SAA-C03 Design Secure Architectures Practice Question
A mobile app reads the same product details many times per minute from Amazon DynamoDB. The table design is already correct, but repeated reads are still causing noticeable latency. Which service should the team add to improve read performance?
⚠ Common exam trap
Candidates often confuse DAX with ElastiCache (which is generic and not DynamoDB-native) or assume that Lambda or SNS can somehow accelerate reads, but DAX is the only service purpose-built for DynamoDB read acceleration.
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
✓
Amazon DAX
Amazon DAX (DynamoDB Accelerator) is an in-memory cache specifically designed for DynamoDB. It reduces read latency from single-digit milliseconds to microseconds by caching frequently accessed items, which directly addresses the repeated read pattern described in the question.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Amazon DAX
Why this is correct
Amazon DAX is a DynamoDB-compatible in-memory caching service that delivers up to 10x read performance improvement, reducing read latency from single-digit milliseconds to microseconds. It sits in front of your DynamoDB tables and transparently intercepts repeated read calls, serving them from the cache without additional application code. This makes DAX the correct choice for a mobile app that reads identical product details many times, as it directly targets the repeated-read bottleneck by bypassing the database's disk access and reducing the load on DynamoDB.
- ✗
Amazon EFS
Why it's wrong here
Amazon EFS is a scalable, elastic NFS file system designed for use with AWS compute services like EC2, not for caching database queries. It stores files as objects in a file system hierarchy, whereas DynamoDB items are key-value records accessed via a database API. Adding EFS to this architecture would require the mobile app or a backend service to read product details from DynamoDB, serialize them into files, and write them to EFS, then read those files on subsequent requests—introducing significant overhead and complexity without providing the fast, in-memory read acceleration that DAX offers.
When this WOULD be correct
A question where an application running on multiple EC2 instances needs a shared, scalable file system for storing and accessing common files (e.g., configuration files, logs, or media) across instances. EFS would be the correct choice for a shared NFS file system.
- ✗
AWS Lambda
Why it's wrong here
AWS Lambda is a serverless compute service that executes code in response to events, but it does not inherently cache data or accelerate DynamoDB read operations. While a Lambda function could be used as a middleware layer to fetch data from DynamoDB and store it in an external cache like DAX or ElastiCache, Lambda itself has no built-in caching mechanism. In this scenario, simply using Lambda without a dedicated caching service would add compute execution time and network round-trips between Lambda and DynamoDB, potentially increasing latency rather than reducing it for repeated reads.
When this WOULD be correct
A question where a DynamoDB stream triggers a function to transform or aggregate data before storing it elsewhere (e.g., update an Amazon ElastiCache cluster or write to Amazon S3) would make Lambda the correct answer. For example: 'A team needs to process item changes from a DynamoDB table and update a materialized view in near real time.'
- ✗
Amazon SNS
Why it's wrong here
Amazon SNS is a fully managed pub/sub messaging service used for decoupling components, sending notifications, and distributing events to a large number of subscribers. It is not designed to store or cache data, and it operates on a push-based model where messages are ephemeral and not persisted for repeated retrieval. Using SNS in the read path for product details would require the app to publish a request, subscribe to a response, and handle message delivery—adding network hops and asynchronous complexity that would increase latency and fail to address the need for low-latency repeated reads from DynamoDB.
When this WOULD be correct
A correct scenario: 'An application needs to send real-time alerts to multiple subscribers (e.g., email, SMS, Lambda) whenever a new item is inserted into a DynamoDB table.' In that case, Amazon SNS would be the right service to fan out notifications.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The SAA-C03 exam frequently reuses these exact scenarios with slightly different constraints.
✓Amazon DAXCorrect answer▾
Why this is correct
Amazon DAX is a DynamoDB-compatible in-memory caching service that delivers up to 10x read performance improvement, reducing read latency from single-digit milliseconds to microseconds. It sits in front of your DynamoDB tables and transparently intercepts repeated read calls, serving them from the cache without additional application code. This makes DAX the correct choice for a mobile app that reads identical product details many times, as it directly targets the repeated-read bottleneck by bypassing the database's disk access and reducing the load on DynamoDB.
✗Amazon EFSWrong answer — click to see why▾
Why this is wrong here
Amazon EFS is a file storage service for EC2 instances, not a caching layer for DynamoDB. It cannot reduce read latency for DynamoDB queries because it does not integrate with DynamoDB's API or provide in-memory acceleration.
★ When this WOULD be the correct answer
A question where an application running on multiple EC2 instances needs a shared, scalable file system for storing and accessing common files (e.g., configuration files, logs, or media) across instances. EFS would be the correct choice for a shared NFS file system.
Why candidates choose this
Candidates might confuse EFS as a general-purpose 'cache' because it offers low-latency file access, but they overlook that it is not designed for database query caching and cannot be used with DynamoDB directly.
✗AWS LambdaWrong answer — click to see why▾
Why this is wrong here
AWS Lambda is a compute service for running code in response to events, not a caching layer. It cannot reduce read latency for repeated DynamoDB reads because it does not cache data; adding Lambda would introduce additional invocation overhead, worsening latency.
★ When this WOULD be the correct answer
A question where a DynamoDB stream triggers a function to transform or aggregate data before storing it elsewhere (e.g., update an Amazon ElastiCache cluster or write to Amazon S3) would make Lambda the correct answer. For example: 'A team needs to process item changes from a DynamoDB table and update a materialized view in near real time.'
Why candidates choose this
Candidates may think Lambda can 'speed up' reads by preprocessing or caching data, but Lambda is stateless and not designed for low-latency data retrieval. The temptation comes from overgeneralizing Lambda's role in optimizing data pipelines.
✗Amazon SNSWrong answer — click to see why▾
Why this is wrong here
Amazon SNS is a pub/sub messaging service for notifications and event-driven workflows, not a caching layer. It cannot reduce read latency for repeated DynamoDB reads because it does not store or serve data from a cache.
★ When this WOULD be the correct answer
A correct scenario: 'An application needs to send real-time alerts to multiple subscribers (e.g., email, SMS, Lambda) whenever a new item is inserted into a DynamoDB table.' In that case, Amazon SNS would be the right service to fan out notifications.
Why candidates choose this
Candidates might think SNS can cache or buffer repeated reads because it's a managed service that can decouple components, but they confuse its notification role with caching or data serving capabilities.
Analysis generated from the official SAA-C03blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.