Deployment

---

• Deployment is like a manager in kubernetes.
• Deployment manages ReplicaSets, supports rollbacks, and updates the currently running application version.
• Definition for creating Deployment is same as ReplicaSets. Value of kind field is replaced with Deployment

---

apiVersion: apps/v1
kind: Deployment
metadata:
  name: server
  labels:
    app: webserver
    env: prod
spec:
  replicas: 3
  selector:
    matchLabels:
      env: prod
  template:
    metadata:
      labels:
        env: prod
    spec:
      containers:
      - name: nginx
        image: nginx
 

---

• The .spec.replicas is a field that specifies the desired number of pod you want to run at any given time.
• The .spec.selector is a label selector which tells the ReplicaSet how to find which Pods it should manage.
• The .spec.template is a pod template that ReplicaSet will manage.
• The .spec.template.metadata.labels are the labels given to the pod which will be manage/created by ReplicaSet. This is crucial as ReplicaSet will manages all the pods with labels that match the selector and hence .spec.template.metadata.labels must be equal to the .spec.selector.

---

Rollout and Versioning

• when we create Deployment it creates a rollout of new version of applications and new revision of Deployment is created.
• If the current revision has some errors we can revert back to older Deployment

Deloyment Strategy

• Recreate and RollingUpdate strategy are used to deploy new version of application
• Recreate will bring all pods down and starts new ones with new version
• RollingUpdate will bring one pod down and start new one and so on
• RollingUpdate is default strategy
• See Blue Green and Canary Deployment to see Additional Strategy

---

Commands

1. create deployment

kubectl create -f deployment-definition.yml

2. get deplotment

kubectl get deployments

3. describe deployment

kubectl describe deployment <deployment-name>

4. rollout status

kubectl rollout status <deployment-name>

5. rollout history

kubectl rollout history <deployment-name>

6. rollout undo

kubectl rollout undo <deployment-name>

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⬅️ ReplicaSets | Service ➡️

References