Kubernetes Jobs and CronJobs
Kubernetes Jobs and CronJobs
Jobs
A Job creates one or more Pods and will continue to retry execution of the Pods until a specified number of them successfully terminate. 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).
lab@k8s1:~$ kubectl get job
No resources found in default namespace.
lab@k8s1:~$ kubectl get job -A
No resources found
lab@k8s1:~$
lab@k8s1:~$ kubectl create job -h
Create a job with the specified name.
Examples:
# Create a job
kubectl create job my-job --image=busybox
# Create a job with a command
kubectl create job my-job --image=busybox -- date
# Create a job from a cron job named "a-cronjob"
kubectl create job test-job --from=cronjob/a-cronjob
Options:
--allow-missing-template-keys=true: If true, ignore any errors in templates when a field or map key is missing in
the template. Only applies to golang and jsonpath output formats.
--dry-run='none': Must be "none", "server", or "client". If client strategy, only print the object that would be
sent, without sending it. If server strategy, submit server-side request without persisting the resource.
--field-manager='kubectl-create': Name of the manager used to track field ownership.
--from='': The name of the resource to create a Job from (only cronjob is supported).
--image='': Image name to run.
-o, --output='': Output format. One of:
json|yaml|name|go-template|go-template-file|template|templatefile|jsonpath|jsonpath-as-json|jsonpath-file.
--save-config=false: If true, the configuration of current object will be saved in its annotation. Otherwise, the
annotation will be unchanged. This flag is useful when you want to perform kubectl apply on this object in the future.
--show-managed-fields=false: If true, keep the managedFields when printing objects in JSON or YAML format.
--template='': Template string or path to template file to use when -o=go-template, -o=go-template-file. The
template format is golang templates [http://golang.org/pkg/text/template/#pkg-overview].
--validate=true: If true, use a schema to validate the input before sending it
Usage:
kubectl create job NAME --image=image [--from=cronjob/name] -- [COMMAND] [args...] [options]
Use "kubectl options" for a list of global command-line options (applies to all commands).
lab@k8s1:~$
lab@k8s1:~$ cat job.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
lab@k8s1:~$
lab@k8s1:~$ kubectl create -f job.yaml
job.batch/pi created
lab@k8s1:~$
lab@k8s1:~$ kubectl get job
NAME COMPLETIONS DURATION AGE
pi 0/1 4s 4s
lab@k8s1:~$ kubectl get job
NAME COMPLETIONS DURATION AGE
pi 0/1 6s 6s
lab@k8s1:~$ kubectl get job
NAME COMPLETIONS DURATION AGE
pi 0/1 7s 7s
lab@k8s1:~$ kubectl get job
NAME COMPLETIONS DURATION AGE
pi 1/1 36s 44s
lab@k8s1:~$
lab@k8s1:~$ kubectl describe job
Name: pi
Namespace: default
Selector: controller-uid=b2835c58-d4fd-4d9f-b715-b26fdecd2c19
Labels: controller-uid=b2835c58-d4fd-4d9f-b715-b26fdecd2c19
job-name=pi
Annotations: <none>
Parallelism: 1
Completions: 1
Completion Mode: NonIndexed
Start Time: Fri, 01 Apr 2022 02:16:45 -0700
Completed At: Fri, 01 Apr 2022 02:17:21 -0700
Duration: 36s
Pods Statuses: 0 Running / 1 Succeeded / 0 Failed
Pod Template:
Labels: controller-uid=b2835c58-d4fd-4d9f-b715-b26fdecd2c19
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 58s job-controller Created pod: pi--1-vb4sm
Normal Completed 22s job-controller Job completed
lab@k8s1:~$
lab@k8s1:~$ kubectl describe pod pi--1-vb4sm
Name: pi--1-vb4sm
Namespace: default
Priority: 0
Node: k8s3/10.210.40.175
Start Time: Fri, 01 Apr 2022 02:16:45 -0700
Labels: controller-uid=b2835c58-d4fd-4d9f-b715-b26fdecd2c19
job-name=pi
Annotations: <none>
Status: Succeeded
IP: 10.244.3.15
