Creating Deployments with YAML in Kubernetes - Try It Yourself

Creating Deployments with YAML

📖 Scenario: You are working as a DevOps engineer. Your team needs to deploy a simple web application on Kubernetes. You will create a Deployment YAML file step-by-step to manage the application pods.

🎯 Goal: Build a Kubernetes Deployment YAML file that defines a Deployment named webapp-deployment running 3 replicas of the nginx:1.21 container.

📋 What You'll Learn

Create a Deployment YAML with apiVersion, kind, and metadata

Add a spec section with replicas and selector

Define the pod template with container name and image

Output the complete YAML content

💡 Why This Matters

🌍 Real World

Kubernetes Deployments are used to manage and scale containerized applications in production environments.

💼 Career

Understanding how to write Deployment YAML files is essential for DevOps engineers and site reliability engineers working with Kubernetes.

1

Create the Deployment header and metadata

Create a YAML file starting with apiVersion: apps/v1, kind: Deployment, and metadata with name: webapp-deployment.

Kubernetes

# Your code here

Hint

Start by specifying the API version, the kind of resource, and the deployment name under metadata.

2

Add replicas and selector to the spec

Add a spec section with replicas: 3 and a selector matching app: webapp under matchLabels.

Kubernetes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp-deployment
# Add spec with replicas and selector below
# Your code here

Hint

The spec defines how many pods to run and how to select them using labels.

3

Define the pod template with container details

Under spec.template, add metadata.labels with app: webapp. Then add spec.containers with one container named nginx-container using the image nginx:1.21.

Kubernetes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: webapp
# Add template with metadata.labels and containers below
# Your code here

Hint

The pod template defines the pods that will be created. Labels must match the selector. Containers need a name and image.

4

Output the complete Deployment YAML

Print the entire YAML content stored in a variable called deployment_yaml.

Kubernetes

deployment_yaml = '''
apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: webapp
  template:
    metadata:
      labels:
        app: webapp
    spec:
      containers:
      - name: nginx-container
        image: nginx:1.21
'''
# Print the deployment_yaml variable below
# Your code here

Hint

Use print(deployment_yaml) to show the full YAML content.

Practice

1. What is the main purpose of a Deployment in Kubernetes when defined using a YAML file?

easy

A. To manage and update multiple copies of an application smoothly

B. To store data persistently across pods

C. To expose an application to the internet

D. To define network policies between pods

Solution

1. Step 1: Understand Deployment role

   A Deployment manages the lifecycle of pods, ensuring the desired number of replicas run and updates happen smoothly.

2. Step 2: Compare options

   Options B, C, and D describe other Kubernetes resources (PersistentVolume, Service, NetworkPolicy), not Deployment.

3. Final Answer:

   To manage and update multiple copies of an application smoothly -> Option A

4. Quick Check:

   Deployment = Manage app replicas and updates [OK]

Hint: Deployments control app copies and updates, not storage or networking [OK]

Common Mistakes:

• Confusing Deployment with Service or PersistentVolume
• Thinking Deployment exposes apps externally
• Assuming Deployment manages network policies

2. Which of the following YAML snippets correctly sets the number of pod replicas to 3 in a Deployment?

easy

A. replicas: 3

B. replicaCount: 3

C. count: 3

D. podReplicas: 3

Solution

1. Step 1: Identify correct replicas field

   The correct field to specify pod count in Deployment YAML is replicas.

2. Step 2: Check other options

   Fields like replicaCount, count, or podReplicas are invalid and will cause errors.

3. Final Answer:

   replicas: 3 -> Option A

4. Quick Check:

   Use 'replicas' to set pod count [OK]

Hint: Use 'replicas' exactly to set pod count in Deployment YAML [OK]

Common Mistakes:

• Using incorrect field names like replicaCount
• Misspelling 'replicas' or using camelCase
• Placing replicas under wrong YAML level

3. Given this Deployment YAML snippet, what will be the label selector used to match pods?

selector:
  matchLabels:
    app: myapp
    tier: frontend

medium

A. Pods with any label app or tier

B. Pods with label app=myapp only

C. Pods with label tier=frontend only

D. Pods with labels app=myapp and tier=frontend

Solution

1. Step 1: Understand matchLabels selector

   The matchLabels requires all listed labels to match exactly for pod selection.

2. Step 2: Analyze given labels

   Both app: myapp and tier: frontend must be present on pods to match.

3. Final Answer:

   Pods with labels app=myapp and tier=frontend -> Option D

4. Quick Check:

   matchLabels means all labels must match [OK]

Hint: matchLabels requires all labels to match exactly [OK]

Common Mistakes:

• Assuming matchLabels matches any one label
• Confusing matchLabels with matchExpressions
• Ignoring one of the labels in selector

4. You wrote this Deployment YAML but your pods are not created. What is the error?

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp
spec:
  replicas: 2
  selector:
    matchLabels:
      app: webapp
  template:
    metadata:
      labels:
        app: frontend
    spec:
      containers:
      - name: webapp
        image: nginx

medium

A. No container ports defined

B. Incorrect apiVersion for Deployment

C. Selector labels do not match template labels

D. Missing container image tag

Solution

1. Step 1: Check selector and template labels

   The selector matchLabels: app: webapp does not match template labels: app: frontend. Labels must match exactly or Deployment creation fails.

2. Step 2: Verify other fields

   Ports are optional for pod creation; apiVersion is correct; image tag defaults to latest.

3. Final Answer:

   Selector labels do not match template labels -> Option C

4. Quick Check:

   Selector must match template labels [OK]

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

Common Mistakes:

• Assuming container ports are required for pod creation
• Thinking image tag is mandatory
• Confusing apiVersion for Deployment

5. You want to update your Deployment to run 5 replicas and change the container image to 'nginx:1.21'. Which YAML snippet correctly applies both changes?

hard

A. spec:
replicas: 5
template:
spec:
containers:
- name: nginx
image: nginx:1.21

B. spec:
replicas: 5
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:1.21

C. spec:
replicas: 5
containers:
- name: nginx
image: nginx:1.21

D. spec:
template:
spec:
containers:
- name: nginx
image: nginx:1.21
replicas: 5

Solution

1. Step 1: Understand Deployment spec structure

   The replicas field is directly under spec. The pod template is under spec.template, which must include metadata.labels and spec.containers.

2. Step 2: Check each option's correctness

   spec:
     replicas: 5
     template:
       spec:
         containers:
         - name: nginx
           image: nginx:1.21

   misses metadata.labels under template, which is required for selector matching.

   spec:
     replicas: 5
     containers:
     - name: nginx
       image: nginx:1.21

   places containers directly under spec, which is invalid.

   spec:
     template:
       spec:
         containers:
         - name: nginx
           image: nginx:1.21
     replicas: 5

   places replicas after template, which is allowed but missing labels in template metadata.

   spec:
     replicas: 5
     template:
       metadata:
         labels:
           app: nginx
       spec:
         containers:
         - name: nginx
           image: nginx:1.21

   correctly includes replicas, template metadata labels, and container spec with updated image.

3. Final Answer:

   spec: replicas: 5, template with metadata.labels app: nginx, containers image: nginx:1.21 -> Option B

4. Quick Check:

   replicas under spec, labels in template metadata, containers in template spec [OK]

Hint: Always include labels in template metadata for selector matching [OK]

Common Mistakes:

• Omitting labels in pod template metadata
• Placing containers outside template spec
• Misplacing replicas field