Using labels for service routing in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Service routing with label selectors

Given the following Kubernetes service and pod labels, what pods will the service route traffic to?

Kubernetes

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: web
    tier: frontend
  ports:
  - protocol: TCP
    port: 80
    targetPort: 8080

Pods:
- pod1 labels: {app: web, tier: frontend}
- pod2 labels: {app: web, tier: backend}
- pod3 labels: {app: api, tier: frontend}

A pod1 only

B pod1 and pod2

C pod1 and pod3

D pod2 and pod3

💡 Hint

The service selector matches pods with both labels 'app: web' and 'tier: frontend'.

The service selector requires both labels to match. Only pod1 has both 'app: web' and 'tier: frontend'. Pod2 misses 'tier: frontend' and pod3 misses 'app: web'.

🧠 Conceptual

intermediate

Label importance in service routing

Why are labels important for Kubernetes service routing?

A They store the service's IP address

B They configure the service's port numbers

C They specify the container image version

D They define which pods receive traffic from the service

💡 Hint

Think about how a service knows which pods to send traffic to.

Labels act as selectors that tell the service which pods to route traffic to based on matching labels.

❓ Configuration

advanced

Correct label selector syntax

Which of the following service selector configurations correctly selects pods with label 'env=prod' and 'version=v2'?

Kubernetes

apiVersion: v1
kind: Service
metadata:
  name: example-service
spec:
  selector:

A

- env: prod
- version: v2

B env=prod, version=v2

C

env: prod
version: v2

D env: 'prod', version: 'v2'

💡 Hint

Look for the correct YAML key-value mapping under selector.

The selector field expects a map of key-value pairs. Option C correctly uses YAML mapping syntax. Option C is invalid syntax. Option C is a list, which is incorrect. Option C uses commas inside a map which is invalid YAML.

❓ Troubleshoot

advanced

Service routes no pods despite matching labels

A service selector is set to 'app: backend'. Pods have label 'app: backend'. However, the service routes no traffic. What is the most likely cause?

A Pods have the label but are not running

B Pods are not in the same namespace as the service

C Service port and pod targetPort do not match

D Service type is ClusterIP instead of NodePort

💡 Hint

Check pod status and readiness.

Even if labels match, if pods are not running or not ready, the service will not route traffic to them.

🔀 Workflow

expert

Label-based canary deployment routing

You want to route 10% of traffic to pods labeled 'version: canary' and 90% to 'version: stable' using Kubernetes services. Which approach achieves this?

A Change pod labels dynamically to switch 10% of pods to 'version: canary'

B Create two services with selectors for each version and use an Ingress or external load balancer to split traffic by weight

C Label all pods with both 'version: canary' and 'version: stable' and use one service

D Use a single service with selector 'version: canary, stable' to route traffic proportionally

💡 Hint

Kubernetes services do not support weighted routing by themselves.

Kubernetes services select pods by labels but do not support traffic splitting by weight. Creating separate services and using an Ingress or external load balancer to split traffic achieves weighted routing.