IPs:
IP: 10.244.3.15
Controlled By: Job/pi
Containers:
pi:
Container ID: docker://2fb0c18484eaa3eb211fc7ce480764101f08b835df12630083114e160de35f29
Image: perl
Image ID: docker-pullable://perl@sha256:e85f67a5e83029c49a4ce2a91fbfd86a4073d1d2c171a3fa8957d0d5f52a975c
Port: <none>
Host Port: <none>
Command:
perl
-Mbignum=bpi
-wle
print bpi(2000)
State: Terminated
Reason: Completed
Exit Code: 0
Started: Fri, 01 Apr 2022 02:17:16 -0700
Finished: Fri, 01 Apr 2022 02:17:20 -0700
Ready: False
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-kwcz6 (ro)
Conditions:
Type Status
Initialized True
Ready False
ContainersReady False
PodScheduled True
Volumes:
kube-api-access-kwcz6:
Type: Projected (a volume that contains injected data from multiple sources)
TokenExpirationSeconds: 3607
ConfigMapName: kube-root-ca.crt
ConfigMapOptional: <nil>
DownwardAPI: true
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 4m54s default-scheduler Successfully assigned default/pi--1-vb4sm to k8s3
Normal Pulling 4m53s kubelet Pulling image "perl"
Normal Pulled 4m24s kubelet Successfully pulled image "perl" in 28.584816314s
Normal Created 4m24s kubelet Created container pi
Normal Started 4m23s kubelet Started container pi
lab@k8s1:~$
lab@k8s1:~$ kubectl delete jobs pi
job.batch "pi" deleted
lab@k8s1:~$ kubectl get jobs
No resources found in default namespace.
lab@k8s1:~$
Re-create the Job again.
lab@k8s1:~$ kubectl create -f job.yaml
job.batch/pi created
lab@k8s1:~$
lab@k8s1:~$ kubectl get jobs
NAME COMPLETIONS DURATION AGE
pi 1/1 8s 14s
lab@k8s1:~$ kubectl get pods pi--1-hdwp2
NAME READY STATUS RESTARTS AGE
pi--1-hdwp2 0/1 Completed 0 27s
lab@k8s1:~$
lab@k8s1:~$ kubectl logs pi--1-hdwp2
3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113305305488204665213841469519415116094330572703657595919530921861173819326117931051185480744623799627495673518857527248912279381830119491298336733624406566430860213949463952247371907021798609437027705392171762931767523846748184676694051320005681271452635608277857713427577896091736371787214684409012249534301465495853710507922796892589235420199561121290219608640344181598136297747713099605187072113499999983729780499510597317328160963185950244594553469083026425223082533446850352619311881710100031378387528865875332083814206171776691473035982534904287554687311595628638823537875937519577818577805321712268066130019278766111959092164201989380952572010654858632788659361533818279682303019520353018529689957736225994138912497217752834791315155748572424541506959508295331168617278558890750983817546374649393192550604009277016711390098488240128583616035637076601047101819429555961989467678374494482553797747268471040475346462080466842590694912933136770289891521047521620569660240580381501935112533824300355876402474964732639141992726042699227967823547816360093417216412199245863150302861829745557067498385054945885869269956909272107975093029553211653449872027559602364806654991198818347977535663698074265425278625518184175746728909777727938000816470600161452491921732172147723501414419735685481613611573525521334757418494684385233239073941433345477624168625189835694855620992192221842725502542568876717904946016534668049886272327917860857843838279679766814541009538837863609506800642251252051173929848960841284886269456042419652850222106611863067442786220391949450471237137869609563643719172874677646575739624138908658326459958133904780275901
lab@k8s1:~$
lab@k8s1:~$ kubectl delete pods pi--1-hdwp2
pod "pi--1-hdwp2" deleted
lab@k8s1:~$ kubectl get job
NAME COMPLETIONS DURATION AGE
pi 1/1 8s 2m10s
lab@k8s1:~
CronJobs
A CronJob creates Jobs on a repeating schedule.
lab@k8s1:~$ kubectl create cronjob -h
Create a cron job with the specified name.
