[kubernates] 004. Sketching Kubernetes Objects

labels

• Every object has labels.
• Used by other objects to identify and select targets.
• Provides reference points for both administrators and users.

Selector

• Links two objects by matching their labels.
• Not all objects connect this way; some can be linked directly to a Pod.

NameSpace

The role of grouping objects together.

apiVersion: v1
kind: Namespace
metadata:
  name: anotherclass-123
  labels:
    part-of: k8s-anotherclass
    managed-by: dashboard

Deployment

Responsible for creating and upgrading Pods

apiVersion: apps/v1
kind: Deployment
metadata:
  namespace: anotherclass-123
  name: api-tester-1231
  labels:
    part-of: k8s-anotherclass
    component: backend-server
    name: api-tester
    instance: api-tester-1231
    version: 1.0.0
    managed-by: dashboard
spec:
  selector:
    matchLabels:
      part-of: k8s-anotherclass
      component: backend-server
      name: api-tester
      instance: api-tester-1231
  replicas: 2                
  strategy:                  //update strategy
    type: RollingUpdate
  template:                   //contents of the pod
    metadata:
      labels:
        part-of: k8s-anotherclass
        component: backend-server
        name: api-tester
        instance: api-tester-1231
        version: 1.0.0
    spec:
      nodeSelector:           //Selecting a node to run the Pod
        kubernetes.io/hostname: k8s-master
      containers:
        - name: api-tester-1231
          image: zaimyon/api-tester:v1.0.0    //Images pushed to Docker Hub
          ports:
          - name: http
            containerPort: 8080
          envFrom:
            - configMapRef:
                name: api-tester-1231-properties    //Application environment variables
          startupProbe:      //Checking the app's health status
            httpGet:
              path: "/startup"
              port: 8080
            periodSeconds: 5
            failureThreshold: 36
          readinessProbe:     //The value that decides whether to allow traffic
            httpGet:
              path: "/readiness"
              port: 8080
            periodSeconds: 10
            failureThreshold: 3
          livenessProbe:     //Restart the app if it’s not healthy.
            httpGet:
              path: "/liveness"
              port: 8080
            periodSeconds: 10
            failureThreshold: 3
          resources:         // Resource Allocation
            requests:
              memory: "100Mi"
              cpu: "100m"
            limits:
              memory: "200Mi"
              cpu: "200m"
          volumeMounts:        // Mount to the volume
            - name: files
              mountPath: /usr/src/myapp/files/dev
            - name: secret-datasource
              mountPath: /usr/src/myapp/datasource
      volumes:
        - name: files
          persistentVolumeClaim:
            claimName: api-tester-1231-files
        - name: secret-datasource
          secret:
            secretName: api-tester-1231-postgresql

Service

Routes traffic to the Pods.

apiVersion: v1
kind: Service
metadata:
  namespace: anotherclass-123
  name: api-tester-1231
  labels:
    part-of: k8s-anotherclass
    component: backend-server
    name: api-tester
    instance: api-tester-1231
    version: 1.0.0
    managed-by: dashboard
spec:
  selector:
    part-of: k8s-anotherclass
    component: backend-server
    name: api-tester
    instance: api-tester-1231
  ports:
    - port: 80
      targetPort: http
      nodePort: 31231
  type: NodePort

Configmap

Providing environment variables to the Pod.

apiVersion: v1
kind: ConfigMap
metadata:
  namespace: anotherclass-123
  name: api-tester-1231-properties
  labels:
    part-of: k8s-anotherclass
    component: backend-server
    name: api-tester
    instance: api-tester-1231
    version: 1.0.0
    managed-by: dashboard
data:
  spring_profiles_active: "dev"
  application_role: "ALL"
  postgresql_filepath: "/usr/src/myapp/datasource/postgresql-info.yaml"

Secret

Providing environment variables to the Pod. (base64 encoded)

apiVersion: v1
kind: Secret
metadata:
  namespace: anotherclass-123
  name: api-tester-1231-postgresql
  labels:
    part-of: k8s-anotherclass
    component: backend-server
    name: api-tester
    instance: api-tester-1231
    version: 1.0.0
    managed-by: dashboard
stringData:
  postgresql-info.yaml: |
    driver-class-name: "org.postgresql.Driver"
    url: "jdbc:postgresql://postgresql:5431"
    username: "dev"
    password: "dev123"

PV (PersistentVolume)

How much storage space to use

apiVersion: v1
kind: PersistentVolume
metadata:
  name: api-tester-1231-files
  labels:
    part-of: k8s-anotherclass
    component: backend-server
    name: api-tester
    instance: api-tester-1231-files
    version: 1.0.0
    managed-by: dashboard
spec:
  capacity:
    storage: 2G
  volumeMode: Filesystem
  accessModes:
    - ReadWriteMany
  local:
    path: "/root/k8s-local-volume/1231"          //Use this path as a volume
  nodeAffinity:
    required:
      nodeSelectorTerms:
        - matchExpressions:
            - {key: kubernetes.io/hostname, operator: In, values: [k8s-master]}

PVC (PersistentVolumeClaim)

Connecting the PV with the Pod

apiVersion: v1
kind: PersistentVolumeClaim        //Specify the PV for the Pod
metadata:
  namespace: anotherclass-123
  name: api-tester-1231-files
  labels:
    part-of: k8s-anotherclass
    component: backend-server
    name: api-tester
    instance: api-tester-1231
    version: 1.0.0
    managed-by: kubectl
spec:
  resources:
    requests:
      storage: 2G             //Storage capacity
  accessModes:
    - ReadWriteMany
  selector:
    matchLabels:
      part-of: k8s-anotherclass
      component: backend-server
      name: api-tester
      instance: api-tester-1231-files

HPA

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  namespace: anotherclass-123
  name: api-tester-1231-default
  labels:
    part-of: k8s-anotherclass
    component: backend-server
    name: api-tester
    instance: api-tester-1231
    version: 1.0.0
    managed-by: dashboard
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: api-tester-1231
  minReplicas: 2
  maxReplicas: 4
  metrics:
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 60
  behavior:
    scaleUp:
      stabilizationWindowSeconds: 120

• tags :
• Kubernetes