How to Cost-Effectively Monitor School Site-to-Site VPN Connectivity Loss?
An education agency is preparing for its annual competition between schools. In the competition, students at schools from around the country solve math problems, complete puzzles, and write essays. The IP addressing plan of all the schools is well-known and is administered centrally. The competition is hosted in the AWS Cloud and is not publicly available. All competition traffic must be encrypted in transit. Only authorized endpoints can access the competition. All the schools have firewall policies that block ICMP traffic. A network engineer builds a solution in which all the schools access the competition through AWS Site-to-Site VPN connections. The network engineer uses BGP as the routing protocol. The network engineer must implement a solution that notifies schools when they lose connectivity and need to take action on their premises to address the issue. Which combination of steps will meet these requirements MOST cost-effectively? (Choose two.)
Community Votes
78% of anonymous learners picked answer AE. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
This question tests your understanding of how AWS Site-to-Site VPN tunnel metrics and BGP route propagation can be used together as low-cost connectivity signals. The common trap is picking a generic reachability or ping solution without considering ICMP blocks and the per-invocation cost of advanced diagnostics.
The most cost-effective approach to notify schools when Site-to-Site VPN connectivity drops is to combine CloudWatch alarms on VPN tunnel state with a scheduled Lambda function that checks for the removal of BGP-propagated routes. Community consensus strongly favors AE because it relies on native monitoring and avoids expensive per-invocation tools or ICMP-based checks.
Many candidates select Option C because VPC Reachability Analyzer sounds like a precise way to verify connectivity, but it is not cost-effective for continuous monitoring and cannot detect failures entirely on the customer-premises side. Option B is another popular wrong choice because it relies on ICMP ping, which the schools' firewalls explicitly block.
Community Discussion (6 comments)
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Expert Analysis
Overview
When designing connectivity monitoring for AWS Site-to-Site VPN connections, you need a solution that detects loss of connectivity from both the AWS side and the school's on-premises side, while keeping costs low. The scenario already uses BGP as the routing protocol, so route propagation provides a built-in signal of a healthy BGP session.
Why Option A Is Correct
Option A uses Amazon CloudWatch to monitor the state of the VPN tunnels. AWS Site-to-Site VPN publishes a TunnelState CloudWatch metric for each VPN tunnel. A CloudWatch alarm can be set to trigger when this metric equals 0 (down). The alarm then publishes to an Amazon SNS topic, which can send email or other notifications to people at the affected school.
This approach is natively integrated, requires no additional compute, and is very cost-effective. CloudWatch alarms and SNS notifications have a predictable low pricing model, making them the first choice for tunnel health monitoring.
Why Option E Is Correct
Option E addresses the on-premises side of the connectivity. With a BGP-enabled Site-to-Site VPN, the school's on-premises routes are propagated to the VPC route table when the BGP session is established. If the BGP session fails, or the school loses connectivity, AWS removes those propagated routes from the VPC route table.
A scheduled AWS Lambda function can check the VPC route table for the presence of each school's known routes. If a route disappears, the Lambda function can publish an SNS notification to that school. This is a lightweight, cost-effective monitoring method because it simply reads route table entries on a schedule and does not generate per-analysis charges or depend on ICMP.
Together, Options A and E monitor both the AWS-side tunnel state and the on-premises BGP route announcement, giving schools clear notification when they need to investigate their own equipment.
Why Option B Is Wrong
Option B proposes a scheduled Lambda function that pings each school's customer gateway device. However, the school firewall policies explicitly block ICMP traffic, so the ping will always fail. Even if ICMP were allowed, relying on ping is not a complete measure of VPN or BGP health. This option is therefore invalid in this scenario.
Why Option C Is Wrong
Option C suggests using the VPC Reachability Analyzer API on a schedule. While Reachability Analyzer can help debug network paths, it has per-invocation costs and is not designed as a continuous monitoring service. It also cannot look beyond AWS boundaries into the school's on-premises network. If the school's customer gateway or internet connection fails, Reachability Analyzer may still report that the AWS-side path is valid, or it may fail to verify end-to-end connectivity. Community comments highlight that it is not cost-effective and cannot detect issues that originate entirely at the school.
Why Option D Is Wrong
Option D creates CloudWatch dashboards for each school. Dashboards are passive views and do not proactively notify anyone when connectivity drops. They do not satisfy the requirement to notify schools when they lose connectivity and need to take action. Dashboards also add cost and management overhead without providing the necessary alerting capability.
Community Consensus
The community vote distribution is overwhelmingly in favor of AE (78 votes versus 22 for AC). Commenters correctly point out that Option B fails due to ICMP blocking, Option C is too expensive for continuous checks, and Option D is not a notification mechanism. Route table monitoring in Option E is a clever way to detect when BGP routes vanish, which is a strong indicator that the school's VPN connection is down and may need on-premises action.
Conclusion
The correct combination is Option A + Option E. It uses CloudWatch for tunnel-level monitoring and Lambda for BGP route presence monitoring, both connected to SNS for notifications. This gives a cost-effective, scalable, and accurate way to alert schools when they lose connectivity and need to act on their premises.
Official Reference
Exam Strategy
When a question asks for the most cost-effective solution, prefer options that use built-in AWS monitoring and event-driven notifications over scheduled, per-invocation diagnostics. Also, if ICMP is blocked, immediately eliminate ping-based options and look for solutions based on CloudWatch metrics or BGP route table state.
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