Jobs & CronJobs

  • * * * * * โ†’ every minute (runs 60 times in an hour).
  • */1 * * * * โ†’ every minute (runs 60 times in an hour). ## more accurate
  • */30 * * * * โ†’ every 30 minute (runs 2 times in an hour).
  • 0 * * * * โ†’ every hour at minute 0 (runs once per hour, exactly on the hour).

๐Ÿ”น 0 0 * * 0

  • First 0 โ†’ minute 0
  • Second 0 โ†’ hour 0 (midnight)
  • * โ†’ any day of month
  • * โ†’ any month
  • Last 0 โ†’ Sunday (in cron, Sunday = 0 or 7)

โœ… This means: run once, exactly at 00:00 (midnight) on Sunday.

๐Ÿ”น * 0 * * 0

  • First * โ†’ every minute (0โ€“59)
  • Second 0 โ†’ hour 0 (midnight)
  • Last 0 โ†’ Sunday

โŒ This means: run every minute between 00:00 and 00:59 on Sunday (so 60 times in that hour).

๐Ÿ‘‰ Thatโ€™s why 0 0 * * 0 is the correct one for โ€œevery Sunday at midnightโ€.

Q1

cka-pod pod exposed internally within the service name cka-service and for cka-pod monitor(access through svc) purpose deployed cka-cronjob cronjob that run every minute. Now cka-cronjob cronjob not working as expected, fix that issue.

controlplane:~$ k get cj
NAME          SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
cka-cronjob   * * * * *   <none>     False     1        5s              56s
controlplane:~$ k get cj
NAME          SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
cka-cronjob   * * * * *   <none>     False     1        37s             88s
controlplane:~$ k get cj
NAME          SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
cka-cronjob   * * * * *   <none>     False     1        55s             106s
controlplane:~$ k get po
NAME                         READY   STATUS             RESTARTS      AGE
cka-cronjob-29272464-8hvj8   0/1     CrashLoopBackOff   4 (46s ago)   2m18s
cka-cronjob-29272465-97fqf   0/1     CrashLoopBackOff   3 (29s ago)   78s
cka-cronjob-29272466-d89vl   0/1     CrashLoopBackOff   1 (15s ago)   18s

controlplane:~$ k describe pod cka-cronjob-29272465-97fqf 
Name:             cka-cronjob-29272465-97fqf
Events:
  Type     Reason     Age                   From               Message
  ----     ------     ----                  ----               -------
  Normal   Started    78s (x5 over 2m48s)   kubelet            Started container curl-container
  Warning  BackOff    12s (x13 over 2m46s)  kubelet            Back-off restarting failed container curl-container in pod cka-cronjob-29272465-97fqf_default(60ee7211-185e-498b-9bc1-0d714d8dc353)
controlplane:~$ k logs cka-cronjob-29272465-97fqf
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0curl: (6) Could not resolve host: cka-pod # wrong host name

controlplane:~$ k edit cj cka-cronjob 
cronjob.batch/cka-cronjob edited

controlplane:~$ k get -o yaml cj cka-cronjob 
apiVersion: batch/v1
kind: CronJob
metadata:
  name: cka-cronjob
          - command:
            - curl
            - cka-pod                      # change it, the host name is cka-service, not cka-pod
            image: curlimages/curl:latest

controlplane:~$ k run test --image curlimages/curl:latest -it -- sh
If you don't see a command prompt, try pressing enter.
~ $ curl cka-service
curl: (7) Failed to connect to cka-service port 80 after 0 ms: Could not connect to server # it's pinging on port 80 mentioned in svc, but no response
~ $ curl cka-service:80
curl: (7) Failed to connect to cka-service port 80 after 0 ms: Could not connect to server
~ $ curl cka-pod
curl: (6) Could not resolve host: cka-pod
~ $ curl cka-service                                # k label po cka-pod app=cka-pod fired from Tab2
<!DOCTYPE html>
<title>Welcome to nginx!</title>
<p><em>Thank you for using nginx.</em></p>
~ $ 


controlplane:~$ k describe po cka-pod 
Name:             cka-pod
    Image:          nginx:latest
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Thu, 28 Aug 2025 02:23:18 +0000
    Ready:          True
    Restart Count:  0

controlplane:~$ k describe svc cka-service 
Name:                     cka-service

