Which solution will meet these requirements?
Deploy three NAT gateways, one in each public subnet. Assign the Elastic IP address to the NAT gateways. Turn on health checks for the NAT gateways. If a NAT gateway fails a health check, recreate the NAT gateway and assign the Elastic IP address to the new NAT gateway.
Replace the ALB with a Network Load Balancer (NLB). Assign the Elastic IP address to the NLTurn on health checks for the NLIn the case of a failed health check, redeploy the NLB in different subnets.
Deploy a single NAT gateway in a public subnet. Assign the Elastic IP address to the NAT gateway. Use Amazon CloudWatch with a custom metric to monitor the NAT gateway. If the NAT gateway is unhealthy, invoke an AWS Lambda function to create a new NAT gateway in a different subnet. Assign the Elastic IP address to the new NAT gateway.
Assign the Elastic IP address to the ALB. Create an Amazon Route 53 simple record with the Elastic IP address as the value. Create a Route 53 health check. In the case of a failed health check, recreate the ALB in different subnets.
Explanations:
Deploying three NAT gateways would not be necessary as it would not provide high availability; if one NAT gateway fails, recreating it would not guarantee a seamless communication. AWS best practices recommend using a single NAT gateway in a public subnet for this type of use case. Health checks cannot be configured for NAT gateways; they are inherently managed by AWS.
Replacing the ALB with a Network Load Balancer (NLB) is not required because the ALB is already functioning correctly for the application’s needs. Furthermore, NLBs do not support health checks in the same way ALBs do, and recreating an NLB in different subnets would not address the issue of maintaining a persistent connection with the on-premises systems.
Deploying a single NAT gateway in a public subnet and assigning the Elastic IP address to it is a valid approach. This solution allows outbound internet access for the EC2 instances. Using CloudWatch to monitor the NAT gateway and invoking a Lambda function to recreate the NAT gateway in case of failure ensures high availability and automatic failover. This approach aligns with best practices for maintaining connectivity to on-premises systems.
Assigning the Elastic IP to the ALB is not suitable since the ALB is designed for routing traffic, not for maintaining outbound connections to on-premises systems. Additionally, recreating the ALB in different subnets based on health checks does not address the requirement for persistent communication with on-premises systems and may introduce additional complexity without solving the core connectivity issue.
I deduce that the answer is:
Deploy a single NAT gateway in a public subnet. Assign the Elastic IP address to the NAT gateway. Use Amazon CloudWatch with a custom metric to monitor the NAT gateway. If the NAT gateway is unhealthy, invoke an AWS Lambda function to create a new NAT gateway in a different subnet. Assign the Elastic IP address to the new NAT gateway.