Day39 - Kubernetes - jobs, cronjobs, etcd

 Kubernetes 04/14/2021
Todays topic:- jobs, cronjob, etcd

Jobs
----
Launch your minikube
> minukube start

Container is equal to process

image -> launch -> container -> process
life of a container is a life of process
process killed, container is killed.

When you launch a container, the life of conainer is infinite.
unless you delete it. Any pod we launch is a server - webserver.
- These server never stop.
- They keep on running
- If they fail, by default we have policy - always policy
   There are multiple policies and always is one of them.

restart policy on POD.

batch processing


> kc get job

deployment also launch pod and if they stop, they start automatically.
if job completed, they don't relaunch.

we want some job run on some interval.

We can get it schdule it using crontjob
> kc get cronjob

if you have a work, to run particular job say batch job, kubernetes has a resource: job, crontab



# echo $SHELL
bash

lets take a look on a simple eg,
$ for i in 1 2 3 4 5 6 ; do echo $i; done


Lets create a deployment
> kc create deploy myd --image=centos:7 -o yaml >j.yaml


[root@master ~]# kc create deploy myd --image=centos:7 -o yaml >j.yaml
[root@master ~]# cat j.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: myd
  name: myd
  namespace: default
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myd
  template:
    metadata:
      labels:
        app: myd
    spec:
      containers:
      - image: centos:7
        imagePullPolicy: IfNotPresent
        name: centos
         #- "/bin/bash"
         - "/bin/sh"
         - "-c"
         - "for i in 1 2 3 4 5 6; do echo $i; done"
      restartPolicy: Always #(or Never)
 
[root@master ~]#

> kc apply j.yaml
> kc get pods



[root@master ~]# cat j.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: myd
  name: myd
  namespace: default
spec:
  completitions: 6
  replicas: 3
  selector:
    matchLabels:
      app: myd
  template:
    metadata:
      labels:
        app: myd
    spec:
      containers:
      - image: centos:7
        imagePullPolicy: IfNotPresent
        name: centos
         #- "/bin/bash"
         - "/bin/sh"
         - "-c"
         - "for i in 1 2 3 4 5 6; do echo $i; done"
      restartPolicy: Always #(or Never)
 
[root@master ~]#


[root@master ~]# cat j.yaml
apiVersion: apps/v1
kind: Job
metadata:
  labels:
    app: myd
  name: myd
  namespace: default
spec:
  completitions: 6
  parallellism: 2
  replicas: 3
  selector:
    matchLabels:
      app: myd
  template:
    metadata:
      labels:
        app: myd
    spec:
      containers:
      - image: centos:7
        name: centos
        command: [ "expr", "2", "+", "4" ]
      restartPolicy: Always #(or Never)
 
[root@master ~]#
> kc apply j.yaml

> kc get po
> kc delete job --all

cronjob

[root@master ~]# cat j.yaml
apiVersion: apps/v1
kind: Cronjob
metadata:
  labels:
    app: myd
  name: myd
  namespace: default
spec:
  schedule: "*/2 * * * *"    # every 2 min
  jobTemplate:
   spec:
    completitions: 6    # 6 total
    parallellism: 2    # 2 in parallel
    replicas: 3
    selector:
      matchLabels:
        app: myd
    template:
      metadata:
        labels:
          app: myd
      spec:
        containers:
        - image: centos:7
          name: centos
          command: [ "expr", "2", "+", "4" ]
        restartPolicy: Always #(or Never)
 
[root@master ~]#


>kc deletete job --all
> kc apply -f j.yaml
> ck get pods