CKAD Application Deployment Practice Question
Which TWO of the following conditions must be met for a RollingUpdate to proceed?
⚠ Common exam trap
A common mix-up: candidates confuse the conditions for a RollingUpdate to proceed with the final state of the update, mistakenly thinking the old ReplicaSet must be scaled to zero or deleted, when in fact the update proceeds incrementally and the old ReplicaSet is only scaled down as new pods become ready.
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 new pod must pass its readiness probe
A is correct because during a RollingUpdate, the new pod must pass its readiness probe before the old pod is terminated. This ensures the new pod is capable of serving traffic, preventing service disruption. The readiness probe is checked by the kubelet, and only when it succeeds does the ReplicaSet controller proceed with the update.
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 new pod must pass its readiness probe
Why this is correct
During a rolling update, the Deployment controller creates a new ReplicaSet and scales it up. Before it proceeds to terminate old pods and scale up further, it must confirm that newly created pods are actually Ready by passing their readiness probes. If a new pod fails its readiness probe, the rollout stalls to protect availability, preventing traffic from being routed to unhealthy pods and avoiding cascading failures.
- ✓
The number of unavailable pods must not exceed maxUnavailable
Why this is correct
The deployment strategy's maxUnavailable setting defines the maximum number of Pods in the entire Deployment that can be unavailable during the rollout. The controller calculates the allowed number of unavailable pods (based on desired replicas and maxUnavailable, with a minimum of 1 when maxUnavailable is 0). It will not scale down old pods or scale up new pods if doing so would exceed this threshold, ensuring the Deployment has a guaranteed number of available replicas at all times.
- ✗
The new ReplicaSet must have the desired number of pods
Why it's wrong here
During a rolling update, the new ReplicaSet is scaled up incrementally, with the controller determining the exact scale based on the rollout's surge and availability constraints. The new ReplicaSet only reaches the full desired replica count at the very end of the rollout, after the old ReplicaSet has been fully scaled down. Requiring it to have the desired number from the start would defeat the purpose of rolling updates, which aim to maintain service availability by avoiding all-at-once pod replacement.
- ✗
The old ReplicaSet must be scaled to zero
Why it's wrong here
In a rolling update, the old ReplicaSet is scaled down gradually, in lockstep with the new ReplicaSet's scale-up, to keep the total number of pods within the surge and availability limits. It is never scaled to zero at the beginning; instead, its scale gradually decreases to zero only at the end of the rollout. Scaling it to zero immediately would be a recreate strategy, not a rolling update, and would cause downtime.
- ✗
The old ReplicaSet must be deleted
Why it's wrong here
Kubernetes retains the old ReplicaSet after a rollout completes, along with its pod template's revision history. This historical record enables instant rollback to a previous version by simply scaling down the current ReplicaSet and scaling up the old one. Deleting the old ReplicaSet would eliminate the ability to perform an easy rollback to that prior revision, so it is intentionally kept (subject to revisionHistoryLimit).
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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