CKAD Services and Networking Practice Question
You create a Service with the following manifest. What is the effect? service.yaml: apiVersion: v1 kind: Service metadata: name: ext-svc spec: type: ExternalName externalName: db.example.com
⚠ Common exam trap
It's easy for candidates to assume all Services must have a ClusterIP or select pods, but `ExternalName` is a special type that operates purely at the DNS level with no networking objects created.
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 service is a CNAME alias for db.example.com
A Service of type `ExternalName` creates a DNS CNAME record in the cluster's DNS (e.g., CoreDNS) that maps the Service name `ext-svc` to the external DNS name `db.example.com`. When a Pod resolves `ext-svc`, it receives the canonical name `db.example.com` directly, with no proxy, ClusterIP, or pod selection involved.
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 service is a CNAME alias for db.example.com
Why this is correct
An ExternalName service is a special Kubernetes service type that, instead of provisioning a ClusterIP or endpoints, writes a CNAME record into the cluster's DNS (CoreDNS) pointing to the external FQDN db.example.com. When a pod resolves the service's DNS name (e.g., my-service.default.svc.cluster.local), the DNS server returns a canonical answer directing the client to db.example.com directly. Because it is purely a DNS-level alias, no network proxy, selector, or load balancer is involved.
- ✗
The service gets a ClusterIP and forwards to db.example.com
Why it's wrong here
This is incorrect because ExternalName services never receive a ClusterIP by design. The spec has no `clusterIP` field applied; in fact, setting one is not allowed for ExternalName. Instead of forwarding traffic through a virtual IP and kube-proxy, the service simply instructs the cluster DNS to respond with the CNAME target db.example.com. Only normal ClusterIP services with selectors or manually defined endpoints get a virtual IP to route traffic to backend pods.
- ✗
The service creates a load balancer pointing to db.example.com
Why it's wrong here
A LoadBalancer service type requests a cloud-hosted load balancer from the underlying infrastructure provider and requires the service to have either selectors or pre-created endpoints to route to. An ExternalName service does not define any selectors or endpoints, and its spec contains the `externalName` field rather than type LoadBalancer. Consequently, no cloud load balancer is provisioned; the only effect is a DNS CNAME record that aliases the service to db.example.com. This option confuses the service types: ExternalName is purely a DNS alias, not a traffic-routing load balancer.
- ✗
The service selects pods with label app: ext
Why it's wrong here
ExternalName services explicitly do not use pod selectors because they are intended to point to resources outside the cluster. The manifest for an ExternalName service typically has no `selector` field at all; instead it declares an `externalName: db.example.com`. Even if a label `app: ext` happened to appear in the metadata (which is just descriptive), the service controller ignores it for ExternalName and does not build an Endpoints object. Pod label selection only applies to ClusterIP, NodePort, and LoadBalancer services, so selecting pods with that label is a separate mechanism entirely.
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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.