Aliases:
cronjob, cj
Examples:
# Create a cron job
kubectl create cronjob my-job --image=busybox --schedule="*/1 * * * *"
# Create a cron job with a command
kubectl create cronjob my-job --image=busybox --schedule="*/1 * * * *" -- date
Options:
--allow-missing-template-keys=true: If true, ignore any errors in templates when a field or map key is missing in
the template. Only applies to golang and jsonpath output formats.
--dry-run='none': Must be "none", "server", or "client". If client strategy, only print the object that would be
sent, without sending it. If server strategy, submit server-side request without persisting the resource.
--field-manager='kubectl-create': Name of the manager used to track field ownership.
--image='': Image name to run.
-o, --output='': Output format. One of:
json|yaml|name|go-template|go-template-file|template|templatefile|jsonpath|jsonpath-as-json|jsonpath-file.
--restart='': job's restart policy. supported values: OnFailure, Never
--save-config=false: If true, the configuration of current object will be saved in its annotation. Otherwise, the
annotation will be unchanged. This flag is useful when you want to perform kubectl apply on this object in the future.
--schedule='': A schedule in the Cron format the job should be run with.
--show-managed-fields=false: If true, keep the managedFields when printing objects in JSON or YAML format.
--template='': Template string or path to template file to use when -o=go-template, -o=go-template-file. The
template format is golang templates [http://golang.org/pkg/text/template/#pkg-overview].
--validate=true: If true, use a schema to validate the input before sending it
Usage:
kubectl create cronjob NAME --image=image --schedule='0/5 * * * ?' -- [COMMAND] [args...] [flags] [options]
Use "kubectl options" for a list of global command-line options (applies to all commands).
lab@k8s1:~$
lab@k8s1:~$ cat cronjob.yaml
apiVersion: batch/v1
kind: CronJob
metadata:
name: hello
spec:
schedule: "* * * * *"
jobTemplate:
spec:
template:
spec:
containers:
- name: hello
image: busybox:1.28
imagePullPolicy: IfNotPresent
command:
- /bin/sh
- -c
- date; echo Hello from the Kubernetes cluster
restartPolicy: OnFailure
lab@k8s1:~$
This example CronJob manifest prints the current time and a hello message every minute:
lab@k8s1:~$ kubectl create -f cronjob.yaml
cronjob.batch/hello created
lab@k8s1:~$
lab@k8s1:~$ kubectl get cronjob
NAME SCHEDULE SUSPEND ACTIVE LAST SCHEDULE AGE
hello * * * * * False 0 <none> 5s
lab@k8s1:~$ kubectl describe cronjob
Name: hello
Namespace: default
Labels: <none>
Annotations: <none>
Schedule: * * * * *
Concurrency Policy: Allow
Suspend: False
Successful Job History Limit: 3
Failed Job History Limit: 1
Starting Deadline Seconds: <unset>
Selector: <unset>
Parallelism: <unset>
Completions: <unset>
Pod Template:
Labels: <none>
Containers:
hello:
Image: busybox:1.28
Port: <none>
Host Port: <none>
Command:
/bin/sh
-c
date; echo Hello from the Kubernetes cluster
Environment: <none>
Mounts: <none>
Volumes: <none>
Last Schedule Time: Fri, 01 Apr 2022 02:33:00 -0700
Active Jobs: <none>
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal SuccessfulCreate 23s cronjob-controller Created job hello-27480093
Normal SawCompletedJob 19s cronjob-controller Saw completed job: hello-27480093, status: Complete
lab@k8s1:~$
After some more time,
lab@k8s1:~$ kubectl describe cronjob
Name: hello
Namespace: default
Labels: <none>
Annotations: <none>
