Declarative YAML

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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
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apiVersion: v1
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kind: Pod
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metadata:
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  name: nginx
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spec:
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  containers:
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  - name: nginx
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    image: nginx:1.17.3
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    ports:
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    - containerPort: 80
Copied!
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apiVersion: apps/v1
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kind: Deployment
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metadata:
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  name: nginx-deployment
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spec:
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  selector:
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    matchLabels:
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      app: nginx
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  replicas: 2
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  template:
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    metadata:
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      labels:
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        app: nginx
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    spec:
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      containers:
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      - name: nginx
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        image: nginx:1.17.3
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        ports:
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        - containerPort: 80
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Declaring multiple types in a single file - separate them with "---"
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apiVersion: v1
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kind: Service
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metadata:
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  name: app-nginx-service
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spec:
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  type: NodePort
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  ports:
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  - port: 80
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  selector:
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    app: app-nginx
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--- # !!! Separator
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apiVersion: apps/v1
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kind: Deployment
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metadata:
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  name: app-nginx-deployment
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spec:
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  replicas: 3
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  selector:
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    matchLabels:
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      app: app-nginx
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  template:
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    metadata:
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      labels:
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        app: app-nginx
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    spec:
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      containers:
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      - name: nginx
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        image: nginx:1.17.3
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        ports:
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        - containerPort: 80
Copied!
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
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Kubernetes Management Techniques
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Dry Runs with Apply YAML