Declarative YAML

• Kubernetes configuration files - YAML or JSON

• Each file contains one or more manifests

• Each manifest describes an API object (deployment, job, secret)

• Each manifest needs 4 parts (root key:values in the file):

  • apiVersion - Which version of the Kubernetes API you’re using to create this object

  • kind - What kind of object you want to create

  • metadata - Data that helps uniquely identify the object, including a name string, UID, and optional namespace

  • spec - What state you desire for the object

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.17.3
    ports:
    - containerPort: 80

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.17.3
        ports:
        - containerPort: 80

Declaring multiple types in a single file - separate them with "---"

apiVersion: v1
kind: Service
metadata:
  name: app-nginx-service
spec:
  type: NodePort
  ports:
  - port: 80
  selector:
    app: app-nginx
--- # !!! Separator
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-nginx-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: app-nginx
  template:
    metadata:
      labels:
        app: app-nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.17.3
        ports:
        - containerPort: 80

• kubectl api-resources

• kubectl api-versions

• We can get all the keys each kind supports: kubectl explain <kind> --recursive

• We can drill down into subnodes of the kind:

  kubectl explain <kind>.<subnode>

  kubectl explain services.spec

Dry Runs with Apply YAML

• dry run client-side only:

  kubectl apply -f file.yml --dry-run

• dry run server-side (will compare current file with what's already deployed on server):

  kubectl apply -f file.yml --server-dry-run

• see the diff visually:

  kubectl diff -f file.yml