:

This solution meets all requirements for high availability, multi-region connectivity, and encrypted access to both private (VPC) and public (Amazon S3) resources.

Option B addresses the high availability requirement by establishing redundant AWS Direct Connect (DX) connections, one from each of the two on-premises data centers. This eliminates the DX connection as a single point of failure.

Option D correctly configures the logical connectivity. A public virtual interface (VIF) is required to access public AWS service endpoints like Amazon S3 over a DX connection. To meet the encryption requirement for traffic to the VPCs, an AWS Site-to-Site VPN is established over the public VIF. This creates an encrypted tunnel from the on-premises data centers to the Virtual Private Gateways (VGWs) or Transit Gateways (TGWs) in the AWS Regions.

A. A private VIF is used to access private IP addresses within a VPC and cannot be used to directly access public AWS service endpoints like Amazon S3.

C. A single Direct Connect connection from only one data center does not satisfy the high availability requirement, as it creates a single point of failure.

E. A transit VIF is used exclusively to connect a Direct Connect Gateway to a Transit Gateway for VPC access; it cannot be used to access public services like Amazon S3.

1. AWS Direct Connect User Guide, Resiliency Recommendations: "For critical workloads, we recommend that you have connections at more than one location. [...] You can achieve high availability by using separate connections that terminate on separate devices in more than one location." This supports establishing a DX connection from each data center (Option B).

2. AWS Direct Connect User Guide, Virtual interface types: "Public virtual interface: Access all AWS public services using public IP addresses." This documentation confirms that a public VIF is the correct choice for accessing Amazon S3 (supporting Option D).

3. AWS Direct Connect User Guide, AWS Direct Connect and VPN: "You can configure an AWS Site-to-Site VPN connection to use a public virtual interface to establish a secure, private session. This combination offers the benefits of a connection with higher bandwidth and a more consistent network experience than an internet-based VPN connection." This directly validates the pattern of using a Site-to-Site VPN over a public VIF for encrypted communication (supporting Option D).

4. AWS Direct Connect User Guide, Direct Connect gateways: "You can use a Direct Connect gateway to connect your AWS Direct Connect connection over a private virtual interface to one or more VPCs in your account that are located in the same or different Regions." While not an answer choice, this concept is relevant to how the multi-region VPC access would be implemented underneath the VPN layer. The VPN itself can terminate in any region over the public VIF.

This solution provides the most scalable, secure, and operationally efficient architecture for a SaaS provider. AWS PrivateLink is purpose-built for this use case, allowing hundreds of AWS customers to connect to the SaaS application privately and securely from their own VPCs. It creates a private endpoint in the customer's VPC, eliminating the need for VPC peering, internet gateways, or complex routing tables. This directly solves the stated problem of managing complex routing and NAT. For on-premises customers, terminating IPsec VPN connections is the required method, and using a routing appliance or an AWS Transit Gateway/Virtual Private Gateway are all viable ways to achieve this.

A. While Transit Gateway can connect hundreds of VPCs and VPNs, it is less ideal than PrivateLink for this SaaS use case as it still requires the provider to manage routing and segmentation between all connected customers.

C. VPC peering is not a scalable solution for "hundreds of customers" due to hard limits on the number of peering connections per VPC and the operational complexity of managing CIDR conflicts and individual connections.

D. Using Site-to-Site VPN for connectivity between customer VPCs and the SaaS VPC is inefficient, adds unnecessary encryption overhead, and complicates network management compared to native AWS private connectivity options.

1. AWS PrivateLink Developer Guide, "What is AWS PrivateLink?": The documentation states, "You can make your service, hosted in your own Amazon VPC, available to other AWS customers... This is referred to as an endpoint service... Your service consumers can create a connection from their VPC to your endpoint service... using an interface VPC endpoint." This describes the exact pattern for the SaaS provider and its AWS customers.

