Question 269 of 505

Application Deployment and Security →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the deployment has hostPort: 8080 specified, causing a port conflict when multiple replicas are scheduled on the same node. This is correct because the CrashLoopBackOff error with “bind: address already in use” occurs when a container process tries to bind to a port that is already occupied on the host network namespace. When hostPort is set, Kubernetes maps the container port directly to the node’s IP, so if two pods land on the same node, both attempt to claim port 8080, leading to the failure. On the Cisco DevNet Associate 200-901 exam, this scenario tests your understanding of Kubernetes networking and common misconfigurations with hostPort, often appearing as a trap where candidates overlook replica scheduling. A useful memory tip: “hostPort = host conflict” — if you see multiple replicas and a bind error, suspect hostPort is locking the port on the node.

200-901 Application Deployment and Security Practice Question

This 200-901 practice question tests your understanding of application deployment and security. 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 network engineer is troubleshooting a Kubernetes deployment where pods are failing to start with the error 'CrashLoopBackOff'. The pod log shows 'bind: address already in use'. The deployment runs multiple replicas of a container that listens on port 8080. What is the most likely cause?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1hardmultiple choice

Full question →

A
The container is attempting to bind to a privileged port without the necessary capabilities.
Why wrong: Port 8080 is not privileged (privileged ports are below 1024).
B
The deployment has hostPort: 8080 specified, causing port conflict when multiple replicas are scheduled on the same node.
hostPort reserves the port on the host node, so only one pod per node can use it. With multiple replicas, subsequent pods fail with address in use.
C
The service is using NodePort and the node port is already in use.
Why wrong: NodePort is a service type; the error occurs at the container level, not the service level.
D
Multiple containers in the same pod are trying to bind to the same port.
Why wrong: Containers in a pod share the same network namespace; they cannot bind to the same port, but the error would occur at pod creation, not as CrashLoopBackOff after start.

Full breakdown with real-world context →

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

✓

The deployment has hostPort: 8080 specified, causing port conflict when multiple replicas are scheduled on the same node.

The 'bind: address already in use' error indicates that the container's process cannot bind to port 8080 because it is already occupied. When `hostPort: 8080` is specified in the pod spec, Kubernetes instructs the container runtime to map the container port to the same port on the node's network namespace. If multiple replicas of the deployment are scheduled on the same node, each pod attempts to bind to port 8080 on the host, causing a conflict and the CrashLoopBackOff state. This is a common misconfiguration when using hostPort without ensuring that replicas are spread across different nodes.

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.

✗
The container is attempting to bind to a privileged port without the necessary capabilities.
Why it's wrong here
Port 8080 is not privileged (privileged ports are below 1024).
✓
The deployment has hostPort: 8080 specified, causing port conflict when multiple replicas are scheduled on the same node.
Why this is correct
hostPort reserves the port on the host node, so only one pod per node can use it. With multiple replicas, subsequent pods fail with address in use.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The service is using NodePort and the node port is already in use.
Why it's wrong here
NodePort is a service type; the error occurs at the container level, not the service level.
✗
Multiple containers in the same pod are trying to bind to the same port.
Why it's wrong here
Containers in a pod share the same network namespace; they cannot bind to the same port, but the error would occur at pod creation, not as CrashLoopBackOff after start.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between hostPort (which binds to the node's IP) and containerPort (which is informational), leading candidates to overlook that hostPort causes direct port conflicts on the same node.

Detailed technical explanation

How to think about this question

When `hostPort` is set, the kubelet uses the container runtime (e.g., Docker or containerd) to publish the container port to the host network interface. This is implemented via iptables rules or port mapping in the container's network namespace. In a real-world scenario, using hostPort is often discouraged because it limits pod scheduling to one pod per node for that port, reducing scalability; instead, a Service with ClusterIP or NodePort should be used to route traffic without host-level port contention.

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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 200-901 question test?

Application Deployment and Security — This question tests Application Deployment and Security — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The deployment has hostPort: 8080 specified, causing port conflict when multiple replicas are scheduled on the same node. — The 'bind: address already in use' error indicates that the container's process cannot bind to port 8080 because it is already occupied. When `hostPort: 8080` is specified in the pod spec, Kubernetes instructs the container runtime to map the container port to the same port on the node's network namespace. If multiple replicas of the deployment are scheduled on the same node, each pod attempts to bind to port 8080 on the host, causing a conflict and the CrashLoopBackOff state. This is a common misconfiguration when using hostPort without ensuring that replicas are spread across different nodes.

What should I do if I get this 200-901 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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