Schedule: * * * * *
Concurrency Policy: Allow
Suspend: False
Successful Job History Limit: 3
Failed Job History Limit: 1
Starting Deadline Seconds: <unset>
Selector: <unset>
Parallelism: <unset>
Completions: <unset>
Pod Template:
Labels: <none>
Containers:
hello:
Image: busybox:1.28
Port: <none>
Host Port: <none>
Command:
/bin/sh
-c
date; echo Hello from the Kubernetes cluster
Environment: <none>
Mounts: <none>
Volumes: <none>
Last Schedule Time: Fri, 01 Apr 2022 02:38:00 -0700
Active Jobs: <none>
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal SuccessfulCreate 5m57s cronjob-controller Created job hello-27480093
Normal SawCompletedJob 5m53s cronjob-controller Saw completed job: hello-27480093, status: Complete
Normal SuccessfulCreate 4m57s cronjob-controller Created job hello-27480094
Normal SawCompletedJob 4m56s cronjob-controller Saw completed job: hello-27480094, status: Complete
Normal SuccessfulCreate 3m57s cronjob-controller Created job hello-27480095
Normal SawCompletedJob 3m56s cronjob-controller Saw completed job: hello-27480095, status: Complete
Normal SuccessfulCreate 2m57s cronjob-controller Created job hello-27480096
Normal SuccessfulDelete 2m56s cronjob-controller Deleted job hello-27480093
Normal SawCompletedJob 2m56s cronjob-controller Saw completed job: hello-27480096, status: Complete
Normal SuccessfulCreate 117s cronjob-controller Created job hello-27480097
Normal SawCompletedJob 116s cronjob-controller Saw completed job: hello-27480097, status: Complete
Normal SuccessfulDelete 116s cronjob-controller Deleted job hello-27480094
Normal SuccessfulCreate 57s cronjob-controller Created job hello-27480098
Normal SawCompletedJob 56s cronjob-controller Saw completed job: hello-27480098, status: Complete
Normal SuccessfulDelete 56s cronjob-controller Deleted job hello-27480095
lab@k8s1:~$
We can see every minute, a new job gets created, and hence a new pod as well. But from the jobs list, we see only the latest 3 jobs.
lab@k8s1:~$ kubectl get jobs
NAME COMPLETIONS DURATION AGE
hello-27480097 1/1 1s 2m21s
hello-27480098 1/1 1s 81s
hello-27480099 1/1 1s 21s
pi 1/1 8s 14m
lab@k8s1:~$
Similarly, there are only three latest Pods.
lab@k8s1:~$ kubectl get pods
NAME READY STATUS RESTARTS AGE
hello-27480097--1-rqzxj 0/1 Completed 0 2m44s
hello-27480098--1-lkj9b 0/1 Completed 0 104s
hello-27480099--1-nsqpw 0/1 Completed 0 44s
web-79d88c97d6-4w4nl 1/1 Running 0 2d15h
web-79d88c97d6-7ktck 1/1 Running 0 2d15h
web-79d88c97d6-8tvsk 1/1 Running 0 2d15h
web-79d88c97d6-96sd9 1/1 Running 0 2d15h
web-79d88c97d6-9tzlh 1/1 Running 0 2d15h
web-79d88c97d6-brtgx 1/1 Running 0 2d15h
web-79d88c97d6-kngc4 1/1 Running 0 2d15h
web-79d88c97d6-p5vfg 1/1 Running 0 2d15h
web-79d88c97d6-rbhpr 1/1 Running 0 2d15h
lab@k8s1:~$
We can look at logs from these pods.
lab@k8s1:~$ kubectl logs hello-27480098--1-lkj9b
Fri Apr 1 09:38:01 UTC 2022
Hello from the Kubernetes cluster
lab@k8s1:~$
lab@k8s1:~$ kubectl logs hello-27480099--1-nsqpw
Fri Apr 1 09:39:01 UTC 2022
Hello from the Kubernetes cluster
lab@k8s1:~$
lab@k8s1:~$ kubectl delete cronjob hello
cronjob.batch "hello" deleted
lab@k8s1:~$ kubectl get job
NAME COMPLETIONS DURATION AGE
pi 1/1 8s 21m
lab@k8s1:~$ kubectl get cronjob
No resources found in default namespace.
lab@k8s1:~$ kubectl delete job pi
job.batch "pi" deleted
lab@k8s1:~$
lab@k8s1:~$ kubectl get cronjob,job
No resources found in default namespace.
lab@k8s1:~$
This concludes our discussion on Kubernetes Jobs and CronJobs.
