What should the solutions architect recommend?
Remove the two NAT instances and replace them with two NAT gateways in the same Availability Zone.
Use Auto Scaling groups with Network Load Balancers for the NAT instances in different Availability Zones.
Remove the two NAT instances and replace them with two NAT gateways in different Availability Zones.
Replace the two NAT instances with Spot Instances in different Availability Zones and deploy a Network Load Balancer.
Explanations:
NAT gateways should be deployed in different Availability Zones for high availability. Using two NAT gateways in the same AZ does not provide fault tolerance.
While using Auto Scaling groups with NLBs could help with scaling, NAT instances are not typically used in this manner and are less resilient compared to NAT gateways.
Replacing NAT instances with NAT gateways in different Availability Zones ensures high availability, fault tolerance, and automatic scaling capabilities to handle varying traffic loads.
Spot Instances may not provide the reliability needed for NAT functionality as they can be terminated at any time. Additionally, NAT gateways are preferred over NAT instances for this use case.
I rate that the answer is:
Remove the two NAT instances and replace them with two NAT gateways in different Availability Zones.