1. pod life cycle

init container

Case: when the service monitored by the init container is not configured, the main container and init container cannot start normally

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
spec:
  containers:
  - name: myapp-container
    image: busyboxplus
    command: ['sh', '-c', 'echo The app is running! && sleep 3600']
  initContainers:
  - name: init-myservice
    image: busyboxplus
    command: ['sh', '-c', "until nslookup myservice.default.svc.cluster.local; do echo waiting for myservice; sleep 2; done"]
  - name: init-mydb
    image: busyboxplus
    command: ['sh', '-c', "until nslookup mydb.default.svc.cluster.local; do echo waiting for mydb; sleep 2; done"]

#---
#apiVersion: v1
#kind: Service
#metadata:
#  name: myservice
#spec:
#  ports:
#  - protocol: TCP
#    port: 80
#    targetPort: 9376
#---
#apiVersion: v1
#kind: Service
#metadata:
#  name: mydb
#spec:
#  ports:
#  - protocol: TCP
#    port: 80
#    targetPort: 9377

Delete the pod, cancel the comment, and reopen the container to run normally

probe

Case: the probe detects the container port and publishes files. When the conditions are not met, the container cannot be started.

apiVersion: v1
kind: Pod
metadata:
  name: pod-ex2
  labels:
    app: myapp
spec:
  containers:
  - name: myapp
    image: myapp:v1
    imagePullPolicy: IfNotPresent
    livenessProbe:
      tcpSocket: #Monitor port 80
        port: 80 
      initialDelaySeconds: 1
      periodSeconds: 3
      timeoutSeconds: 1
    readinessProbe:
      httpGet: #Monitor release files
        path: /test.html 
        port: 80
      initialDelaySeconds: 1
      periodSeconds: 3
      timeoutSeconds: 1

Test does not exist HTML, build the pod, and cannot run the pod successfully

Add required files

kubectl exec pod-ex2  sh -i -t
/ # echo westos> /usr/share/nginx/html/test.html

The pod successfully enters the ready state

2. Controller

Replication Controller and ReplicaSet

ReplicaSet replicaset is officially recommended to support the new set based selector requirements. ReplicaSet ensures that a specified number of Pod replicas are running at any time.
Although ReplicaSets can be used independently, today it is mainly used by Deployments as a mechanism to coordinate Pod creation, deletion and update.

Write a configuration file to verify the copy and establish the capacity expansion function. The version cannot be upgraded or rolled back using this controller

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: replicaset-example
spec:
  replicas: 6#12
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: myapp
        image: myapp:v1

When the number of copies is 6:
When modified to 12:

Deployment

It is used to create Pod and ReplicaSet, scroll update and rollback, expand and shrink capacity
, pause and resume.
vim deployment.yml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deployment
  labels:
    app: myapp
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: myapp
        image: myapp:v1 #Specify the mirror as v1

Run the deployment to view the container status
Change the image to v2 and rebuild the pod

        image: myapp:v2 #Specify the mirror as v2

deployment will re-establish an rs controller to create a replica of v2. The rs of v1 will not be discarded and used for

DaemonSet

The daemon set ensures that a copy of the Pod is running on all (or some) nodes. When nodes join the cluster, a Pod will also be added for them. When a node is removed from the cluster, these pods will also be recycled. Deleting a DaemonSet will delete all pods it creates. Generally, run the cluster storage DaemonSet, log collection DaemonSet, and monitoring DaemonSet on each node.

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: daemonset-example
  labels:
    k8s-app: zabbix-agent
spec:
  selector:
    matchLabels:
      name: zabbix-agent
  template:
    metadata:
      labels:
        name: zabbix-agent
    spec:
      containers:
      - name: zabbix-agent
        image: zabbix/zabbix-agent

StatefulSet

StatefulSet is an API object used to manage workload of stateful applications. For applications where there are unequal relationships between instances and instances have dependencies on external data, StatefulSet is used to manage Deployment and extend a group of pods, and can provide sequence number and uniqueness guarantee for these pods

Job and CronJob

Job is used to execute batch tasks. It only executes the task once to ensure that one or more pods of the task end successfully.

Cron Job creates Jobs based on time scheduling. A CronJob object is like a line in a crontab (cron table) file. It is written in Cron format and executes Jobs periodically at a given scheduling time.

#job
$ vim job-example.yaml
apiVersion: batch/v1
kind: Job
metadata:
  name: pi
spec:
  template:
    spec:
      containers:
      - name: pi
        image: perl
        command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(2000)"]
      restartPolicy: Never
  backoffLimit: 4
$ kubectl apply -f job-example.yaml
$ kubectl get pod
NAME       READY   STATUS      RESTARTS   AGE
pi-6phk8   0/1     Completed   0          2m22s
$ kubectl logs pi-6phk8
$ kubectl delete job pi

#cornjob

apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: cronjob-example
spec:
  schedule: "* * * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: cronjob
            image: busybox
            args:
            - /bin/sh
            - -c
            - date; echo Hello from k8s cluster
          restartPolicy: OnFailure

HPA

Automatically adjust the number of pods in the service according to the resource utilization to realize the automatic scaling of Pod level.