2. AWS Whitepaper, "SaaS Lens - AWS Well-Architected Framework", Page 21: Under the "Networking and Connectivity" section, the whitepaper recommends, "AWS PrivateLink is a highly secure and scalable technology that enables you to privately expose your SaaS service to customers on the AWS network... This approach simplifies the network architecture for your customers, and removes the need for an Internet Gateway, NAT devices, or firewall rules to allow traffic from the customer VPC." This directly supports the choice of PrivateLink to solve the scenario's challenges.

3. Amazon VPC User Guide, "VPC peering basics and limitations": The guide notes, "A VPC has a limit on the number of active and pending VPC peering connections that it can have." The default limit is 50, and the maximum is 125, which makes peering unsuitable for "hundreds of customers."

4. AWS Documentation, "Transit Gateway use cases": Transit Gateway is described as a "network transit hub" to interconnect VPCs and on-premises networks. While powerful, it is a general-purpose networking tool. For the specific SaaS provider-to-consumer model, PrivateLink offers superior isolation and operational simplicity by abstracting the network layer entirely.

Amazon VPC IP Address Manager (IPAM) is a managed service specifically designed to plan, track, and monitor IP addresses for AWS workloads. By creating pools in IPAM and enabling auto-import, IPAM automatically discovers and tracks the IP address usage of existing VPCs and subnets. IPAM natively publishes utilization metrics to Amazon CloudWatch. Configuring a CloudWatch alarm on the IPAM pool's utilization metric is the most direct and efficient method to trigger an Amazon Simple Notification Service (Amazon SNS) notification when a specific threshold is breached. This approach provides a fully managed monitoring and alerting solution, fulfilling the requirements with the least operational overhead.

B. This solution requires developing, deploying, and maintaining a custom AWS Lambda function and associated logging/metric filtering, which creates significantly more operational overhead than using the purpose-built IPAM service.

C. Similar to option B, this approach relies on a custom Lambda function. While publishing custom metrics is more direct than logging, it still constitutes a custom-built solution with higher operational overhead than the managed IPAM service.

D. While IPAM is the correct service, Amazon EventBridge is primarily for event-driven architectures that react to state changes (e.g., a pool's state changes to 'depleted'). For continuous monitoring against a specific numeric threshold, Amazon CloudWatch alarms are the more appropriate and direct tool.

1. AWS Documentation, VPC IP Address Manager (IPAM) User Guide, "Monitor IP address usage with IPAM": "VPC IPAM makes it easier for you to monitor IP address usage throughout your network and provides alerts when there is a potential for IP address exhaustion." This confirms IPAM is the purpose-built service for the scenario.

2. AWS Documentation, VPC IP Address Manager (IPAM) User Guide, "Monitor IPAM metrics using CloudWatch": This section details the metrics that IPAM sends to CloudWatch, including IpamPoolAllocation, which represents the percentage of the pool's address space that is allocated. It explicitly states, "You can use these metrics to set up alarms that notify you when you're close to exhausting the address space in a pool." This directly supports the solution in option A.

3. AWS Documentation, Amazon CloudWatch User Guide, "Using Amazon CloudWatch alarms": "You can create a CloudWatch alarm that watches a single CloudWatch metric... If the metric breaches the threshold for a specified number of evaluation periods, the alarm performs one or more actions," such as sending a notification to an SNS topic. This confirms the mechanism described in option A is the standard and intended method for threshold-based alerting.

4. AWS Well-Architected Framework, "Operational Excellence Pillar" (Whitepaper), Design Principle OPS 8: "Use managed services to reduce the operational burden of managing physical or virtual servers." This principle supports choosing a managed service like IPAM over a custom solution involving Lambda functions (as in options B and C) to minimize operational overhead.

The question requires improving the network performance of a security appliance running on a single Amazon EC2 instance. The most direct methods to enhance an EC2 instance's network capabilities are by selecting an instance type with better underlying hardware features and by scaling it vertically.

Using an EC2 instance that supports enhanced networking (SR-IOV) provides significantly higher packets per second (PPS), lower inter-instance latency, and less network jitter. Increasing the EC2 instance size directly correlates to higher available network bandwidth. Larger instance types are allocated a greater share of network capacity, which is crucial for a device acting as a network chokepoint for all outbound traffic.

