How Do You Add Failover to a Single-AZ RDS for MySQL Instance?
A company has an application that runs on Amazon EC2 instances. The application stores data on an Amazon RDS for MySQL Single-AZ DB instance. Requests to the DB instance from the application include reads and writes. A CloudOps engineer must implement a solution that provides failover for the DB instance. The solution must minimize application downtime. Which solution will meet these requirements?
Community Insight
The exam tests whether you know which RDS feature provides automatic failover versus which features merely improve availability or connection handling; the trap is picking RDS Proxy or a read replica because they sound like resilience tools.
Converting an RDS for MySQL Single-AZ DB instance to a Multi-AZ DB instance deployment gives the application automatic failover to a synchronous standby in another Availability Zone with minimal downtime. This page confirms that option A is the only choice that actually delivers failover for both reads and writes at the existing endpoint.
Choosing RDS Proxy (D) because it is described as improving availability during failover — RDS Proxy manages connections and can shorten failover impact, but it does not itself create or provide the failover mechanism.
Community Discussion (1 comments)
Comments & Corrections
No comments yet — spotted an error or have a note? Share it below.
Expert Analysis
Why the Answer Is Correct
A Multi-AZ DB instance deployment maintains a synchronously replicated standby in a different Availability Zone, and Amazon RDS automatically fails over to that standby if the primary fails, with the DNS endpoint following the new primary. Because replication is synchronous and the same endpoint is reused, the application keeps performing both reads and writes after a short failover interval, which directly satisfies "provide failover" and "minimize application downtime." No application connection string changes are required, so this is the lowest-effort, lowest-downtime option for a Single-AZ MySQL instance holding mixed read/write traffic. That is why option A is the only solution that both provides failover and keeps writes flowing. The community also converged on this point, as Bad_Mat's vote for option A reflects the standard RDS failover doctrine.Why the Other Options Are Wrong
A read replica (B) is asynchronous, is read-only, and must be promoted manually; placing it in the same Availability Zone as the primary also means a zonal failure takes both down, so it provides neither automatic failover nor downtime reduction for writes. An Auto Scaling group (C) is an EC2 construct and cannot contain an RDS DB instance at all, so it does nothing for database failover. RDS Proxy (D) pools and multiplexes application connections and can make failover gentler by holding connections open, but it does not itself create a standby or trigger failover — it is a complement to Multi-AZ, not a replacement, and on its own leaves a Single-AZ instance as a single point of failure.Community Comment Notes
Engagement on this item is light, with Bad_Mat casting the only recorded vote for option A, matching the Multi-AZ DB instance answer. The lack of dissent is typical for this scenario, because the distractors are easy to dismiss once you recall that read replicas and RDS Proxy do not perform failover. Treat the agreement as a sanity check rather than proof, and anchor your reasoning in the synchronous standby behavior of Multi-AZ.Official Reference
Exam Strategy
When a question asks for "failover" with "minimal downtime" on an RDS instance, immediately look for Multi-AZ (DB instance or DB cluster) and eliminate anything that is read-only, connection-pooling, or an EC2 scaling construct. RDS Proxy frequently appears as a decoy — remember it reduces failover impact but is never the failover mechanism itself.
Frequently Asked Questions
Why doesn't RDS Proxy provide the required failover for this DB instance?
RDS Proxy only pools and manages connections; it needs an already highly available database behind it. Without Multi-AZ, the Single-AZ instance remains a single point of failure.
Can an Auto Scaling group make the RDS DB instance highly available?
No. Auto Scaling groups scale EC2 instances, not RDS databases. Failover for RDS comes from Multi-AZ deployments, not scaling groups.
Related Analysis
Practice All SOA-C03 Questions
Access 100 questions with complete answers and detailed explanations.
View Full SOA-C03 Practice Test →