- A
Use an SQS FIFO queue to store connection IDs and have a Lambda function poll the queue to broadcast.
Why wrong: SQS is not designed for real-time broadcasting and adds latency.
- B
Store connection IDs in a DynamoDB table. Use a Lambda function to query all connection IDs and send messages using the API Gateway Management API.
DynamoDB is fully managed, scalable, and cost-effective for storing and retrieving connection IDs.
- C
Maintain an in-memory list of connection IDs in a global variable of a single Lambda function.
Why wrong: Lambda functions are stateless and can have multiple concurrent instances; in-memory lists are not shared.
- D
Use Amazon ElastiCache Redis to store connection IDs and use Redis Pub/Sub for broadcasting.
Why wrong: This works but is more complex and expensive than DynamoDB for this purpose.
DVA-C02 Development with AWS Services Practice Question
This DVA-C02 practice question tests your understanding of development with aws services. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A developer is building a real-time chat application using WebSockets via API Gateway. The backend uses AWS Lambda functions to handle connect, disconnect, and message events. The application needs to broadcast messages to all connected clients. What is the most scalable and cost-effective way to maintain the list of connection IDs and broadcast messages?
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
Store connection IDs in a DynamoDB table. Use a Lambda function to query all connection IDs and send messages using the API Gateway Management API.
Option A is correct. DynamoDB is a scalable, low-latency database that can store connection IDs and allow Lambda to query all connections for broadcasting. Option B is wrong because an in-memory list in a single Lambda instance does not scale across multiple instances. Option C is wrong because ElastiCache is more expensive and complex than DynamoDB for this use case. Option D is wrong because SQS is not designed for real-time broadcasting and would require polling.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use an SQS FIFO queue to store connection IDs and have a Lambda function poll the queue to broadcast.
Why it's wrong here
SQS is not designed for real-time broadcasting and adds latency.
- ✓
Store connection IDs in a DynamoDB table. Use a Lambda function to query all connection IDs and send messages using the API Gateway Management API.
- ✗
Maintain an in-memory list of connection IDs in a global variable of a single Lambda function.
Why it's wrong here
Lambda functions are stateless and can have multiple concurrent instances; in-memory lists are not shared.
- ✗
Use Amazon ElastiCache Redis to store connection IDs and use Redis Pub/Sub for broadcasting.
Why it's wrong here
This works but is more complex and expensive than DynamoDB for this purpose.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DVA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this DVA-C02 question test?
Development with AWS Services — This question tests Development with AWS Services — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Store connection IDs in a DynamoDB table. Use a Lambda function to query all connection IDs and send messages using the API Gateway Management API. — Option A is correct. DynamoDB is a scalable, low-latency database that can store connection IDs and allow Lambda to query all connections for broadcasting. Option B is wrong because an in-memory list in a single Lambda instance does not scale across multiple instances. Option C is wrong because ElastiCache is more expensive and complex than DynamoDB for this use case. Option D is wrong because SQS is not designed for real-time broadcasting and would require polling.
What should I do if I get this DVA-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DVA-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
This DVA-C02 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 DVA-C02 exam.
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