3 min read | by Jordi Prats
The cronjob object haven't been GA until Kubernetes v1.21, even though the Job object have been GA for a long time. Let's take a look how it works:
$ kubectl create job demo --image nginx --dry-run=client -o yaml | head -n1 apiVersion: batch/v1 $ kubectl create cronjob demo --image nginx --schedule="*/1 * * * *" -o yaml --dry-run=client | head -n1 apiVersion: batch/v1beta1 Using the kubectl we get how a cronjob yaml will look like. It is quite similar a what a deployment is since it has a spec.template that is also used for creating the actual pods that will actually execute the job:
$ kubectl create cronjob my-cronjob --image=busybox --schedule="*/1 * * * *" -o yaml --dry-run=client -- echo test apiVersion: batch/v1beta1 kind: CronJob metadata: creationTimestamp: null name: my-cronjob spec: jobTemplate: metadata: creationTimestamp: null name: my-cronjob spec: template: metadata: creationTimestamp: null spec: containers: - command: - echo - test image: busybox name: my-cronjob resources: {} restartPolicy: OnFailure schedule: '*/1 * * * *' status: {} Let's create an simple cronjob to check how it executes the job:
$ kubectl create cronjob demo-cronjob --image=busybox --schedule="* * * * *" -- echo test cronjob.batch/demo-cronjob created After waiting for a while we will be able to see the executions on the events section of a kubectl describe:
$ kubectl describe cronjob demo-cronjob Name: demo-cronjob 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: demo-cronjob: Image: busybox Port: <none> Host Port: <none> Command: echo test Environment: <none> Mounts: <none> Volumes: <none> Last Schedule Time: Tue, 05 Jan 2021 21:07:00 +0100 Active Jobs: <none> Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal SuccessfulCreate 3m19s cronjob-controller Created job demo-cronjob-1609866240 Normal SawCompletedJob 2m58s cronjob-controller Saw completed job: demo-cronjob-1609866240, status: Complete Normal SuccessfulCreate 2m18s cronjob-controller Created job demo-cronjob-1609866300 Normal SawCompletedJob 2m7s cronjob-controller Saw completed job: demo-cronjob-1609866300, status: Complete Normal SuccessfulCreate 77s cronjob-controller Created job demo-cronjob-1609866360 Normal SawCompletedJob 67s cronjob-controller Saw completed job: demo-cronjob-1609866360, status: Complete Normal SuccessfulCreate 16s cronjob-controller Created job demo-cronjob-1609866420 Normal SawCompletedJob 5s cronjob-controller Saw completed job: demo-cronjob-1609866420, status: Complete Normal SuccessfulDelete 5s cronjob-controller Deleted job demo-cronjob-1609866240 To be able to get the execution log we will have to first describe the job that gets created:
$ kubectl describe job demo-cronjob-1609866420 Name: demo-cronjob-1609866420 Namespace: default Selector: controller-uid=81e2745e-0a73-49fa-8f01-890f9dafebda Labels: controller-uid=81e2745e-0a73-49fa-8f01-890f9dafebda job-name=demo-cronjob-1609866420 Annotations: <none> Controlled By: CronJob/demo-cronjob Parallelism: 1 Completions: 1 Start Time: Tue, 05 Jan 2021 21:07:06 +0100 Completed At: Tue, 05 Jan 2021 21:07:13 +0100 Duration: 7s Pods Statuses: 0 Running / 1 Succeeded / 0 Failed Pod Template: Labels: controller-uid=81e2745e-0a73-49fa-8f01-890f9dafebda job-name=demo-cronjob-1609866420 Containers: demo-cronjob: Image: busybox Port: <none> Host Port: <none> Command: echo test Environment: <none> Mounts: <none> Volumes: <none> Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal SuccessfulCreate 2m20s job-controller Created pod: demo-cronjob-1609866420-f4dv7 Normal Completed 2m14s job-controller Job completed Then we can use kubectl logs to get the output of the pod that this cronjob creates, again we can see it on the events section:
$ kubectl logs demo-cronjob-1609866420-f4dv7 test Posted on 20/01/2021