B. Send outbound traffic through a transit gateway.

A transit gateway is a network transit hub for interconnecting VPCs and on-premises networks. It simplifies routing but does not inherently increase the network performance of the EC2 security appliance itself.

D. Place the EC2 instance in a placement group within the VPC.

Placement groups optimize network performance between instances within the group. This does not improve performance for traffic flowing from the instance to an external location like an on-premises data center.

E. Attach multiple elastic network interfaces to the EC2 instance.

The total network bandwidth for an EC2 instance is determined by its type, not the number of network interfaces. Multiple ENIs do not increase the aggregate throughput of the instance.

1. Amazon EC2 Documentation - Enhanced networking on Linux: "Enhanced networking uses single root I/O virtualization (SR-IOV) to provide high-performance networking capabilities on supported instance types. SR-IOV is a method of device virtualization that provides higher I/O performance and lower CPU utilization when compared to traditional virtualized network interfaces." (Source: AWS Documentation, Enhanced networking on Linux, Section: "Enhanced networking").

2. Amazon EC2 Documentation - Amazon EC2 instance types: The instance type specifications clearly show that network bandwidth scales with instance size. For example, for M5 instances, m5.large has "Up to 10 Gbps" while m5.24xlarge has "100 Gbps". This demonstrates the direct relationship between instance size and network performance. (Source: AWS Documentation, Amazon EC2 Instance Types, Section: "General Purpose").

3. Amazon EC2 Documentation - Placement groups: "A cluster placement group is a logical grouping of instances within a single Availability Zone. ... A cluster placement group is recommended for applications that benefit from low network latency, high network throughput, or both, and if the majority of the network traffic is between the instances in the group." (Source: AWS Documentation, Placement groups, Section: "Cluster placement groups").

The most efficient solution with minimal changes is to establish a Transit Gateway (TGW) peering connection. TGW peering is a feature designed specifically to connect two Transit Gateways, enabling routing between their respective networks. Since both the company's TGW (TGW-C) and the partner's TGW (TGW-P) are in the same AWS Region (us-east-1), an intra-region peering attachment can be created. This approach allows both organizations to maintain their independent network architectures and routing domains while enabling secure, high-bandwidth connectivity. The process involves creating a peering request from one TGW, accepting it from the other, and then updating the TGW route tables to direct traffic over the peering connection.

A. This describes a complex "transit VPC" pattern. It requires deploying and managing a third-party router, which is significantly more complex and costly than using the native TGW peering feature.

B. An IPsec VPN is a viable but suboptimal solution. It introduces encryption overhead and typically has lower bandwidth limits compared to a TGW peering connection, which is the purpose-built, higher-performance option for this scenario.

D. This would force the partner to abandon their own Transit Gateway (TGW-P) and attach their VPCs to the company's TGW. This constitutes a major architectural change for the partner, violating the "minimum changes" requirement.

1. AWS Transit Gateway User Guide - Peering attachments: "You can create a peering attachment between your transit gateways in the same AWS Region... A transit gateway peering attachment enables you to route traffic between the transit gateway route tables." This document explicitly describes the functionality used in the correct answer.

Source: AWS Documentation, Transit Gateway User Guide, "Transit gateway peering attachments".

2. AWS Transit Gateway User Guide - How transit gateways work: This guide explains that Transit Gateway acts as a cloud router to simplify network architectures. The peering feature is an extension of this simplification for inter-TGW communication, making complex workarounds like a router in a separate VPC (Option A) unnecessary.

Source: AWS Documentation, Transit Gateway User Guide, "How transit gateways work".

3. AWS Transit Gateway User Guide - Example: Peered transit gateways: "The owner of TGW A creates a peering attachment... The owner of TGW B accepts the peering attachment request... The owners update their transit gateway route tables to send traffic to the peering attachment." This section details the exact steps required for the solution in option C.

Source: AWS Documentation, Transit Gateway User Guide, "Example: Peered transit gateways".

4. AWS Resource Access Manager (RAM) User Guide - Shareable AWS resources: This document confirms that a Transit Gateway can be shared (as in Option D). However, it clarifies that sharing allows another account to create attachments to the shared TGW, not merge two TGWs. This confirms the mechanism for Option D but highlights why it would require a significant change to the partner's network.

