Mastering Kubernetes ReplicaSets and Deployments#

1. Create a ReplicaSet#

First, we’ll create a ReplicaSet based on the nginx image with 3 replicas:

1
apiVersion: apps/v1
2
kind: ReplicaSet
3
metadata:
4
  name: nginx-replicaset
5
spec:
6
  replicas: 3
7
  selector:
8
    matchLabels:
9
      app: nginx
10
  template:
11
    metadata:
12
      labels:
13
        app: nginx
14
    spec:
15
      containers:
16
        - name: nginx
17
          image: nginx

Save this as nginx-replicaset.yaml and apply it:

1
kubectl apply -f nginx-replicaset.yaml

2. Update Replicas in YAML#

To update the replicas to 4, modify the replicas field in the YAML file:

1
spec:
2
  replicas: 4

Apply the changes:

1
kubectl apply -f nginx-replicaset.yaml

3. Update Replicas via Command Line#

To scale the ReplicaSet to 6 replicas using the command line:

1
kubectl scale replicaset nginx-replicaset --replicas=6

1. Create a Deployment#

Create a Deployment named nginx with 3 replicas:

1
apiVersion: apps/v1
2
kind: Deployment
3
metadata:
4
  name: nginx
5
  labels:
6
    tier: backend
7
spec:
8
  replicas: 3
9
  selector:
10
    matchLabels:
11
      app: v1
12
  template:
13
    metadata:
14
      labels:
15
        app: v1
16
    spec:
17
      containers:
18
        - name: nginx
19
          image: nginx:1.23.0

Save this as nginx-deployment.yaml and apply it:

1
kubectl apply -f nginx-deployment.yaml

2. List the Deployment#

Verify the Deployment:

1
kubectl get deployments

3. Update the Image#

Update the image to nginx:1.23.4:

1
kubectl set image deployment/nginx nginx=nginx:1.23.4

4. Verify the Rollout#

Check the rollout status:

1
kubectl rollout status deployment/nginx

5. Assign Change Cause#

Record the change cause:

1
kubectl annotate deployment/nginx kubernetes.io/change-cause="Pick up patch version"

6. Scale the Deployment#

Scale to 5 replicas:

1
kubectl scale deployment/nginx --replicas=5

7. View Rollout History#

Check the rollout history:

1
kubectl rollout history deployment/nginx

8. Rollback to Revision 1#

Rollback to the first revision:

1
kubectl rollout undo deployment/nginx --to-revision=1

9. Verify Image Version#

Check the current image version:

1
kubectl describe deployment nginx | grep Image:

Issue 1: Invalid Kind#

Apply the following YAML:

1
apiVersion: v1
2
kind: Deployment
3
metadata:
4
  name: nginx-deploy
5
  labels:
6
    env: demo
7
spec:
8
  template:
9
    metadata:
10
      labels:
11
        env: demo
12
      name: nginx
13
    spec:
14
      containers:
15
        - image: nginx
16
          name: nginx
17
          ports:
18
            - containerPort: 80
19
  replicas: 3
20
  selector:
21
    matchLabels:
22
      env: demo

You’ll encounter an error because the apiVersion and kind don’t match. To fix this:

1. Change apiVersion: v1 to apiVersion: apps/v1
2. Apply the corrected YAML

Issue 2: Mismatched Labels#

Apply the following YAML:

1
apiVersion: v1
2
kind: Deployment
3
metadata:
4
  name: nginx-deploy
5
  labels:
6
    env: demo
7
spec:
8
  template:
9
    metadata:
10
      labels:
11
        env: demo
12
      name: nginx
13
    spec:
14
      containers:
15
        - image: nginx
16
          name: nginx
17
          ports:
18
            - containerPort: 80
19
  replicas: 3
20
  selector:
21
    matchLabels:
22
      env: dev

This will create a Deployment, but it won’t be able to manage any Pods due to mismatched labels. To fix this:

1. Change the selector.matchLabels.env from dev to demo to match the Pod template labels
2. Change apiVersion: v1 to apiVersion: apps/v1
3. Apply the corrected YAML