Using labels for service routing in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

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What is a label in Kubernetes?

A label is a key-value pair attached to Kubernetes objects like pods. It helps identify and organize resources for selection and routing.

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How do labels help with service routing in Kubernetes?

Labels allow services to select and route traffic only to pods with matching labels, enabling targeted communication between components.

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What is a selector in a Kubernetes Service?

A selector is a query that matches pods with specific labels. The service routes traffic to all pods matching this selector.

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Example: How to label a pod with app=frontend?

In the pod YAML, under metadata, add: <br> labels:<br> app: frontend

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How does a Kubernetes Service use labels to route traffic?

The service uses a selector to find pods with matching labels and sends network requests only to those pods.

What does a Kubernetes Service selector do?

A Creates new pods automatically

B Deletes pods without labels

C Matches pods with specific labels to route traffic

D Changes pod labels dynamically

A selector matches pods with labels so the service knows where to send traffic.

Which of these is a valid label format?

A app/frontend

B app frontend

C app=frontend

D app:frontend

Labels use key:value format in YAML, like app: frontend.

If a service selector is 'app=backend', which pods receive traffic?

A All pods in the cluster

B Pods labeled with app=backend

C Pods without labels

D Pods labeled with app=frontend

Only pods with the label app=backend get traffic from that service.

Can a pod have multiple labels?

A Yes, pods can have many labels

B No, only one label is allowed

C Only if the pod is running

D Only for system pods

Pods can have many labels to describe different attributes.

What happens if no pods match a service selector?

A The service has no endpoints and traffic fails

B The service routes traffic to all pods

C The service creates new pods automatically

D The service ignores the selector

If no pods match, the service has no endpoints and cannot route traffic.

Explain how labels and selectors work together to route traffic in Kubernetes services.

Think about how a service finds the right pods to send requests.

Describe how you would label a pod and create a service to route traffic to it.

Consider the YAML structure for both pod and service.