ReplicaSet definition in Kubernetes - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the kind of Kubernetes object.

Kubernetes

apiVersion: apps/v1
kind: [1]
metadata:
  name: my-replicaset

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

APod

BDeployment

CReplicaSet

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Using Deployment instead of ReplicaSet

Using Pod or Service as kind

The kind field specifies the type of Kubernetes object. For a ReplicaSet, it must be ReplicaSet.

2fill in blank

medium

Complete the code to set the number of pod replicas.

Kubernetes

spec:
  replicas: [1]

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

A0

B-1

Cabc

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Setting replicas to zero or negative numbers

Using non-numeric values

The replicas field sets how many pod copies the ReplicaSet should maintain. It must be a positive integer like 3.

3fill in blank

hard

Fix the error in the selector field to match the pod labels.

Kubernetes

spec:
  selector:
    matchLabels:
      app: [1]

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

Afrontend

Bbackend

Cdatabase

Dcache

Attempts:

3 left

💡 Hint

Common Mistakes

Using a label that does not match pod labels

Typos in label values

The selector must match the labels of the pods the ReplicaSet manages. Here, the pods have label app: frontend.

4fill in blank

hard

Fill both blanks to complete the pod template metadata and container name.

Kubernetes

spec:
  template:
    metadata:
      labels:
        app: [1]
    spec:
      containers:
      - name: [2]
        image: nginx:latest

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

Afrontend

Bbackend

Cnginx

Dredis

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatch between labels and selector

Using container names that don't match the image

The pod template labels must match the selector labels. The container name is usually the application or image name, here nginx.

5fill in blank

hard

Fill all three blanks to complete the ReplicaSet spec with replicas, selector, and pod labels.

Kubernetes

spec:
  replicas: [1]
  selector:
    matchLabels:
      app: [2]
  template:
    metadata:
      labels:
        app: [3]

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

Afrontend

B3

Dbackend

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatch between selector and pod labels

Using non-numeric replicas

The replicas is set to 3. The selector and pod labels must match and are both frontend.

Practice

1. What is the main purpose of a ReplicaSet in Kubernetes?

easy

A. To manage network policies between pods

B. To store persistent data for pods

C. To ensure a specified number of pod replicas are running at all times

D. To schedule pods on specific nodes

Solution

1. Step 1: Understand ReplicaSet role

   A ReplicaSet's job is to keep a stable set of pod replicas running.

2. Step 2: Compare options with ReplicaSet function

   Only To ensure a specified number of pod replicas are running at all times describes maintaining pod replicas, which is the ReplicaSet's purpose.

3. Final Answer:

   To ensure a specified number of pod replicas are running at all times -> Option C

4. Quick Check:

   ReplicaSet manages pod count = A [OK]

Hint: ReplicaSet = keeps pods running in set number [OK]

Common Mistakes:

• Confusing ReplicaSet with PersistentVolume
• Thinking ReplicaSet manages network policies
• Mixing ReplicaSet with pod scheduling

2. Which of the following is the correct minimal YAML snippet to define a ReplicaSet with 3 replicas?

easy

A. apiVersion: apps/v1\nkind: ReplicaSet\nmetadata:\n name: my-rs\nspec:\n replicas: 3\n selector:\n matchLabels:\n app: myapp\n template:\n metadata:\n labels:\n app: myapp\n spec:\n containers:\n - name: nginx\n image: nginx

B. apiVersion: v1\nkind: ReplicaSet\nmetadata:\n name: my-rs\nspec:\n replicas: 3\n selector:\n app: myapp\n template:\n metadata:\n labels:\n app: myapp\n spec:\n containers:\n - name: nginx\n image: nginx

C. apiVersion: apps/v1\nkind: ReplicaSet\nmetadata:\n name: my-rs\nspec:\n replicas: three\n selector:\n matchLabels:\n app: myapp\n template:\n metadata:\n labels:\n app: myapp\n spec:\n containers:\n - name: nginx\n image: nginx

D. apiVersion: apps/v1\nkind: ReplicaSet\nmetadata:\n name: my-rs\nspec:\n replicas: 3\n selector:\n matchLabels:\n app: myapp\n template:\n metadata:\n labels:\n app: otherapp\n spec:\n containers:\n - name: nginx\n image: nginx

Solution

1. Step 1: Check apiVersion and kind

   ReplicaSet requires apiVersion: apps/v1 and kind: ReplicaSet. The option with apiVersion: v1 is invalid.

