Creating Deployment

• We learned few type of Kubernetes Resource
  • Service
  • Pod
  • ReplicaSet
• While Service is a higher-level concept we be creating in the future, Pods and ReplicaSet are considered lower-level concept.
• Deployment doesn't manage our app, but rather Deployment creates a ReplicaSet which in turns manages Pods.
• Deployment is a way to define the states of our application declaratively.
• With help of Deployment we can easily deploy our application, plus it is super easy to update them.
• Deployment shines when we are about to upgrade the app to new version.
• Out of the box it supports rolling updates, but other strategies are also easily achievable. We will discuss deployment strategies later.

+----------+          +----------+
|Deployment+--------->+ReplicaSet|
+----------+          +------+---+
                             |
                             |
  +------------+-------------+
  |            |             |
+-v-+        +-v-+         +-v-+
|Pod|        |Pod|         |Pod|
+---+        +---+         +---+

Creating Deployment

• Creating Deployment is same as creating ReplicaSet
• If you have ReplicaSet config file from before, you can easily make it Deployment resource.
• Actually we can even delete some properties. We will delete it later, and explain why we can delete them.
• For now let's replace the property kind: Service to kind: Deployment.
• And there you have it. You just created your Deployment resource.

apiVersion: apps/v1
kind: Deployment       # kind: ReplicaSet
metadata:
  name: web
  labels:
    version: v1
    env: prod
spec:
  replicas: 3
  selector:
    matchLabels:
      env: prod
      version: v1
  template:
    metadata:
      name: web
      labels:
        version: v1
        env: prod
    spec:
      containers:
        - image: amantuladhar/docker-kubernetes:v1-web
          name: web
          # Liveness & readiness probe
          ports:
            - containerPort: 8080

• If you create a resource using kubectrl create -f deployment.yaml you will create your resources.
• If you list the resources, you can see Deployment will create ReplicaSet, Pods.
• Number of Pods also match the replicas: @number.

Deployment doesn't create Service

• If you listed the resources kubectl get all you may have noticed, we don't have our Service running.
• To access Pods we need to create a Service.

Rolling out Update

Upgrade the app (V2)

containers:
  - image: amantuladhar/docker-kubernetes:v2-web
    name: web

• Now let's create update start the update process
• You can use kubectl apply -f deployment.yaml
• By default Deployment favors rolling update.

Because Deployment is not tied to specific version of app, we can delete the label version label selector from our yaml file.