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Kubernetes - Liveness & Readiness Probes

Step-01: Introduction

  • Refer Probes slide for additional details

Kubernetes Manifests

#01-storage-class.yml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata: 
  name: ebs-sc
provisioner: ebs.csi.aws.com
volumeBindingMode: WaitForFirstConsumer 

#02-persistent-volume-claim.yml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: ebs-mysql-pv-claim
spec: 
  accessModes:
    - ReadWriteOnce
  storageClassName: ebs-sc
  resources: 
    requests:
      storage: 4Gi

#03-UserManagement-ConfigMap.yml
apiVersion: v1
kind: ConfigMap
metadata:
  name: usermanagement-dbcreation-script
data: 
  mysql_usermgmt.sql: |-
    DROP DATABASE IF EXISTS usermgmt;
    CREATE DATABASE usermgmt; 

#04-mysql-deployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: mysql
spec: 
  replicas: 1
  selector:
    matchLabels:
      app: mysql
  strategy:
    type: Recreate 
  template: 
    metadata: 
      labels: 
        app: mysql
    spec: 
      containers:
        - name: mysql
          image: mysql:5.6
          env:
            - name: MYSQL_ROOT_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: mysql-db-password
                  key: db-password 
          ports:
            - containerPort: 3306
              name: mysql    
          volumeMounts:
            - name: mysql-persistent-storage
              mountPath: /var/lib/mysql    
            - name: usermanagement-dbcreation-script
              mountPath: /docker-entrypoint-initdb.d #https://hub.docker.com/_/mysql Refer Initializing a fresh instance                                            
      volumes: 
        - name: mysql-persistent-storage
          persistentVolumeClaim:
            claimName: ebs-mysql-pv-claim
        - name: usermanagement-dbcreation-script
          configMap:
            name: usermanagement-dbcreation-script

#05-mysql-clusterip-service.yml
apiVersion: v1
kind: Service
metadata: 
  name: mysql
spec:
  selector:
    app: mysql 
  ports: 
    - port: 3306  
  clusterIP: None # This means we are going to use Pod IP    

#06-UserManagementMicroservice-Deployment-Service.yml
apiVersion: apps/v1
kind: Deployment 
metadata:
  name: usermgmt-microservice
  labels:
    app: usermgmt-restapp
spec:
  replicas: 1
  selector:
    matchLabels:
      app: usermgmt-restapp
  template:  
    metadata:
      labels: 
        app: usermgmt-restapp
    spec:
      initContainers:
        - name: init-db
          image: busybox:1.31
          command: ['sh', '-c', 'echo -e "Checking for the availability of MySQL Server deployment"; while ! nc -z mysql 3306; do sleep 1; printf "-"; done; echo -e "  >> MySQL DB Server has started";']      
      containers:
        - name: usermgmt-restapp
          image: stacksimplify/kube-usermanagement-microservice:1.0.0
          ports: 
            - containerPort: 8095           
          env:
            - name: DB_HOSTNAME
              value: "mysql"            
            - name: DB_PORT
              value: "3306"            
            - name: DB_NAME
              value: "usermgmt"            
            - name: DB_USERNAME
              value: "root"            
            - name: DB_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: mysql-db-password
                  key: db-password           
          livenessProbe:
            exec:
              command: 
                - /bin/sh
                - -c 
                - nc -z localhost 8095
            initialDelaySeconds: 60
            periodSeconds: 10
          readinessProbe:
            httpGet:
              path: /usermgmt/health-status
              port: 8095
            initialDelaySeconds: 60
            periodSeconds: 10                                   

#07-UserManagement-Service.yml
apiVersion: v1
kind: Service
metadata:
  name: usermgmt-restapp-service
  labels: 
    app: usermgmt-restapp
spec:
  type: NodePort
  selector:
    app: usermgmt-restapp
  ports: 
    - port: 8095
      targetPort: 8095
      nodePort: 31231

#08-kubernetes-secrets.yml
apiVersion: v1
kind: Secret
metadata:
  name: mysql-db-password
type: Opaque
data: 
  db-password: ZGJwYXNzd29yZDEx

Step-02: Create Liveness Probe with Command

          livenessProbe:
            exec:
              command:
                - /bin/sh
                - -c
                - nc -z localhost 8095
            initialDelaySeconds: 60
            periodSeconds: 10

Step-03: Create Readiness Probe with HTTP GET

          readinessProbe:
            httpGet:
              path: /usermgmt/health-status
              port: 8095
            initialDelaySeconds: 60
            periodSeconds: 10

Step-04: Create k8s objects & Test

# Create All Objects
kubectl apply -f kube-manifests/

# List Pods
kubectl get pods

# Watch List Pods screen
kubectl get pods -w

# Describe Pod & Discuss about init container
kubectl describe pod <usermgmt-microservice-xxxxxx>

# Access Application Health Status Page
http://<WorkerNode-Public-IP>:31231/usermgmt/health-status
- Observation: User Management Microservice pod witll not be in READY state to accept traffic until it completes the initialDelaySeconds=60seconds.

AWS EKS - Elastic Kubernetes Service - Masterclass

Image

Step-05: Clean-Up

  • Delete all k8s objects created as part of this section 
    # Delete All
kubectl delete -f kube-manifests/

# List Pods
kubectl get pods

# Verify sc, pvc, pv
kubectl get sc,pvc,pv

References:

  • https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/