresses are static IPv4 addresses designed for dynamic cloud computing. Assigning an Elastic IP to an EC2 instance enables it to maintain the same public IP address even after stopping and starting the instance. The other options do not address the requirement of maintaining IP address persistence.

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