- A
Use Amazon ElastiCache to store the mapping in memory.
Why wrong: ElastiCache is in-memory but not persistent; data is lost on failure.
- B
Use Amazon DynamoDB to store the mapping, with user identity as the partition key and connectionId as an attribute.
DynamoDB is ideal for this use case due to its low latency and scalability.
- C
Use Amazon RDS to store the mapping in a relational database.
Why wrong: RDS is overkill and adds latency compared to DynamoDB.
- D
Use Amazon S3 to store the mapping as a JSON file.
Why wrong: S3 is not designed for frequent low-latency updates.
Question 621 of 1,616
Store WebSocket ConnectionId Mapping in DynamoDB
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 Amazon API Gateway WebSocket APIs and AWS Lambda. The application needs to send messages to connected clients. The developer notices that the 'connectionId' changes every time a client reconnects. How should the developer store the mapping between user identity and connectionId?
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
✓
Use Amazon DynamoDB to store the mapping, with user identity as the partition key and connectionId as an attribute.
Option B is correct because DynamoDB provides a fully managed, serverless key-value store that can persist the mapping between user identity and connectionId with low latency. Since connectionId changes on each reconnect, a durable database like DynamoDB ensures the mapping survives Lambda cold starts and scales automatically with the number of connected users, which is essential for a real-time chat application.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 Amazon ElastiCache to store the mapping in memory.
Why it's wrong here
ElastiCache is in-memory but not persistent; data is lost on failure.
- ✓
Use Amazon DynamoDB to store the mapping, with user identity as the partition key and connectionId as an attribute.
Why this is correct
DynamoDB is ideal for this use case due to its low latency and scalability.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use Amazon RDS to store the mapping in a relational database.
Why it's wrong here
RDS is overkill and adds latency compared to DynamoDB.
- ✗
Use Amazon S3 to store the mapping as a JSON file.
Why it's wrong here
S3 is not designed for frequent low-latency updates.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume an in-memory cache like ElastiCache is sufficient for state persistence, but they overlook that Lambda functions are stateless and the mapping must survive across invocations and cold starts, making a durable database like DynamoDB the correct choice.
Detailed technical explanation
How to think about this question
Under the hood, API Gateway WebSocket APIs generate a unique connectionId per connection, which is passed to the Lambda function via the $connect route. DynamoDB’s partition key on user identity allows O(1) lookups to retrieve the current connectionId, and the Lambda function can use the ApiGatewayManagementApi.postToConnection endpoint to send messages directly to that connection. In a real-world scenario, you would also store a timestamp attribute to implement idle connection cleanup, ensuring stale entries are removed when clients disconnect.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
What to study next
Got this wrong? Here's your next step.
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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 — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use Amazon DynamoDB to store the mapping, with user identity as the partition key and connectionId as an attribute. — Option B is correct because DynamoDB provides a fully managed, serverless key-value store that can persist the mapping between user identity and connectionId with low latency. Since connectionId changes on each reconnect, a durable database like DynamoDB ensures the mapping survives Lambda cold starts and scales automatically with the number of connected users, which is essential for a real-time chat application.
What should I do if I get this DVA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 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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