- A
Increase the Lambda function's memory allocation
Why wrong: Memory does not affect ordering.
- B
Use API Gateway's built-in message ordering feature
Why wrong: API Gateway does not provide ordering.
- C
Set the 'sequenceNumber' property in the WebSocket message
Why wrong: Clients must reorder; not a server-side solution.
- D
Use an Amazon SQS FIFO queue to buffer messages before processing
FIFO queues preserve order.
Question 280 of 1,616
Ensure Ordered Message Delivery in WebSocket API
This DVA-C02 practice question tests your understanding of development with aws services. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 WebSockets and AWS Lambda. The developer notices that messages are sometimes delivered out of order. What should the developer do to ensure ordered message delivery?
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 an Amazon SQS FIFO queue to buffer messages before processing
Amazon API Gateway WebSockets does not guarantee ordered delivery of messages because WebSocket frames can arrive out of order over the network. Using an Amazon SQS FIFO queue as a buffer ensures that messages are processed in the exact order they are sent, preserving the sequence required for a real-time chat application. The FIFO queue provides first-in-first-out delivery and exactly-once processing, which solves the out-of-order issue without requiring custom sequencing logic.
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.
- ✗
Increase the Lambda function's memory allocation
Why it's wrong here
Memory does not affect ordering.
- ✗
Use API Gateway's built-in message ordering feature
Why it's wrong here
API Gateway does not provide ordering.
- ✗
Set the 'sequenceNumber' property in the WebSocket message
Why it's wrong here
Clients must reorder; not a server-side solution.
- ✓
Use an Amazon SQS FIFO queue to buffer messages before processing
Why this is correct
FIFO queues preserve order.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume API Gateway WebSockets inherently preserves message order because it is a managed service, but the WebSocket protocol itself does not guarantee ordering, and AWS does not add that guarantee at the API Gateway layer.
Detailed technical explanation
How to think about this question
Amazon SQS FIFO queues use a deduplication ID and message group ID to ensure strict ordering within a group; for a chat application, each chat session or user pair can be assigned a unique message group ID to maintain per-conversation order. Under the hood, the FIFO queue locks messages in a group until they are successfully processed and deleted, preventing concurrent consumers from processing messages out of sequence. This approach is critical in scenarios like stock trading or multiplayer game state updates where message order directly affects correctness.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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
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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 an Amazon SQS FIFO queue to buffer messages before processing — Amazon API Gateway WebSockets does not guarantee ordered delivery of messages because WebSocket frames can arrive out of order over the network. Using an Amazon SQS FIFO queue as a buffer ensures that messages are processed in the exact order they are sent, preserving the sequence required for a real-time chat application. The FIFO queue provides first-in-first-out delivery and exactly-once processing, which solves the out-of-order issue without requiring custom sequencing logic.
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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