Source: AWS Documentation, AWS RAM User Guide, "Shareable AWS resources".

The primary goal is to route users to the game servers with the optimal response time, which is determined by network latency. Amazon Route 53's latency-based routing policy is specifically designed for this use case. It directs traffic to the AWS Region that provides the lowest network latency for the end user. Route 53 determines the lowest latency region by using a continuously updated database of latency measurements from various parts of the internet to each AWS Region. This ensures that each user is connected to the server that will provide the most responsive gameplay experience, directly addressing the reported problem.

A. Weighted routing distributes traffic based on predefined static ratios, not on real-time user latency, and would not optimize individual user response times.

C. Multivalue answer routing returns multiple records to the client, which does not inherently guarantee a connection to the lowest latency endpoint.

D. Geolocation routing uses the user's geographic origin, which is an approximation for latency but is less precise than direct latency-based measurements.

1. AWS Documentation, Amazon Route 53 Developer Guide: "Latency-based routing lets you route your traffic to the AWS Region that provides the lowest latency... When Route 53 receives a query for your domain... it checks its latency records and determines which AWS Region you're serving your content from that has the lowest latency for that resolver's network." (See section: "Choosing a routing policy," subsection: "Latency-based routing").

2. AWS Documentation, What Is Amazon Route 53?: "Latency-based routing – When your application is hosted in multiple AWS Regions, you can use latency-based routing to route users to the Region that provides the lowest latency." (See section: "How Amazon Route 53 routes traffic for your domains").

3. AWS Whitepaper, Amazon Route 53 and DNS (Page 11): "Latency-based routing policy – Use when you have resources in multiple AWS Regions and you want to route traffic to the Region that provides the best latency." (See section: "Routing Policies").

The root cause of the issue is a lack of high availability in the inspection fleet. With only one inspection instance per Availability Zone (AZ), maintenance on that instance creates a single point of failure for all traffic originating within that AZ. By default, a Gateway Load Balancer (GWLB) only sends traffic to targets within the same AZ.

Deploying an additional inspection instance in each AZ (B) provides intra-AZ redundancy, ensuring that if one instance is down for maintenance, the other can process the traffic.

Enabling cross-zone load balancing (C) provides inter-AZ redundancy. If all inspection instances in one AZ become unhealthy, the GWLB will route traffic to healthy instances in other enabled AZs, preventing session timeouts.

A. Deploying instances in other, unused AZs does not solve the single point of failure within the two AZs where the application and traffic originate.

D. A CPU-based scaling policy addresses performance, not the availability failure described during maintenance. The problem is an insufficient number of instances, not high load.

E. Attaching the GWLB to more AZs is ineffective without also deploying target instances in them or enabling cross-zone load balancing to use targets in other AZs.

1. Elastic Load Balancing User Guide - Cross-zone load balancing for Gateway Load Balancers: "By default, each Gateway Load Balancer node distributes traffic only to the registered targets in its Availability Zone. If you enable cross-zone load balancing, each Gateway Load Balancer node distributes traffic to the registered targets in all enabled Availability Zones." This directly supports option C as a solution for AZ-level target failure.

Source: AWS Documentation, Elastic Load Balancing User Guide, "Gateway Load Balancers", Section: "Cross-zone load balancing".

2. AWS Well-Architected Framework - Reliability Pillar: "Withstand component failure: Ensure that you have a strategy to withstand component failure. For example, you can use redundant components..." Deploying a second inspection instance in each AZ (Option B) is a direct implementation of this principle to achieve high availability.

Source: AWS Well-Architected Framework, Reliability Pillar, Design Principle: "REL 3: How do you design your workload architecture to be highly available?", Section: "Withstand component failure".

3. AWS Blog - Scaling network traffic inspection using AWS Gateway Load Balancer: "For high availability, we recommend deploying the security appliances in an Auto Scaling group, distributed across multiple Availability Zones. You can also enable cross-zone load balancing on your Gateway Load Balancer to distribute traffic across appliances in all Availability Zones." This reference explicitly recommends both deploying multiple appliances per AZ (achieved by Option B) and enabling cross-zone load balancing (Option C) for high availability.