2. Step 2: Validate replicas and selector-template match

   Replicas must be an integer like 3, not string 'three'. Selector labels must match template labels exactly (one option has template app: otherapp mismatch). Only one option has all correct: apps/v1, replicas: 3, matching labels with proper structure.

3. Final Answer:

   Correct YAML with apiVersion apps/v1, replicas: 3, matching selector and template labels -> Option A

4. Quick Check:

   YAML syntax + matching labels = D [OK]

Hint: Match selector labels exactly with template labels [OK]

Common Mistakes:

• Using wrong apiVersion
• Setting replicas as string instead of number
• Mismatching selector and template labels

3. Given this ReplicaSet YAML snippet, what will be the number of pods running after applying it?

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: test-rs
spec:
  replicas: 2
  selector:
    matchLabels:
      app: test
  template:
    metadata:
      labels:
        app: test
    spec:
      containers:
      - name: busybox
        image: busybox
        command: ['sleep', '3600']

medium

A. 3 pods

B. 1 pod

C. 0 pods

D. 2 pods

Solution

1. Step 1: Check replicas field

   The spec.replicas is set to 2, so Kubernetes will try to run 2 pods matching the selector.

2. Step 2: Confirm selector and template labels match

   Selector matches label app: test, and template labels also have app: test, so pods will be created.

3. Final Answer:

   2 pods -> Option D

4. Quick Check:

   replicas = 2 pods running [OK]

Hint: replicas number = pods running if labels match [OK]

Common Mistakes:

• Ignoring label selector and template label matching
• Assuming pods run without matching labels
• Confusing replicas with container count

4. You applied a ReplicaSet YAML but no pods are created. Which of these is the most likely cause?

medium

A. The replicas field is set to 0

B. The selector labels do not match the pod template labels

C. The container image name is misspelled

D. The ReplicaSet name is missing

Solution

1. Step 1: Understand pod creation depends on selector matching template labels

   If selector labels don't match pod template labels, ReplicaSet won't manage any pods.

2. Step 2: Evaluate other options

   Replicas 0 means no pods, but question says pods expected. Misspelled image causes pod crash, not zero pods. Name missing causes YAML error, not silent no pods.

3. Final Answer:

   The selector labels do not match the pod template labels -> Option B

4. Quick Check:

   Selector-template label mismatch = no pods [OK]

Hint: Selector and template labels must match exactly [OK]

Common Mistakes:

• Assuming image typo prevents pod creation
• Ignoring selector-template label mismatch
• Thinking ReplicaSet name is optional

5. You want to update a ReplicaSet to increase replicas from 2 to 5 but keep the same pods running without downtime. What is the best approach?

hard

A. Scale the ReplicaSet using kubectl scale command to 5 replicas

B. Delete the ReplicaSet and create a new one with replicas: 5

C. Edit the ReplicaSet YAML to set replicas: 5 and apply it

D. Change the pod template labels to new values and apply

Solution

1. Step 1: Understand scaling ReplicaSet

   Scaling with kubectl scale updates replicas live without downtime.

2. Step 2: Evaluate other options

   Editing YAML and applying works but less safe than scale command. Deleting ReplicaSet causes downtime. Changing labels breaks pod matching.

3. Final Answer:

   Scale the ReplicaSet using kubectl scale command to 5 replicas -> Option A

4. Quick Check:

   Use kubectl scale for live replica changes [OK]

Hint: Use kubectl scale to change replicas live [OK]

Common Mistakes:

• Deleting ReplicaSet causes downtime
• Changing labels breaks pod matching
• Editing YAML directly risks errors