A Job creates one or more Pods and ensures that a specified number of them successfully terminate. As pods successfully complete, the Job tracks the successful completions. When a specified number of successful completions is reached, the task (ie, Job) is complete. Deleting a Job will clean up the Pods it created.
A simple case is to create one Job object in order to reliably run one Pod to completion. The Job object will start a new Pod if the first Pod fails or is deleted (for example due to a node hardware failure or a node reboot).
You can also use a Job to run multiple Pods in parallel.
Create a namespace for this lab:
kubectl create ns lab-16
---
namespace "lab-16" created
Here is an example Job config. It computes π to 2000 places and prints it out. It takes around 10s to complete.
lab-16-job.yml:
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
Now let’s run kubectl create -f lab-16-job.yml -n lab-16 to deploy the example.
kubectl describe jobs/pi -n lab-16
---
Name: pi
Namespace: default
Selector: controller-uid=f08d7c7d-c8c4-11e9-b7ce-42010a84026a
Labels: controller-uid=f08d7c7d-c8c4-11e9-b7ce-42010a84026a
job-name=pi
Annotations: kubectl.kubernetes.io/last-applied-configuration:
{"apiVersion":"batch/v1","kind":"Job","metadata":{"annotations":{},"name":"pi","namespace":"default"},"spec":{"backoffLimit":4,"template":...
Parallelism: 1
Completions: 1
Start Time: Tue, 27 Aug 2019 14:19:38 +0200
Completed At: Tue, 27 Aug 2019 14:20:17 +0200
Duration: 39s
Pods Statuses: 0 Running / 1 Succeeded / 0 Failed
Pod Template:
Labels: controller-uid=f08d7c7d-c8c4-11e9-b7ce-42010a84026a
job-name=pi
Containers:
pi:
Image: perl
Port: <none>
Host Port: <none>
Command:
perl
-Mbignum=bpi
-wle
print bpi(2000)
Environment: <none>
Mounts: <none>
Volumes: <none>
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal SuccessfulCreate 51s job-controller Created pod: pi-vxccp
To view completed Pods of a Job, use kubectl get pods -n lab-16.
To list all the Pods that belong to a Job in a machine readable form, you can use a command like this:
pods=$(kubectl get pods -n lab-16 --selector=job-name=pi --output=jsonpath='{.items[*].metadata.name}')
echo $pods
kubectl logs $pods -n lab-16
3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113305305488204665213841469519415116094330572703657595919530921861173819326117931051185480744623799627495673518857527248912279381830119491298336733624406566430860213949463952247371907021798609437027705392171762931767523846748184676694051320005681271452635608277857713427577896091736371787214684409012249534301465495853710507922796892589235420199561121290219608640344181598136297747713099605187072113499999983729780499510597317328160963185950244594553469083026425223082533446850352619311881710100031378387528865875332083814206171776691473035982534904287554687311595628638823537875937519577818577805321712268066130019278766111959092164201989380952572010654858632788659361533818279682303019520353018529689957736225994138912497217752834791315155748572424541506959508295331168617278558890750983817546374649393192550604009277016711390098488240128583616035637076601047101819429555961989467678374494482553797747268471040475346462080466842590694912933136770289891521047521620569660240580381501935112533824300355876402474964732639141992726042699227967823547816360093417216412199245863150302861829745557067498385054945885869269956909272107975093029553211653449872027559602364806654991198818347977535663698074265425278625518184175746728909777727938000816470600161452491921732172147723501414419735685481613611573525521334757418494684385233239073941433345477624168625189835694855620992192221842725502542568876717904946016534668049886272327917860857843838279679766814541009538837863609506800642251252051173929848960841284886269456042419652850222106611863067442786220391949450471237137869609563643719172874677646575739624138908658326459958133904780275901
When a Job completes, no more Pods are created, but the Pods are not deleted either. Keeping them around allows you to still view the logs of completed pods to check for errors, warnings, or other diagnostic output. The job object also remains after it is completed so that you can view its status. It is up to the user to delete old jobs after noting their status. Delete the job with kubectl (e.g. kubectl delete jobs/pi or kubectl delete -f ./lab-16-job.yml). When you delete the job using kubectl, all the pods it created are deleted too.
A Cron Job creates Jobs on a time-based schedule.
One CronJob object is like one line of a crontab (cron table) file. It runs a job periodically on a given schedule, written in Cron format.
Cron jobs require a config file. This example cron job config .spec file prints the current time and a hello message every minute:
Check out the following CronJob yaml:
apiVersion: batch/v1beta1
kind: CronJob
metadata:
name: hello
spec:
schedule: "*/1 * * * *"
jobTemplate:
spec:
template:
spec:
containers:
- name: hello
image: busybox
args:
- /bin/sh
- -c
- date; echo Hello from the Kubernetes cluster
restartPolicy: OnFailure
Run the example CronJob by using this command:
kubectl create -f https://k8s.io/examples/application/job/cronjob.yaml -n lab-16
After creating the cron job, get its status using this command:
kubectl get cronjob hello -n lab-16
As you can see from the results of the command, the cron job has not scheduled or run any jobs yet. Watch for the job to be created in around one minute:
kubectl get jobs --watch -n lab-16
The output is similar to this:
NAME COMPLETIONS DURATION AGE
hello-4111706356 0/1 0s
hello-4111706356 0/1 0s 0s
hello-4111706356 1/1 5s 5s
Now, find the pods that the last scheduled job created and view the standard output of one of the pods.
# Replace "hello-4111706356" with the job name in your system
pods=$(kubectl get pods -n lab-16 --selector=job-name=hello-4111706356 --output=jsonpath={.items[].metadata.name})
Show pod log:
kubectl logs $pods -n lab-16
Tue Aug 27 12:58:07 UTC 2019
Hello from the Kubernetes cluster
Delete the Cron Job
kubectl delete cronjob hello -n lab-16
In order to delete our daemonset use the following command:
kubectl delete ns lab-16
---
namespace "lab-16" deleted