How should a solutions architect ensure that the web application can continue to call the third-party API after the migration?
Associate a block of customer-owned public IP addresses to the VPC. Enable public IP addressing for public subnets in the VPC.
Register a block of customer-owned public IP addresses in the AWS account. Create Elastic IP addresses from the address block and assign them to the NAT gateways in the VPC.
Create Elastic IP addresses from the block of customer-owned IP addresses. Assign the static Elastic IP addresses to the ALB.
Register a block of customer-owned public IP addresses in the AWS account. Set up AWS Global Accelerator to use Elastic IP addresses from the address block. Set the ALB as the accelerator endpoint.
Explanations:
Associating a block of public IP addresses to the VPC and enabling public IP addressing for public subnets does not solve the issue because the EC2 instances in the private subnet need to access the third-party API. Public IPs on subnets won’t route traffic correctly from private instances.
Registering a block of customer-owned public IP addresses and creating Elastic IP addresses from that block to assign to the NAT gateways allows outbound traffic from the private subnet through the NAT gateways, which then uses the public IPs to reach the third-party API. This meets the requirement for the third-party allow list.
Assigning Elastic IP addresses to the ALB does not help with the private EC2 instances accessing the third-party API since the ALB is not involved in the API calls and does not manage outbound traffic from private subnets. The instances still need a route through the NAT gateway for outbound requests.
While AWS Global Accelerator can help manage and optimize traffic, it does not solve the issue of ensuring that the private EC2 instances can access the third-party API. The Elastic IP addresses need to be assigned to the NAT gateways, not the Global Accelerator.