Completek8s Classroomnotes 03/Aug/2023

Kubernetes Contd

Experiments:

• Try creating a pod with
  • alpine container with sleep 10s
  • observe the failures after 10 s

---
apiVersion: v1
kind: Pod
metadata:
  name: exp1
spec:
  containers:
    - name: exp1
      image: alpine
      command:
        - sleep
        - 10s

* Observations: IN this case kubernetes is try to restart the container once the docker container has finished execution

• Try creating a pod with 2 containers
  • one container put sleep 1d
  • other container put sleep 5s
  • observe failures

---
apiVersion: v1
kind: Pod
metadata:
  name: exp2
spec:
  containers:
    - name: first
      image: alpine
      command:
        - sleep
        - 1d
    - name: second
      image: alpine
      command:
        - sleep
        - 5s

* Now execute kubectl get pod exp2 -o yaml

apiVersion: v1
kind: Pod
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"v1","kind":"Pod","metadata":{"annotations":{},"name":"exp2","namespace":"default"},"spec":{"containers":[{"command":["sleep","1d"],"image":"alpine","name"
:"first"},{"command":["sleep","5s"],"image":"alpine","name":"second"}]}}
  creationTimestamp: "2023-08-03T13:10:53Z"
  name: exp2
  namespace: default
  resourceVersion: "1566"
  uid: 530f8716-7573-4c5d-9183-d7b1c4364159
spec:
  containers:
  - command:
    - sleep
    - 1d
    image: alpine
    imagePullPolicy: Always
    name: first
    resources: {}
    terminationMessagePath: /dev/termination-log
    terminationMessagePolicy: File
    volumeMounts:
    - mountPath: /var/run/secrets/kubernetes.io/serviceaccount
      name: kube-api-access-pbncq
      readOnly: true
  - command:
    - sleep
    - 5s
    image: alpine
    imagePullPolicy: Always
    name: second
    resources: {}
    terminationMessagePath: /dev/termination-log
    terminationMessagePolicy: File
    volumeMounts:
    - mountPath: /var/run/secrets/kubernetes.io/serviceaccount
      name: kube-api-access-pbncq
      readOnly: true
  dnsPolicy: ClusterFirst
  enableServiceLinks: true
  nodeName: node2
  preemptionPolicy: PreemptLowerPriority
  priority: 0
  restartPolicy: Always
  schedulerName: default-scheduler
  securityContext: {}
  serviceAccount: default
  serviceAccountName: default
  terminationGracePeriodSeconds: 30
  tolerations:
  - effect: NoExecute
    key: node.kubernetes.io/not-ready
    operator: Exists
    tolerationSeconds: 300
  - effect: NoExecute
    key: node.kubernetes.io/unreachable
    operator: Exists
    tolerationSeconds: 300
  volumes:
  - name: kube-api-access-pbncq
    projected:
      defaultMode: 420
      sources:
      - serviceAccountToken:
          expirationSeconds: 3607
          path: token
      - configMap:
          items:
          - key: ca.crt
            path: ca.crt
          name: kube-root-ca.crt
      - downwardAPI:
          items:
          - fieldRef:
              apiVersion: v1
              fieldPath: metadata.namespace
            path: namespace
status:
  conditions:
  - lastProbeTime: null
    lastTransitionTime: "2023-08-03T13:10:53Z"
    status: "True"
    type: Initialized
  - lastProbeTime: null
    lastTransitionTime: "2023-08-03T13:14:24Z"
    message: 'containers with unready status: [second]'
    reason: ContainersNotReady
    status: "False"
    type: Ready
  - lastProbeTime: null
    lastTransitionTime: "2023-08-03T13:14:24Z"
    message: 'containers with unready status: [second]'
    reason: ContainersNotReady
    status: "False"
    type: ContainersReady
  - lastProbeTime: null
    lastTransitionTime: "2023-08-03T13:10:53Z"
    status: "True"
    type: PodScheduled
  containerStatuses:
  - containerID: containerd://aad78c31e83c5951b8a316a2a31ba8656e5a729512a9a47bd24a5f1db5e57144
    image: docker.io/library/alpine:latest
    imageID: docker.io/library/alpine@sha256:82d1e9d7ed48a7523bdebc18cf6290bdb97b82302a8a9c27d4fe885949ea94d1
    lastState: {}
    name: first
    ready: true
    restartCount: 0
    started: true
    state:
      running:
        startedAt: "2023-08-03T13:10:54Z"
  - containerID: containerd://287e000ae3a66b9227fc4ec55c345f939f905bb7e2750c36bf0732d8ace7accb
    image: docker.io/library/alpine:latest
    imageID: docker.io/library/alpine@sha256:82d1e9d7ed48a7523bdebc18cf6290bdb97b82302a8a9c27d4fe885949ea94d1
    lastState:
      terminated:
        containerID: containerd://287e000ae3a66b9227fc4ec55c345f939f905bb7e2750c36bf0732d8ace7accb
        exitCode: 0
        finishedAt: "2023-08-03T13:14:24Z"
        reason: Completed
        startedAt: "2023-08-03T13:14:19Z"
    name: second
    ready: false
    restartCount: 5
    started: false
    state:
      waiting:
        message: back-off 2m40s restarting failed container=second pod=exp2_default(530f8716-7573-4c5d-9183-d7b1c4364159)
        reason: CrashLoopBackOff
  hostIP: 192.168.0.22
  phase: Running
  podIP: 10.5.1.3
  podIPs:
  - ip: 10.5.1.3
  qosClass: BestEffort
  startTime: "2023-08-03T13:10:53Z"

• Container states in a pod Refer Here
• Pod lifecycle Phases Refer Here
• Restart policy Refer Here
• Create a Pod spec which will restart Containers
  • only when failed
  • Always
  • Figure out if we can stop restarting containers after 4 attempts
• Restart policy Never and impact on status

---
apiVersion: v1
kind: Pod
metadata:
  name: exp3
spec:
  restartPolicy: Never
  containers:
    - name: exp1
      image: alpine
      command:
        - sleep
        - 10s

• In this case the pod has gone into completed state

---
apiVersion: v1
kind: Pod
metadata:
  name: exp4
spec:
  restartPolicy: Never
  containers:
    - name: exp1
      image: alpine
      command:
        - sleep
        - 10s
        - &&
        - exit 1

• Create a Pod spec which will restart Containers
  • only when failed
  • Figure out if we can stop restarting containers after 4 attempts
• Try to run a jenkins container in docker and see the logs docker logs

apiVersion: v1
kind: Pod
metadata:
  name: jenkins
spec:
  restartPolicy: OnFailure
  containers:
    - name: jenkins
      image: jenkins/jenkins

• Kubectl portforward
  
• Exercise:
  • Try setting up any one of them
    • minikube Refer Here
    • kind Refer Here
• Terms:
  • CPU units
  • memory units