Legacy Application Failover Mechanisms

Answer - B and D.

Option A is incorrect because rerouting to a failover instance cannot be done through a Traffic Manager.

Option B is CORRECT because the attributes of a network interface follow it as it's attached or detached from an instance and reattached to another instance.

When you move a network interface from one instance to another, network traffic is redirected to the new instance.

Option C is incorrect because Route 53 cannot reroute the traffic to the failover instance with the same IP address.

Option D is CORRECT because you can have a secondary IP address that can be configured on the primary ENI of the failover instance.

Best Practices for Configuring Network Interfaces.

You can attach a network interface to an instance when it's running (hot attach), when it's stopped (warm attach), or when the instance is being launched (cold attach).

You can detach secondary (ethN) network interfaces when the instance is running or stopped.

However, you can't detach the primary (eth0) interface.

You can attach a network interface in one subnet to an instance in another subnet in the same VPC; however, both the network interface and the instance must reside in the same Availability Zone.

When launching an instance from the CLI or API, you can specify the network interfaces to attach to the instance for both the primary (eth0) and additional network interfaces.

Launching an Amazon Linux or Windows Server instance with multiple network interfaces automatically configures interfaces, private IPv4 addresses, and route tables on the operating system of the instance.

A warm or hot attach of an additional network interface may require you to manually bring up the second interface, configure the private IPv4 address, and modify the route table accordingly.

Instances running Amazon Linux or Windows Server automatically recognize the warm or hot attach and configure themselves.

Attaching another network interface to an instance (for example, a NIC teaming configuration) cannot be used as a method to increase or double the network bandwidth to or from the dual-homed instance.

If you attach two or more network interfaces from the same subnet to an instance, you may encounter networking issues such as asymmetric routing.

If possible, use a secondary private IPv4 address on the primary network interface instead.

For more information, see Assigning a Secondary Private IPv4 Address.

For more information on Network Interfaces, please visit the below URL-

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-eni.html

The best answer for this scenario would be option B, which suggests creating a secondary Elastic Network Interface (ENI) that can be moved to the failover instance.

Explanation: When managing a legacy application inside a Virtual Private Cloud (VPC) with hard-coded IP addresses in its configuration, the goal is to provide high availability without changing the existing configuration. To achieve this, the failover mechanism should involve minimal reconfiguration.

Option A, which suggests using a traffic manager, may not be suitable in this case as it would require changing the configuration to include the traffic manager's endpoint. Additionally, if the application has hard-coded IP addresses, it may not be possible to change the configuration easily.

Option C, which suggests using Route53 health checks, can help reroute the traffic to the failover instance in case of a failure. However, it requires changing the DNS configuration, which may not be possible in a legacy application with hard-coded IP addresses.

Option D, which suggests assigning a secondary private IP address to the primary ENI of the failover instance, may not be the best solution as it still requires changing the configuration to include the secondary IP address.

Therefore, option B is the best choice as it involves creating a secondary ENI that can be moved to the failover instance. This allows the failover instance to have the same IP address as the primary instance, which means that the application can continue to operate without any reconfiguration. In case of a failure, the secondary ENI can be moved to the failover instance, and the traffic will automatically start flowing to the failover instance, ensuring high availability without any significant changes to the existing configuration.