How to Create Kubernetes Deployment Using YAML

To create a Kubernetes deployment using yaml, define a Deployment resource with apiVersion, kind, metadata, and spec sections. Then apply it with kubectl apply -f filename.yaml to deploy your application.

Syntax

A Kubernetes deployment YAML file has these main parts:

• apiVersion: Specifies the Kubernetes API version, usually apps/v1.
• kind: The resource type, here it is Deployment.
• metadata: Contains the deployment name and labels.
• spec: Defines the desired state, including replicas, selector, and template for pods.

yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: my-container
        image: my-image:latest
        ports:
        - containerPort: 80

Example

This example creates a deployment named nginx-deployment with 2 replicas running the nginx:1.21.6 image. It shows how to define labels, replicas, and container details.

yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.21.6
        ports:
        - containerPort: 80

Output

deployment.apps/nginx-deployment created

Common Pitfalls

Common mistakes when creating deployments with YAML include:

• Missing or incorrect selector.matchLabels that must match template.metadata.labels.
• Forgetting to specify replicas, which defaults to 1 but might not be intended.
• Using an invalid or missing container image.
• Indentation errors in YAML causing parsing failures.

yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: bad-deployment
spec:
  replicas: 2
  selector:
    matchLabels:
      app: wrong-label  # Does not match template labels
  template:
    metadata:
      labels:
        app: right-label
    spec:
      containers:
      - name: app
        image: nginx:latest
        ports:
        - containerPort: 80

# Corrected selector to match template labels
apiVersion: apps/v1
kind: Deployment
metadata:
  name: good-deployment
spec:
  replicas: 2
  selector:
    matchLabels:
      app: right-label
  template:
    metadata:
      labels:
        app: right-label
    spec:
      containers:
      - name: app
        image: nginx:latest
        ports:
        - containerPort: 80

Quick Reference

Remember these tips when writing deployment YAML:

• apiVersion: Use apps/v1 for deployments.
• selector.matchLabels: Must exactly match template.metadata.labels.
• replicas: Number of pod copies to run.
• containers: Define container name, image, and ports.
• Apply with kubectl apply -f yourfile.yaml.

Key Takeaways

Define a deployment YAML with apiVersion, kind, metadata, and spec sections.

Ensure selector.matchLabels matches template.metadata.labels exactly.

Specify the number of replicas to control pod count.

Use kubectl apply -f filename.yaml to create or update the deployment.

Check YAML indentation carefully to avoid errors.