Kubernetes Deployment: The ultimate guide

1. Deployment Creation

Imperative Command

kubectl create deployment <deployment-name> --image=<image-name> --replicas=<number-of-replicas>

Example:

kubectl create deployment my-app --image=nginx:1.21 --replicas=3

Declarative Approach (YAML File)

Create a file deployment.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: nginx
        image: nginx:1.21
        ports:
        - containerPort: 80

Apply the YAML file:

kubectl apply -f deployment.yaml

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2. Update Deployment

Rolling Update

Modify the YAML file to update the image:

      containers:
      - name: nginx
        image: nginx:1.22

Apply the changes:

kubectl apply -f deployment.yaml

OR, using imperative command:

kubectl set image deployment/<deployment-name> <container-name>=<new-image>

Example:

kubectl set image deployment/my-app nginx=nginx:1.22

Rolling Update Status

Check the status of a rolling update:

kubectl rollout status deployment/<deployment-name>

Example:

kubectl rollout status deployment/my-app

Rollback Deployment

Rollback to the previous version:

kubectl rollout undo deployment/<deployment-name>

Example:

kubectl rollout undo deployment/my-app

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3. Update Strategies

Recreate Strategy

All existing pods are terminated before new ones are created.

spec:
  strategy:
    type: Recreate

RollingUpdate Strategy

Default strategy where pods are updated incrementally.

spec:
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1   # Extra pods allowed during update
      maxUnavailable: 1 # Pods allowed to be unavailable during update

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4. Useful Deployment Commands

1. Describe a Deployment
   Provides detailed information:

    kubectl describe deployment <deployment-name>
   

   Example:

    kubectl describe deployment my-app
   

2. List All Deployments

    kubectl get deployments
   

3. Get Pods Managed by a Deployment

    kubectl get pods -l app=<app-label>
   

   Example:

    kubectl get pods -l app=my-app
   

4. Scale a Deployment
   Increase or decrease replicas:

    kubectl scale deployment <deployment-name> --replicas=<number>
   

   Example:

    kubectl scale deployment my-app --replicas=5
   

5. View Deployment History

    kubectl rollout history deployment/<deployment-name>
   

   Example:

    kubectl rollout history deployment/my-app
   

6. Delete a Deployment

    kubectl delete deployment <deployment-name>
   

   Example:

    kubectl delete deployment my-app
   

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5. YAML for Various Strategies

Recreate Deployment Example

apiVersion: apps/v1
kind: Deployment
metadata:
  name: recreate-deployment
spec:
  replicas: 2
  strategy:
    type: Recreate
  selector:
    matchLabels:
      app: recreate-app
  template:
    metadata:
      labels:
        app: recreate-app
    spec:
      containers:
      - name: nginx
        image: nginx:1.21

Rolling Update Deployment Example

apiVersion: apps/v1
kind: Deployment
metadata:
  name: rolling-update-deployment
spec:
  replicas: 3
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 2
      maxUnavailable: 1
  selector:
    matchLabels:
      app: rolling-app
  template:
    metadata:
      labels:
        app: rolling-app
    spec:
      containers:
      - name: nginx
        image: nginx:1.21

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Summary of Key Commands

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These commands and YAML files will help you manage deployments effectively in Kubernetes.