ANS-C01 Network Design Practice Question
A company is designing a network for a critical application that requires high availability across two AWS Regions (us-east-1 and us-west-2). The application uses an Application Load Balancer (ALB) in each region, with Auto Scaling groups behind them. The database is an Amazon Aurora Global Database with a primary cluster in us-east-1 and a secondary cluster in us-west-2. The company wants to use Amazon Route 53 to route traffic to the closest healthy ALB. They also need to ensure that if the primary database fails over to the secondary region, the application can still write to the database with minimal latency. Additionally, the application must be able to read from the local database in each region for read-intensive workloads. The network team has designed the following: Route 53 with latency-based routing and health checks for the ALBs. The application instances in each region are configured to connect to the local Aurora cluster endpoint. For writes, they use the global writer endpoint. What is the MOST significant design flaw?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Route 53 health checks only monitor the ALB endpoint, not the overall application health including database connectivity
The design flaw is that Route 53 health checks only monitor the ALB endpoint, not the overall application health including database connectivity. If the database in a region fails (e.g., due to a failure in the primary or secondary cluster), the ALB might still be healthy, and Route 53 would continue to route traffic to that region. However, the application instances would not be able to serve requests properly because they rely on the local database. A robust health check should include checking the application's ability to connect to the database and perform basic operations. This ensures that traffic is only routed to regions where the full application stack is healthy. Other options are less significant: A (lifecycle hooks) is a minor optimization, C (write latency) is inherent to the architecture and might be acceptable for critical writes, and D is false because Aurora Global Database does support cross-region replication.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The Auto Scaling groups are not configured with lifecycle hooks to drain connections during scale-in
Why it's wrong here
This is important but not the most significant for high availability across regions.
- ✓
The Route 53 health checks only monitor the ALB endpoint, not the overall application health including database connectivity
Why this is correct
If the database fails in a region, the ALB might still be healthy, causing traffic to be sent to a region that cannot serve requests.
- ✗
The application instances in us-west-2 experience high latency for write operations due to cross-region traffic to the primary database
Why it's wrong here
This is a known trade-off, but not necessarily a design flaw as global database is designed for disaster recovery, not active-active writes.
- ✗
The Aurora Global Database does not support cross-region replication for read replicas
Why it's wrong here
Aurora Global Database supports cross-region replication for reads.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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