CKAD Application Deployment Practice Question
You have a YAML file 'deploy.yaml' that defines a Deployment. Which command creates the Deployment if it does not exist, or updates it if it already exists?
⚠ Common exam trap
Many exam-takers confuse `kubectl create` (which only creates and errors on existing resources) with `kubectl apply` (which handles both create and update), or mistakenly think `kubectl replace` works like an upsert when it actually requires the resource to already exist.
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
✓
kubectl apply -f deploy.yaml
`kubectl apply -f deploy.yaml` uses declarative object configuration: it creates the Deployment if it doesn't exist, or performs a strategic merge patch to update it if it already exists. This is the standard command for managing Kubernetes resources with a desired-state file.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
kubectl replace -f deploy.yaml
Why it's wrong here
kubectl replace -f deploy.yaml performs a full object replacement: it sends the submitted YAML to the API server as a PUT request, overwriting the entire existing resource. If the Deployment does not already exist, replace fails with a NotFound error because it cannot replace a non-existent object. Even when the resource exists, replace is imperative and non-merge-aware, so any fields omitted from your YAML (e.g., annotations added by controllers) are dropped, unlike apply's three-way merge that preserves server-side defaults.
- ✗
kubectl patch -f deploy.yaml
Why it's wrong here
kubectl patch -f deploy.yaml is syntactically incomplete because kubectl patch expects a patch specification (JSON patch, merge patch, or strategic merge patch) as its argument, not a full Deployment manifest file. Even if you supplied a valid patch, this command would mutate the existing object in place based on the patch type, rather than reconciling the entire desired state defined in the YAML. Moreover, without a name and patch type (-p or --patch), the command would fail with an error, making it an incorrect, non-declarative choice for creating or updating a Deployment from a complete manifest.
- ✗
kubectl create -f deploy.yaml
Why it's wrong here
kubectl create -f deploy.yaml is an imperative command that submits a POST request to the API server to create a brand-new resource. If the Deployment already exists, the API server rejects the request with a Conflict error (409 AlreadyExists), so it cannot be used to update an existing Deployment. Even if the resource does not exist, create only establishes the initial resource and does not track or apply subsequent changes to the YAML file, so it does not provide the desired declarative update behavior.
- ✓
kubectl apply -f deploy.yaml
Why this is correct
kubectl apply -f deploy.yaml is the correct declarative command for this question. It sends a PATCH request using the apply semantics, which computes a three-way merge between the local YAML, the live object's current state, and the last-applied-configuration annotation (kubectl.kubernetes.io/last-applied-configuration). This creates the Deployment if it does not exist, or updates only the fields that differ from the desired state while preserving changes made by controllers or other actors. Because the question asks about a YAML deployment definition without any conditional like 'if it does not exist', apply is the idiomatic and safe way to ensure the desired state is enforced idempotently.
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