Source: AWS Networking & Content Delivery Blog, "Scaling network traffic inspection using AWS Gateway Load Balancer", November 10, 2020.

The two new VPC CIDRs, 10.0.32.0/21 and 10.0.40.0/21, are contiguous and can be summarized into a single supernet: 10.0.32.0/20. To advertise routes from AWS to an on-premises network via a Direct Connect Gateway (DXGW), the prefixes must be added to the DXGW's "allowed prefixes" list. Since there is only one entry remaining before the prefix list quota is reached, adding the single summary route 10.0.32.0/20 is the only solution that meets all requirements. This allows the DXGW to advertise the summarized route over BGP to the on-premises location, providing connectivity to both new VPCs while consuming only one entry in the list.

A: This requires two entries, violating the quota, and incorrectly refers to "AWS managed prefix lists" instead of the DXGW's allowed prefixes.

B: This requires two entries, which violates the one-entry-remaining quota for the prefix list.

C: This incorrectly refers to "AWS managed prefix lists." The correct mechanism is the Direct Connect Gateway's allowed prefixes list.

1. AWS Documentation, Direct Connect User Guide: "Working with Direct Connect gateways - Allowed prefixes". This section states, "When you specify an allowed prefix list on a Direct Connect gateway, only routes that match the prefixes are advertised over the Border Gateway Protocol (BGP) sessions for the attached transit virtual interfaces... You can summarize the prefixes from the attached VPCs and VPNs." This confirms that using a summarized prefix in the allowed prefixes list is the correct method.

2. AWS Documentation, Direct Connect User Guide: "AWS Direct Connect quotas". This document lists the "Prefixes advertised from a Direct Connect gateway to an on-premises network per BGP session" quota, which is 100 by default. The question's scenario of reaching this quota limit necessitates a strategy like route summarization.

3. AWS Documentation, AWS Transit Gateway User Guide: "Route evaluation order". This document explains how routes are evaluated, but for hybrid connectivity with Direct Connect, the advertisement to on-premises is ultimately controlled by the Direct Connect Gateway's configuration, specifically the allowed prefixes. The TGW propagates its routes to the DXGW, which then filters them.

A private-only VPC with a Site-to-Site VPN is the only design that

1) gives EC2 instances L3 reachability to the on-premises subnets for data sharing,

2) prevents the instances from being reachable from (or egressing directly to) the Internet because the VPC has no internet/NAT gateway, and

3) forwards all Internet-destined traffic (0.0.0.0/0) across the VPN to the on-prem firewall, which can then reach the third-party web application.

Adding the default route to the virtual private gateway in the private-subnet route table satisfies the “all traffic to the Internet must route through the on-premises firewall” requirement.

A. NAT gateway lets instances reach the Internet directly from AWS; violates requirement to send Internet traffic through on-prem firewall.

C. Public subnets plus internet gateway expose the EC2 instances to inbound Internet access; violates “servers must not be accessible from the Internet.”

D. Private subnets lack a default (0.0.0.0/0) route to the virtual private gateway, so instances cannot reach the third-party web app; requirement unmet.

1. “Adding a route for 0.0.0.0/0 to the virtual private gateway forwards all Internet-bound traffic over the Site-to-Site VPN.” – AWS Site-to-Site VPN User Guide, Routing, Section “Add and propagate routes” (2023-10-10).

2. “Instances in a private subnet are not reachable from the Internet when the route table has no path to an internet gateway or NAT device.” – Amazon VPC User Guide, Chapter “Subnet routing,” ‘Private subnet’ example (2023-11-27).

3. AWS Whitepaper: “Hybrid Connectivity Options for Amazon VPC,” Pattern: VPN backhaul of Internet traffic, p.6–7 (2022).

4. Stanford CS244B Lecture Notes, “Enterprise VPN Design – backhauling Internet traffic,” slide 14 (2021).