Learn how to establish centralized network firewall inspection across multiple VPCs using AWS Transit Gateway and Gateway Load Balancer endpoints.
Table of Contents
Question
A company’s existing AWS environment contains public application servers that run on Amazon EC2 instances. The application servers run in a VPC subnet. Each server is associated with an Elastic IP address.
The company has a new requirement for firewall inspection of all traffic from the internet before the traffic reaches any EC2 instances. A security engineer has deployed and configured a Gateway Load Balancer (GLB) in a standalone VPC with a fleet of third-party firewalls.
How should a network engineer update the environment to ensure that the traffic travels across the fleet of firewalls?
A. Deploy a transit gateway. Attach a GLB endpoint to the transit gateway. Attach the application VPC to the transit gateway. Update the application subnet route table’s default route destination to be the GLB endpoint. Ensure that the EC2 instances’ security group allows traffic from the GLB endpoint.
B. Update the application subnet route table to have a default route to the GLOn the standalone VPC that contains the firewall fleet, add a route in the route table for the application VPC’s CIDR block with the GLB endpoint as the destination. Update the EC2 instances’ security group to allow traffic from the GLB.
C. Provision a GLB endpoint in the application VPC in a new subnet. Create a gateway route table with a route that specifies the application subnet CIDR block as the destination and the GLB endpoint as the target. Associate the gateway route table with the internet gateway in the application VPUpdate the application subnet route table’s default route destination to be the GLB endpoint.
D. Instruct the security engineer to move the GLB into the application VPC. Create a gateway route table. Associate the gateway route table with the application subnet. Add a default route to the gateway route table with the GLB as its destination. Update the route table on the GLB to direct traffic from the internet gateway to the application servers. Ensure that the EC2 instances’ security group allows traffic from the GLB.
Answer
A. Deploy a transit gateway. Attach a GLB endpoint to the transit gateway. Attach the application VPC to the transit gateway. Update the application subnet route table’s default route destination to be the GLB endpoint. Ensure that the EC2 instances’ security group allows traffic from the GLB endpoint.
Explanation
The solution that will meet the requirements is A:
- Deploy a transit gateway and attach a GWLB endpoint to it
- Attach the application VPC to the transit gateway
- Update the application subnet route table’s default route to the GWLB endpoint
- Open security group ingress from the GWLB endpoint
This centralizes firewall inspection through the transit gateway and GWLB:
- Traffic naturally flows through GWLB before reaching instances
- No need to modify multiple route tables and security groups
The other options have flaws:
B – Does not centrally manage routing, requires multiple changes
C – Overly complex using VPC endpoints instead of transit gateway
D – Moving GWLB disrupts existing architecture design
Centralizing routing through a transit gateway with the GWLB endpoint provides the simplest management of inspection without affecting the existing environment design.
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