Selector:                 app=cka-pod
Type:                     ClusterIP
IP Family Policy:         SingleStack
IP Families:              IPv4
IP:                       10.107.195.27
IPs:                      10.107.195.27
Port:                     <unset>  80/TCP
TargetPort:               80/TCP
Endpoints:                                                    # culprit
controlplane:~$ k label po cka-pod app=cka-pod
pod/cka-pod labeled

controlplane:~$ k get cj cka-cronjob 
NAME          SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
cka-cronjob   * * * * *   <none>     False     0        20s             35m
controlplane:~$ k get po
NAME                         READY   STATUS      RESTARTS   AGE
cka-cronjob-29272496-pfcmd   0/1     Completed   0          2m33s
cka-cronjob-29272497-wftzj   0/1     Completed   0          93s
cka-cronjob-29272498-dmvzh   0/1     Completed   0          33s
cka-pod                      1/1     Running     0          35m
test                         1/1     Running     0          26m
controlplane:~$ k get cj cka-cronjob 
NAME          SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
cka-cronjob   * * * * *   <none>     False     0        58s             35m
controlplane:~$ k get cj cka-cronjob 
NAME          SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
cka-cronjob   * * * * *   <none>     False     0        5s              35m
controlplane:~$ k get po
NAME                         READY   STATUS      RESTARTS   AGE
cka-cronjob-29272497-wftzj   0/1     Completed   0          2m17s
cka-cronjob-29272498-dmvzh   0/1     Completed   0          77s
cka-cronjob-29272499-29r8q   0/1     Completed   0          17s
cka-pod                      1/1     Running     0          36m
test                         1/1     Running     0          26m
controlplane:~$ k describe cj cka-cronjob 
Name:                          cka-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:
   curl-container:
    Image:      curlimages/curl:latest
    Port:       <none>
    Host Port:  <none>
    Command:
      curl
      cka-service
    Environment:     <none>
    Mounts:          <none>
  Volumes:           <none>
  Node-Selectors:    <none>
  Tolerations:       <none>
Last Schedule Time:  Thu, 28 Aug 2025 03:00:00 +0000
Active Jobs:         <none>
Events:
  Type    Reason            Age                  From                Message
  ----    ------            ----                 ----                -------
  Normal  SuccessfulCreate  36m                  cronjob-controller  Created job cka-cronjob-29272464
  Normal  SuccessfulCreate  35m                  cronjob-controller  Created job cka-cronjob-29272465
  Normal  SuccessfulCreate  34m                  cronjob-controller  Created job cka-cronjob-29272466
  Normal  SuccessfulCreate  33m                  cronjob-controller  Created job cka-cronjob-29272467
  Normal  SuccessfulCreate  32m                  cronjob-controller  Created job cka-cronjob-29272468
  Normal  SuccessfulCreate  31m                  cronjob-controller  Created job cka-cronjob-29272469
  Normal  SawCompletedJob   30m                  cronjob-controller  Saw completed job: cka-cronjob-29272464, condition: Failed
  Normal  SuccessfulCreate  30m                  cronjob-controller  Created job cka-cronjob-29272470
  Normal  SuccessfulDelete  29m                  cronjob-controller  Deleted job cka-cronjob-29272464
  Normal  SawCompletedJob   29m                  cronjob-controller  Saw completed job: cka-cronjob-29272465, condition: Failed
  Normal  SuccessfulCreate  29m                  cronjob-controller  Created job cka-cronjob-29272471
  Normal  SawCompletedJob   29m                  cronjob-controller  Saw completed job: cka-cronjob-29272466, condition: Failed
  Normal  SuccessfulDelete  29m                  cronjob-controller  Deleted job cka-cronjob-29272465
  Normal  SuccessfulCreate  28m                  cronjob-controller  Created job cka-cronjob-29272472
  Normal  SuccessfulDelete  28m                  cronjob-controller  Deleted job cka-cronjob-29272466
  Normal  SawCompletedJob   28m                  cronjob-controller  Saw completed job: cka-cronjob-29272467, condition: Failed
  Normal  SawCompletedJob   26m                  cronjob-controller  Saw completed job: cka-cronjob-29272468, condition: Failed
  Normal  SuccessfulDelete  26m                  cronjob-controller  Deleted job cka-cronjob-29272467
  Normal  SuccessfulDelete  25m                  cronjob-controller  Deleted job cka-cronjob-29272468
  Normal  SawCompletedJob   25m                  cronjob-controller  Saw completed job: cka-cronjob-29272469, condition: Failed
  Normal  SuccessfulDelete  24m                  cronjob-controller  Deleted job cka-cronjob-29272469
  Normal  SawCompletedJob   24m                  cronjob-controller  Saw completed job: cka-cronjob-29272470, condition: Failed
  Normal  SuccessfulCreate  24m (x4 over 27m)    cronjob-controller  (combined from similar events): Created job cka-cronjob-29272476
  Normal  SuccessfulDelete  24m                  cronjob-controller  Deleted job cka-cronjob-29272470
  Normal  SuccessfulDelete  103s (x23 over 22m)  cronjob-controller  (combined from similar events): Deleted job cka-cronjob-29272496
controlplane:~$

Q2

Create a job named countdown-devops.

