- A
Application Load Balancer
Correct. ALB supports WebSocket protocol natively and provides sticky sessions (session affinity) using cookies or source IP. It operates at Layer 7, making it ideal for real-time chat applications that require persistent connections and application-aware routing.
- B
Network Load Balancer
Why wrong: Incorrect. While NLB can forward WebSocket traffic at Layer 4 (TCP), it does not offer native WebSocket support or application-layer features like cookie-based sticky sessions. NLB is designed for ultra-low latency and extreme performance, not for application-level session management.
- C
Classic Load Balancer
Why wrong: Incorrect. Classic Load Balancer is a legacy service that works at Layer 4 and Layer 7, but it does not support the WebSocket protocol. Additionally, it lacks the advanced features of ALB and is not recommended for new applications.
- D
Amazon Route 53
Why wrong: Incorrect. Amazon Route 53 is a Domain Name System (DNS) service. It can direct traffic to endpoints using routing policies (e.g., latency-based) but does not function as a load balancer. It cannot maintain sticky sessions or handle WebSocket connections directly.
CLF-C02 Cloud Technology and Services Practice Question
This CLF-C02 practice question tests your understanding of cloud technology and 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 company is building a real-time chat application that relies on long-lived WebSocket connections between clients and backend servers. The application runs on Amazon EC2 instances across multiple Availability Zones. The company needs a load balancer that can distribute incoming WebSocket traffic while preserving the connection and supporting sticky sessions. Which AWS load balancing solution should the company use?
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
Application Load Balancer
The Application Load Balancer (ALB) supports WebSocket connections natively at the application layer (Layer 7) and can maintain persistent connections via its built-in sticky session (session affinity) feature, which uses a cookie to bind a client to a specific target for the duration of the WebSocket session. This makes ALB the correct choice for a real-time chat application requiring long-lived WebSocket connections and sticky sessions across multiple Availability Zones.
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.
- ✓
Application Load Balancer
Why this is correct
Correct. ALB supports WebSocket protocol natively and provides sticky sessions (session affinity) using cookies or source IP. It operates at Layer 7, making it ideal for real-time chat applications that require persistent connections and application-aware routing.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Network Load Balancer
Why it's wrong here
Incorrect. While NLB can forward WebSocket traffic at Layer 4 (TCP), it does not offer native WebSocket support or application-layer features like cookie-based sticky sessions. NLB is designed for ultra-low latency and extreme performance, not for application-level session management.
- ✗
Classic Load Balancer
Why it's wrong here
Incorrect. Classic Load Balancer is a legacy service that works at Layer 4 and Layer 7, but it does not support the WebSocket protocol. Additionally, it lacks the advanced features of ALB and is not recommended for new applications.
When this WOULD be correct
A Classic Load Balancer would be correct for distributing HTTP/HTTPS traffic for a legacy web application that requires simple sticky sessions (duration-based) and does not need WebSocket support, advanced routing, or integration with modern AWS services like AWS WAF or Lambda functions.
- ✗
Amazon Route 53
Why it's wrong here
Incorrect. Amazon Route 53 is a Domain Name System (DNS) service. It can direct traffic to endpoints using routing policies (e.g., latency-based) but does not function as a load balancer. It cannot maintain sticky sessions or handle WebSocket connections directly.
When this WOULD be correct
Route 53 would be correct in a scenario where the question asks for a service to route users to the nearest application endpoint based on latency or geographic location, without requiring connection-level load balancing or sticky sessions.
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 CLF-C02 exam frequently reuses these exact scenarios with slightly different constraints.
✓Application Load BalancerCorrect answer▾
Why this is correct
Correct. ALB supports WebSocket protocol natively and provides sticky sessions (session affinity) using cookies or source IP. It operates at Layer 7, making it ideal for real-time chat applications that require persistent connections and application-aware routing.
✗Network Load BalancerWrong answer — click to see why▾
Why this is wrong here
Network Load Balancer operates at Layer 4 and does not support WebSocket protocol or sticky sessions based on application-level cookies, which are required for the real-time chat application.
★ When this WOULD be the correct answer
A company needs to handle millions of requests per second with ultra-low latency, using TCP or UDP traffic, and requires static IP addresses for whitelisting. The application does not need HTTP/WebSocket features or sticky sessions.
Why candidates choose this
Candidates may confuse NLB's ability to preserve connections (via TCP) with WebSocket support, or assume that any modern load balancer handles WebSocket, overlooking that ALB is specifically designed for Layer 7 protocols like WebSocket.
✗Classic Load BalancerWrong answer — click to see why▾
Why this is wrong here
Classic Load Balancer does not support WebSocket connections or sticky sessions based on application-level cookies; it only supports TCP and HTTP/HTTPS with basic sticky sessions using duration-based cookies, which are insufficient for long-lived WebSocket connections.
★ When this WOULD be the correct answer
A Classic Load Balancer would be correct for distributing HTTP/HTTPS traffic for a legacy web application that requires simple sticky sessions (duration-based) and does not need WebSocket support, advanced routing, or integration with modern AWS services like AWS WAF or Lambda functions.
Why candidates choose this
Candidates may recall that Classic Load Balancer supports sticky sessions and assume it works for WebSocket connections, not realizing that WebSocket support requires the Application Load Balancer's native WebSocket protocol handling and application-level stickiness.
✗Amazon Route 53Wrong answer — click to see why▾
Why this is wrong here
Amazon Route 53 is a DNS web service, not a load balancer. It cannot distribute incoming WebSocket traffic or preserve connections with sticky sessions.
★ When this WOULD be the correct answer
Route 53 would be correct in a scenario where the question asks for a service to route users to the nearest application endpoint based on latency or geographic location, without requiring connection-level load balancing or sticky sessions.
Why candidates choose this
Candidates may confuse Route 53's traffic flow features (like latency-based routing) with actual load balancing, or think DNS-level routing can handle WebSocket connections.
Analysis generated from the official CLF-C02blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume Network Load Balancer is the only option for WebSocket because it operates at Layer 4 and handles long-lived TCP connections, but they overlook that ALB explicitly supports WebSocket at Layer 7 and provides the required sticky session feature via cookies, which NLB lacks.
Detailed technical explanation
How to think about this question
Under the hood, ALB handles WebSocket upgrades by intercepting the HTTP Upgrade header (e.g., Upgrade: websocket) and then maintaining the TCP connection as a bidirectional tunnel between the client and the target EC2 instance, without inspecting further payload. The sticky session feature in ALB uses a generated cookie (AWSALB) that is set on the initial HTTP handshake, ensuring subsequent WebSocket frames are routed to the same instance even if the connection is re-established after a brief interruption.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
What to study next
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FAQ
Questions learners often ask
What does this CLF-C02 question test?
Cloud Technology and Services — This question tests Cloud Technology and Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Application Load Balancer — The Application Load Balancer (ALB) supports WebSocket connections natively at the application layer (Layer 7) and can maintain persistent connections via its built-in sticky session (session affinity) feature, which uses a cookie to bind a client to a specific target for the duration of the WebSocket session. This makes ALB the correct choice for a real-time chat application requiring long-lived WebSocket connections and sticky sessions across multiple Availability Zones.
What should I do if I get this CLF-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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Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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Last reviewed: Jun 11, 2026
This CLF-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 CLF-C02 exam.
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