Strategies for Smooth Application Switchover on Failure

Correct Answer: B.

The AWS Documentation mentions the following.

You can disassociate an Elastic IP address from a resource, and reassociate it with a different resource.

Any open connections to an instance continue to work for a time even after you disassociate its Elastic IP address and reassociate it with another instance.

We recommend that you reopen these connections using the reassociated Elastic IP address.

Option A is incorrect since the ENI would not help since the IP addressing is different for secondary ENI's.

Option C is incorrect since the Internet gateway is already a durable and highly available software.

Option D is incorrect since there is no mention of traffic needing to pass through the Internet from a private subnet.

For more information on Elastic IP addressing, please refer to the below URL-

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/elastic-ip-addresses-eip.html

In order to ensure a smooth switchover of the application onto a new instance if the primary one fails, there are several options that can be considered:

A. Assign a secondary ENI to the primary instance: An Elastic Network Interface (ENI) is a virtual network interface that can be attached to an EC2 instance. Assigning a secondary ENI to the primary instance can help ensure a smooth switchover in the event of a failure by providing a backup interface that can be used to re-route traffic to a secondary instance. This option can be particularly useful in scenarios where the primary instance has multiple network interfaces, such as instances in a cluster or a high availability configuration.

B. Assign an Elastic IP to the primary instance: An Elastic IP is a static, public IP address that can be associated with an EC2 instance. Assigning an Elastic IP to the primary instance can help ensure a smooth switchover by allowing the secondary instance to quickly assume the IP address of the failed primary instance. This can be particularly useful in scenarios where external clients or applications are dependent on the IP address of the primary instance.

C. Create a secondary Internet gateway for the VPC: An Internet gateway is a horizontally scaled, redundant, and highly available VPC component that allows communication between instances in your VPC and the internet. Creating a secondary Internet gateway for the VPC can help ensure a smooth switchover in the event of a failure by providing a backup gateway that can be used to re-route traffic to a secondary instance. This option can be particularly useful in scenarios where the primary instance is dependent on an external network connection or service.

D. Create a secondary NAT gateway for the VPC: A NAT gateway is a managed, highly available NAT service that allows instances in a private subnet to connect to the internet or other AWS services, but prevents the internet from initiating connections back to the instances. Creating a secondary NAT gateway for the VPC can help ensure a smooth switchover in the event of a failure by providing a backup gateway that can be used to re-route traffic to a secondary instance. This option can be particularly useful in scenarios where the primary instance is located in a private subnet and requires internet access.

Out of these options, assigning an Elastic IP to the primary instance (option B) is the most suitable option for ensuring a smooth switchover of the application onto a new instance if the primary one fails, as it allows the secondary instance to quickly assume the IP address of the failed primary instance. However, it's important to note that other options can also be useful depending on the specific requirements of the application and its infrastructure.