CKAD Application Observability and Maintenance Practice Question
You have a Deployment named 'api' with 3 replicas. You need to ensure that new pods are not added to the Service's endpoints until the application is ready to serve traffic. Which probe configuration should you add to the pod spec?
⚠ Common exam trap
A common mix-up: candidates confuse Liveness probes (which restart pods) with Readiness probes (which control traffic routing), or assume that a running pod is automatically considered ready for Service endpoints.
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
✓
Readiness probe
A Readiness probe is the correct choice because it controls whether a pod is added to a Service's endpoints. Kubernetes will only mark a pod as Ready when the probe succeeds, and only Ready pods receive traffic from the Service. This ensures new pods are not added until the application is ready to serve traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Readiness probe
Why this is correct
Readiness probe is the only mechanism that determines whether a pod should receive traffic from a Service. When the probe fails, the kubelet sets the pod's Ready condition to false, and the EndpointSlice controller removes that pod's IP from the Service's endpoints. For a Deployment with 3 replicas, this ensures only fully initialized and healthy-app-ready pods are behind the Service, preventing connection errors during startup or temporary stalls.
- ✗
No probe is needed; pods are automatically added when running
Why it's wrong here
Without a readiness probe, a pod is added to the Service endpoints as soon as it is Running and all its containers are started. This ignores the application's internal initialization phase, such as connecting to a database or warming caches, so traffic can be routed before the app can serve requests. The 'Running' status only reflects the container process being alive, not its ability to handle traffic; a readiness probe explicitly gates endpoint membership.
- ✗
Startup probe
Why it's wrong here
A startup probe is designed to give slow-starting containers extra time before liveness and readiness probes are executed; it reports whether the container has initialized its process. It does not directly affect the pod's Ready condition or the Service's endpoint list — that responsibility belongs solely to the readiness probe. Even if a startup probe succeeds, the pod remains unable to receive traffic until a separate readiness probe also passes.
- ✗
Liveness probe
Why it's wrong here
A liveness probe determines whether the container is healthy enough to keep running; if it fails, the kubelet kills and restarts the container. It does not influence Service endpoint membership by itself, because a container can pass its liveness probe while still being overwhelmed or not yet ready to serve requests. Unlike a readiness probe, liveness failure triggers a restart action rather than an endpoint removal, making it the wrong tool for controlling traffic routing.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CKAD practice question is part of Courseiva's free CNCF 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 CKAD exam.