DBS-C01 Management and Operations Practice Question
A company is running an Amazon RDS for MySQL Multi-AZ DB instance. The primary instance in us-east-1a experiences an unexpected failure. After the automatic failover, the application team reports that write latency has increased significantly. The new primary instance is in us-east-1b. The DB instance class and storage configuration are identical. What is the MOST likely cause of the increased write latency?
⚠ Common exam trap
Watch out — candidates often assume Multi-AZ failover is transparent and does not affect performance, but cross-AZ network latency for writes can increase significantly if the application remains in the original AZ.
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 application is connecting to the DB instance in a different Availability Zone, increasing network latency.
After failover, the new primary DB instance resides in us-east-1b, while the application likely continues to connect to the original endpoint or is still running in us-east-1a. This cross-AZ network hop introduces additional latency for write operations, as the application must send data over the network between Availability Zones. The DB instance class and storage are identical, so performance differences are not due to hardware changes.
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 DB instance class in us-east-1b is a different size than the original.
Why it's wrong here
The instance class and storage are identical.
- ✓
The application is connecting to the DB instance in a different Availability Zone, increasing network latency.
Why this is correct
The new primary is in us-east-1b, and if the application is in us-east-1a, cross-AZ latency increases write latency.
- ✗
The Multi-AZ configuration uses asynchronous replication, causing higher latency.
Why it's wrong here
Multi-AZ uses synchronous replication.
- ✗
The new primary is in the same Availability Zone as the application, but the standby is in a different AZ, causing synchronous replication overhead.
Why it's wrong here
Multi-AZ synchronous replication only occurs between primary and standby, not between primary and application.
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