Scaling Deployments in Kubernetes - Mini Project: Build & Apply

Scaling Deployments in Kubernetes

📖 Scenario: You are managing a web application running on Kubernetes. The application needs to handle more users during peak hours. To do this, you will learn how to scale the number of pods in a deployment.

🎯 Goal: Learn how to create a Kubernetes deployment and scale it up by increasing the number of pods.

📋 What You'll Learn

Create a deployment YAML file with a specific name and image

Add a replicas field to set the number of pods

Use kubectl commands to apply the deployment and scale it

Verify the number of pods running matches the desired count

💡 Why This Matters

🌍 Real World

Scaling deployments is essential to handle varying user loads in real applications. It helps maintain performance and availability.

💼 Career

Kubernetes deployment scaling is a fundamental skill for DevOps engineers and site reliability engineers managing cloud-native applications.

1

Create a Deployment YAML file

Create a file named deployment.yaml with a Kubernetes deployment named webapp using the image nginx:1.21. Set the initial number of replicas to 1. Include the required fields: apiVersion, kind, metadata, and spec with replicas and template containing containers with the image.

Kubernetes

# Write the deployment.yaml content here
# Your code here

Hint

Remember to include replicas: 1 under spec and set the container image to nginx:1.21.

2

Apply the Deployment and Check Pods

Use the command kubectl apply -f deployment.yaml to create the deployment. Then use kubectl get pods -l app=webapp to list the pods with the label app=webapp. Write the exact commands below.

Kubernetes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp
spec:
  replicas: 1
  selector:
    matchLabels:
      app: webapp
  template:
    metadata:
      labels:
        app: webapp
    spec:
      containers:
      - name: nginx-container
        image: nginx:1.21

# Apply the deployment
# Your code here

# List pods with label app=webapp
# Your code here

Hint

Use kubectl apply -f deployment.yaml to create the deployment and kubectl get pods -l app=webapp to see the pods.

3

Scale the Deployment to 3 Replicas

Update the deployment.yaml file to set replicas to 3. Then use the command kubectl apply -f deployment.yaml again to apply the change.

Kubernetes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp
spec:
  replicas: 3  # Change replicas to 3
  selector:
    matchLabels:
      app: webapp
  template:
    metadata:
      labels:
        app: webapp
    spec:
      containers:
      - name: nginx-container
        image: nginx:1.21

# Apply the updated deployment
# Your code here

Hint

Change the replicas field to 3 and apply the deployment again.

4

Verify the Number of Pods Running

Run the command kubectl get pods -l app=webapp --no-headers | wc -l to count the number of pods running with label app=webapp. Then print the number using echo in the format: Pods running: 3.

Kubernetes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp
spec:
  replicas: 3
  selector:
    matchLabels:
      app: webapp
  template:
    metadata:
      labels:
        app: webapp
    spec:
      containers:
      - name: nginx-container
        image: nginx:1.21

kubectl apply -f deployment.yaml

# Count pods and print the result
# Your code here

Hint

Use command substitution to count pods and then print with echo.

Practice

1. What does scaling a Kubernetes deployment do?

easy

A. Changes the number of running copies (pods) of the app

B. Updates the app's source code automatically

C. Deletes the deployment from the cluster

D. Changes the app's network settings

Solution

1. Step 1: Understand the purpose of scaling

   Scaling means adjusting how many copies of an app run to handle load or save resources.

2. Step 2: Identify what scaling affects

   Scaling changes the number of pods, which are running instances of the app.

3. Final Answer:

   Changes the number of running copies (pods) of the app -> Option A

4. Quick Check:

   Scaling = Change pod count [OK]

Hint: Scaling means changing pod count, not code or network [OK]

Common Mistakes:

• Thinking scaling updates app code
• Confusing scaling with deleting deployments
• Assuming scaling changes network settings

2. Which is the correct command to scale a deployment named webapp to 5 replicas?

easy

A. kubectl scale pods webapp --count=5

B. kubectl update deployment webapp --replicas 5

C. kubectl set replicas webapp 5

D. kubectl scale deployment webapp --replicas=5

Solution

1. Step 1: Recall the correct kubectl scale syntax

   The command to scale is kubectl scale deployment [name] --replicas=[number].

2. Step 2: Match the command to the options

   kubectl scale deployment webapp --replicas=5 matches the correct syntax exactly for deployment webapp to 5 replicas.

3. Final Answer:

   kubectl scale deployment webapp --replicas=5 -> Option D

4. Quick Check:

   Correct scale syntax = kubectl scale deployment webapp --replicas=5 [OK]

Hint: Use 'kubectl scale deployment NAME --replicas=N' exactly [OK]

Common Mistakes:

• Using 'pods' instead of 'deployment'
• Wrong flag like --count instead of --replicas
• Using 'kubectl update' which is invalid for scaling

3. Given this command:
kubectl scale deployment frontend --replicas=3
What will be the number of pods running for the frontend deployment after execution?

medium

A. 0

B. 1

C. 3

D. Depends on cluster resources

Solution

1. Step 1: Understand the scale command effect

   The command sets the number of replicas (pods) to 3 explicitly.

2. Step 2: Determine the pod count after scaling

   After running, Kubernetes will ensure exactly 3 pods for the frontend deployment.

3. Final Answer:

   3 -> Option C

4. Quick Check:

   --replicas=3 means 3 pods [OK]

Hint: Replicas number = pods count after scaling [OK]

Common Mistakes:

• Assuming pods stay at 1 by default
• Thinking scaling depends on cluster resources
• Confusing replicas with CPU or memory

4. You run kubectl scale deployment backend --replicas=two but get an error. What is the problem?

medium

A. The deployment name 'backend' is invalid

B. The replicas value must be a number, not a word

C. The command should use 'kubectl update' instead

D. You need to add --force flag to scale

Solution

1. Step 1: Check the replicas argument type

   The replicas flag requires a numeric value, not a word like 'two'.

2. Step 2: Identify the cause of the error

   Using 'two' causes a syntax error because Kubernetes expects an integer.

3. Final Answer:

   The replicas value must be a number, not a word -> Option B

4. Quick Check:

   Replicas must be numeric [OK]

Hint: Replicas must be a number, not text [OK]

Common Mistakes:

• Using words instead of numbers for replicas
• Thinking deployment name is invalid without checking
• Trying to use 'kubectl update' for scaling

5. You want to scale a deployment named api-server from 2 to 10 replicas but only 6 nodes are available in your cluster. What will happen after running kubectl scale deployment api-server --replicas=10?

hard

A. Only 6 pods will run because of node limits, others stay pending

B. The deployment will scale to 2 pods automatically

C. The command will fail with an error about node count

D. Kubernetes will create 10 pods regardless of node count

Solution

1. Step 1: Understand Kubernetes scheduling with limited nodes

   Kubernetes tries to run all requested pods but can only schedule as many as fit on available nodes.

2. Step 2: Predict pod status with 10 replicas but 6 nodes

   Only 6 pods will be scheduled and running; the other 4 pods remain pending until resources free up.

3. Final Answer:

   Only 6 pods will run because of node limits, others stay pending -> Option A

4. Quick Check:

   Pods limited by nodes = pending pods [OK]

Hint: Pods > nodes means some pods stay pending [OK]

Common Mistakes:

• Assuming all pods run regardless of nodes
• Expecting command to fail on node shortage
• Thinking deployment scales down automatically