Which solution will meet these requirements?
Update the Auto Scaling group to use the AZ2 subnet only. Delete and re-create the AZ1 subnet using half the previous address space. Adjust the Auto Scaling group to also use the new AZ1 subnet. When the instances are healthy, adjust the Auto Scaling group to use the AZ1 subnet only. Remove the current AZ2 subnet. Create a new AZ2 subnet using the second half of the address space from the original AZ1 subnet. Create a new AZ3 subnet using half the original AZ2 subnet address space, then update the Auto Scaling group to target all three new subnets.
Terminate the EC2 instances in the AZ1 subnet. Delete and re-create the AZ1 subnet using half the address space. Update the Auto Scaling group to use this new subnet. Repeat this for the second AZ. Define a new subnet in AZ3, then update the Auto Scaling group to target all three new subnets.
Create a new VPC with the same IPv4 address space and define three subnets, with one for each AZ. Update the existing Auto Scaling group to target the new subnets in the new VPC.
Update the Auto Scaling group to use the AZ2 subnet only. Update the AZ1 subnet to have half the previous address space. Adjust the Auto Scaling group to also use the AZ1 subnet again. When the instances are healthy, adjust the Auto Scaling group to use the AZ1 subnet only. Update the current AZ2 subnet and assign the second half of the address space from the original AZ1 subnet. Create a new AZ3 subnet using half the original AZ2 subnet address space, then update the Auto Scaling group to target all three new subnets.
Explanations:
This option ensures connectivity is maintained and does not require additional IPv4 space. It strategically reconfigures each subnet in steps: reallocating half the address space from each original subnet to create new, smaller subnets across all three AZs. This approach allows the Auto Scaling group to expand to the new AZ3 without downtime or connectivity disruption.
Terminating EC2 instances in AZ1 would cause potential service downtime, which contradicts the requirement. Additionally, deleting subnets and recreating them without maintaining a transition period risks interrupting connectivity, making this option unsuitable for a high-availability, continuous-uptime environment.
Creating a new VPC with the same IPv4 range is not feasible, as duplicate CIDR blocks across VPCs would conflict, especially with an on-premises connection. Additionally, migrating instances to a new VPC would likely cause downtime, violating the requirement for uninterrupted connectivity.
This option incorrectly suggests reducing the size of the AZ1 subnet and then reallocating address space without a phased transition. This would likely disrupt service due to connectivity issues and risks IP conflicts without careful address management. The proposed steps would also potentially cause downtime, failing to meet the requirements.
I surmise that the answer is:
Update the Auto Scaling group to use the AZ2 subnet only. Delete and re-create the AZ1 subnet using half the previous address space. Adjust the Auto Scaling group to also use the new AZ1 subnet. When the instances are healthy, adjust the Auto Scaling group to use the AZ1 subnet only. Remove the current AZ2 subnet. Create a new AZ2 subnet using the second half of the address space from the original AZ1 subnet. Create a new AZ3 subnet using half the original AZ2 subnet address space, then update the Auto Scaling group to target all three new subnets.