SAP-C02 Continuous Improvement for Existing Solutions Practice Question
A company uses Amazon RDS for MySQL with Multi-AZ deployment. During a recent failover, the application experienced a 5-minute downtime. The application uses a connection pool with a 30-second connection timeout. The RDS DNS name is used as the endpoint. What is the MOST likely cause of the downtime?
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 DNS TTL for the RDS endpoint is set too high
During an RDS Multi-AZ failover, the DNS name remains the same but the underlying IP address changes. If the DNS TTL is set too high (default is 60 seconds but can be configured higher), clients may continue to use the old cached IP address for the duration of the TTL, leading to connection failures until the cache expires. This explains the 5-minute downtime, as the application's connection pool with a 30-second timeout cannot recover until the DNS record is refreshed. Option B is incorrect because the 30-second timeout is sufficient to wait for failover, but the issue is DNS propagation, not timeout duration. Option C is incorrect because Multi-AZ failover typically completes within 1-2 minutes, not 5 minutes. Option D is incorrect because the endpoint (DNS name) does not change after failover; only the IP 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 DNS TTL for the RDS endpoint is set too high
Why this is correct
High DNS TTL causes clients to cache the old IP, leading to connection failures until cache expires.
- ✗
The connection pool timeout is too short to allow failover
Why it's wrong here
30-second timeout is sufficient; the issue is longer due to DNS caching.
- ✗
The Multi-AZ failover took longer than expected
Why it's wrong here
RDS failover usually completes within 2 minutes.
- ✗
The application is using the wrong endpoint after failover
Why it's wrong here
The DNS name does not change after failover.
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