Jeff’s Note #
Unlike generic exam dumps, ADH analyzes this scenario through the lens of a Real-World Lead Developer.
For AWS DVA-C02 candidates, the confusion often lies in properly managing how your application handles DNS resolution for database endpoints. In production, this is about knowing exactly how DNS caching at the application level can impact load distribution across database read replicas. Let’s drill down.
The Certification Drill (Simulated Question) #
Scenario #
ShopWave is a fast-growing e-commerce platform with a backend powered by Amazon Aurora MySQL. To enhance read query performance, ShopWave’s database team configured multiple read replicas alongside the primary Aurora cluster. However, the engineering team notices that nearly all read traffic is directed to just one of the Aurora read replicas, while the others remain underutilized and idle.
The Requirement: #
Ensure a more even distribution of read traffic across all Aurora read replicas to fully leverage the database scaling capabilities.
The Options #
- A) Disable application-level DNS caching.
- B) Enable application-level DNS caching.
- C) Enable application connection pooling.
- D) Disable application connection pooling.
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leave a comment:
Correct Answer #
A) Disable application-level DNS caching.
Quick Insight: The Developer Imperative #
Application-level DNS caching causes the client to repeatedly use a single IP address for the Aurora cluster’s reader endpoint. Disabling DNS caching forces the application to resolve DNS more frequently, allowing AWS’s cluster endpoint to return the IP of varying read replicas, thus distributing traffic effectively.
Content Locked: The Expert Analysis #
You’ve identified the answer. But do you know the implementation details that separate a Junior from a Senior?
The Expert’s Analysis #
Correct Answer #
Option A) Disable application-level DNS caching.
The Winning Logic #
Amazon Aurora’s reader endpoint uses DNS round-robin to distribute connections among its replicas. The underlying mechanism depends on frequent DNS lookups to return different IP addresses — each corresponding to a distinct read replica. When an application caches DNS entries for too long, the same IP address—and thus the same replica—is always reused, causing uneven load distribution.
Disabling application-level DNS caching forces the app to resolve the reader endpoint DNS name more often, allowing the client to receive updated IPs pointing to different read replicas. This balances traffic and improves scalability without changing database or AWS configurations.
The Trap (Distractor Analysis): #
-
Why not B) Enable application-level DNS caching?
This would worsen the issue by increasing the chance that the client sticks with one cached IP address, bottlenecking reads to a single replica. -
Why not C) Enable application connection pooling?
Connection pooling helps with resource reuse but does not affect DNS resolution or the IP addresses used. Pooling connections to a single cached IP won’t distribute load across replicas. -
Why not D) Disable application connection pooling?
Disabling pooling reduces connection reuse efficiency, leading to overheads without addressing the core load distribution problem.
The Technical Blueprint #
B) For Developer / SysOps (Code/CLI Snippet):
Here’s an example snippet for a Java-based application using the HikariCP connection pool that disables DNS caching by configuring the JVM:
# Disable DNS caching by setting Java security property to 0 seconds TTL
java -Dsun.net.inetaddr.ttl=0 -jar your-app.jar
Or programmatically inside the application before creating connections:
java.security.Security.setProperty("networkaddress.cache.ttl", "0");
This forces Java’s internal DNS resolver to perform fresh DNS lookups for each connection, balancing Aurora read replica usage properly.
The Comparative Analysis #
| Option | API/Config Area | Performance Impact | Use Case / Outcome |
|---|---|---|---|
| A | DNS caching (runtime) | Distributes read traffic evenly | Correct approach for Aurora replicas |
| B | DNS caching (runtime) | Pinpoints to one replica | Increases hotspot risk, NOT recommended |
| C | Connection Pooling | Efficient connection reuse | Helps performance but does NOT balance replicas |
| D | Connection Pooling | Adds overhead (no reuse) | Worsens performance, no effect on replica choice |
Real-World Application (Practitioner Insight) #
Exam Rule #
“For the exam, always pick disabling application-level DNS caching when you see uneven traffic to Aurora read replicas.”
Real World #
“In production, DNS caching is often enabled by default at the OS or application runtime level to improve latency. But for Aurora reader endpoints, turning it off or reducing TTL is critical to avoid throttling one replica while others idle.”
(CTA) Stop Guessing, Start Mastering #
Disclaimer
This is a study note based on simulated scenarios for the AWS DVA-C02 exam.