Using labels for service routing in Kubernetes - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select pods with the label app=frontend.

Kubernetes

selector:
  matchLabels:
    app: [1]

Drag options to blanks, or click blank then click option'

Acache

Bbackend

Cdatabase

Dfrontend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'backend' or other labels instead of 'frontend'.

The selector uses the label app=frontend to route traffic to frontend pods.

2fill in blank

medium

Complete the service selector to route traffic to pods with label tier=backend.

Kubernetes

selector:
  tier: [1]

Drag options to blanks, or click blank then click option'

Abackend

Bdatabase

Ccache

Dfrontend

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing 'frontend' with 'backend' label values.

The service selector uses tier=backend to route traffic to backend pods.

3fill in blank

hard

Fix the error in the selector to correctly route to pods with label env=production.

Kubernetes

selector:
  env: [1]

Drag options to blanks, or click blank then click option'

Astaging

Bproduction

Cdevelopment

Dtest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'staging' or other environment labels by mistake.

The selector must use env=production to route traffic to production pods.

4fill in blank

hard

Fill both blanks to route traffic to pods with labels app=api and version=v2.

Kubernetes

selector:
  app: [1]
  version: [2]

Drag options to blanks, or click blank then click option'

Aapi

Bv1

Cv2

Dweb

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing version values or app labels incorrectly.

The selector uses app=api and version=v2 to route traffic to the correct pods.

5fill in blank

hard

Fill all three blanks to create a selector for pods with labels role=frontend, env=prod, and track=stable.

Kubernetes

selector:
  role: [1]
  env: [2]
  track: [3]

Drag options to blanks, or click blank then click option'

Afrontend

Bprod

Cstable

Ddev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'dev' instead of 'prod' or mixing labels.

The selector uses role=frontend, env=prod, and track=stable to route traffic correctly.

Practice

1. What is the main purpose of using labels in Kubernetes service routing?

easy

A. To connect services to the correct pods

B. To store pod logs

C. To define pod resource limits

D. To schedule pods on specific nodes

Solution

1. Step 1: Understand labels role

   Labels are key-value pairs attached to pods to identify them.

2. Step 2: Connect services using selectors

   Services use selectors to find pods with matching labels for routing traffic.

3. Final Answer:

   To connect services to the correct pods -> Option A

4. Quick Check:

   Labels link services and pods = D [OK]

Hint: Labels identify pods for services to route traffic [OK]

Common Mistakes:

• Confusing labels with resource limits
• Thinking labels store logs
• Assuming labels control pod scheduling

2. Which of the following is the correct syntax to select pods with label app=frontend in a Service YAML?

easy

A. selector:
app: frontend

B. selector:
app = frontend

C. selector:
app: 'frontend'
version: 'v1'

D. selector:
- app: frontend

Solution

1. Step 1: Check YAML selector syntax

   Selectors use key: value pairs without '=' sign or list format.

2. Step 2: Validate options

   selector: app: frontend uses correct key: value syntax. selector: app = frontend uses '=' which is invalid. selector: app: 'frontend' version: 'v1' adds extra label, which is valid but not asked. selector: - app: frontend uses list format which is invalid for selector.

3. Final Answer:

   selector: app: frontend -> Option A

4. Quick Check:

   Selector uses key: value, no '=' or list [OK]

Hint: Use key: value pairs for selectors, no '=' or lists [OK]

Common Mistakes:

• Using '=' instead of ':' in YAML
• Writing selectors as lists
• Adding extra labels not requested

3. Given this Service YAML snippet:

selector:
  app: backend
  tier: api

Which pods will this Service route traffic to?

medium

A. Pods labeled only with app=backend

B. Pods labeled with either app=backend or tier=api

C. Pods labeled with both app=backend and tier=api

D. Pods labeled only with tier=api

Solution

1. Step 1: Understand selector matching

   Selectors match pods that have all specified labels (AND logic).

2. Step 2: Apply to given labels

   Pods must have both app=backend and tier=api labels to be selected.

3. Final Answer:

   Pods labeled with both app=backend and tier=api -> Option C

4. Quick Check:

   Selector matches all labels (AND) = A [OK]

Hint: Selectors match pods with all labels, not just one [OK]

Common Mistakes:

• Assuming selector matches any label (OR logic)
• Ignoring one of the labels in selector
• Confusing selector with pod annotations

4. You created a Service with selector:

selector:
  app: web
  env: prod

But traffic is not reaching pods. What is the most likely cause?

medium

A. Pods are not running on the same node

B. Service type is not LoadBalancer

C. Service port is missing

D. Pods do not have both labels app=web and env=prod

Solution

1. Step 1: Check label matching

   Service routes only to pods matching all selector labels.

2. Step 2: Identify common mismatch

   If pods lack either label, service finds no endpoints, so no traffic flows.

3. Final Answer:

   Pods do not have both labels app=web and env=prod -> Option D

4. Quick Check:

   Missing labels cause no pod selection = C [OK]

Hint: Verify pods have all selector labels to receive traffic [OK]

Common Mistakes:

• Blaming service type instead of labels
• Assuming node location affects routing
• Ignoring missing service port errors

5. You want to update your app without downtime. You have pods labeled app=frontend, version=v1. You deploy new pods with app=frontend, version=v2. How should you configure the Service selector to route traffic to both versions during rollout?

hard

A. Use selector: version=v2 only

B. Use selector: app=frontend only

C. Use selector: app=frontend and version=v2

D. Use selector: app=frontend and version=v1

Solution

1. Step 1: Understand rolling update strategy

   To route traffic to both old and new pods, selector must match both versions.

2. Step 2: Choose selector that matches both versions

   Selector with only app=frontend matches all pods regardless of version label.

3. Step 3: Avoid version-specific selectors

   Selectors with version=v1 or version=v2 exclude the other version, causing downtime.

4. Final Answer:

   Use selector: app=frontend only -> Option B

5. Quick Check:

   Selector matches all versions for smooth rollout = B [OK]

Hint: Use broad selector to include all versions during rollout [OK]

Common Mistakes:

• Selecting only new version pods causing downtime
• Selecting only old version pods ignoring new pods
• Using multiple selectors that exclude pods