The original question was about handling a situation where the database is unavailable due to an upgrade, not a failover situation. During a database upgrade, the database instance is not available, and RDS Proxy would not be able to connect to a new database instance because there isn’t one. In this specific scenario, using Amazon SQS as described in option D provides a buffer for the incoming data during the period when the database is unavailable. This ensures that no data is lost, and it can be written to the database once the upgrade is complete.

This is MySQL Database. RDS proxy = no no

Aurora supports RDS proxy! https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/rds-proxy.html

This is incorrect as nowhere in the question is mentioned the RDS have more than 1 instance. So... when the instance is down for maintenance there is no second instance to which RDS Proxy can redirect the requests. The correct answer is D.

It does, according to that link

You can use RDS Proxy with Aurora Serverless v2 clusters but not with Aurora Serverless v1 clusters. https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/rds-proxy.html

This not RDS supports Aurora mysl database. All the limitations listed in the link you posted above are not related to the question, hence the answer is B

Actually RDS Proxy supports Aurora DBs running on PostgreSQL and MySQL. https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/Concepts.Aurora_Fea_Regions_DB-eng.Feature.RDS_Proxy.html With RDS proxy, you only expose a single endpoint for request to hit and any failure of the primary DB in a Multi-AZ configuration is will be managed automatically by RDS Proxy to point to the new primary DB. Hence RDS proxy is the most efficient way of solving the issue as additional code change is required. https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/rds-proxy.howitworks.html

From Amazon Q: RDS Proxy can be used with Amazon Aurora. Here are some key points about using RDS Proxy with Aurora: RDS Proxy supports connecting to Aurora MySQL and Aurora PostgreSQL databases. This allows applications to connect to Aurora clusters via the proxy. Using a proxy provides better scalability by allowing connections to be distributed among Aurora replica instances. It also improves availability since the proxy can direct connections to other Aurora replicas if the primary becomes unavailable. The Aurora database and RDS Proxy must be in the same VPC to allow connections. Your applications can be deployed in the same VPC or a different one, as long as they have network access to the proxy. Certain regions and Aurora engine versions support RDS Proxy based on the database engine. You can check the AWS documentation for the latest supported versions in each region.

Ignore my answer, it has to be D.

Given the requirement to ensure customer data is not lost during database upgrades when Lambda functions fail to establish connections, the most appropriate solution is to decouple the Lambda functions from the database using a queueing mechanism. This way, the customer data can be temporarily stored and processed independently of the database availability. Option D, which suggests storing customer data in an Amazon SQS FIFO queue and creating a new Lambda function to poll the queue and store the data in the database, aligns with this requirement and is the recommended solution.

D is correct. If the Lambda function fails, it does not remove the message from the queue, thus it will be picked up again. A is nonsense because during database upgrades, there is no available database. RDS proxy helps to fail over, but there is nothing that you could fail over to.

But only if there is a second instance that you can fail over to.