The spec template should be named countdown-devops (under metadata), and the container should be named container-countdown-devops

Utilize image debian with latest tag (ensure to specify as debian:latest), and set the restart policy to Never.

Execute the command sleep 5

thor@jumphost ~$ vi avc.yaml
thor@jumphost ~$ k apply -f avc.yaml 
job.batch/countdown-devops created
thor@jumphost ~$ k get po
NAME                     READY   STATUS    RESTARTS   AGE
countdown-devops-qhwbh   1/1     Running   0          4s
thor@jumphost ~$ cat avc.yaml 
apiVersion: batch/v1
kind: Job
metadata:
  name: countdown-devops
spec:
  template:
    metadata:
      name: countdown-devops   # Pod template name
    spec:
      containers:
      - name: container-countdown-devops
        image: debian:latest
        command: ["sleep", "5"]
      restartPolicy: Never

thor@jumphost ~$

Q3

In the ckad-job namespace, create a cronjob named simple-node-job to run every 30 minutes to list all the running processes inside a container that used node image (the command needs to be run in a shell). In Unix-based operating systems, ps -eaf can be use to list all the running processes.

root@student-node ~ โžœ  k create cj simple-node-job -n ckad-job --schedule "*/30 * * * *" --image node -- sh -c "ps -eaf"
cronjob.batch/simple-node-job created

apiVersion: batch/v1
kind: CronJob
            command:
            - sh
            - -c
            - ps -eaf

Q4

In the ckad-job namespace, create a job named very-long-pi that simply computes a ฯ€ (pi) to 1024 places and prints it out.

This job should be configured to retry maximum 5 times before marking this job failed, and the duration of this job should not exceed 100 seconds.

The job should use the container image perl:5.34.0.

The container should run a Perl command that calculates ฯ€ (pi) to 1024 decimal places using:

perl -Mbignum=bpi -wle 'print bpi(1024)'

root@student-node ~ โžœ  vi 2.yaml

root@student-node ~ โžœ  k apply -f 2.yaml 
job.batch/very-long-pi created

root@student-node ~ โžœ  k get job -n ckad-job 
NAME           STATUS    COMPLETIONS   DURATION   AGE
very-long-pi   Running   0/1           16s        16s

root@student-node ~ โžœ  cat 2.yaml 
apiVersion: batch/v1
kind: Job
metadata:
  name: very-long-pi
  namespace: ckad-job
spec:
  template:
    spec:
      containers:
      - name: pi
        image: perl:5.34.0
        command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(1024)"]
      restartPolicy: Never
  backoffLimit: 5                # retries before marking failed
  activeDeadlineSeconds: 100     # max duration


root@student-node ~ โžœ  k get job -n ckad-job 
NAME           STATUS     COMPLETIONS   DURATION   AGE
very-long-pi   Complete   1/1           20s        46s

Q5

In the ckad-job namespace, schedule a job called learning-every-hour that prints this message in the shell every hour at 0 minutes: I will pass CKAD certification. In case the container in pod failed for any reason, it should be restarted automatically. Use alpine image for the cronjob!

root@student-node ~ โžœ  k create cj learning-every-hour -n ckad-job --image alpine --schedule "* * * * *" -- "echo 'I will pass CKAD certification'" # wrong
cronjob.batch/learning-every-hour created # wrong

root@student-node ~ โžœ  k get cj -n ckad-job 
NAME                  SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
learning-every-hour   * * * * *   <none>     False     1        11s             24s

root@student-node ~ โžœ  k get cj -n ckad-job
NAME                  SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
learning-every-hour   * * * * *   <none>     False     1        41s             54s

root@student-node ~ โžœ  k get cj -n ckad-job
NAME                  SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
learning-every-hour   * * * * *   <none>     False     1        51s             64s

root@student-node ~ โžœ  k get cj -n ckad-job
NAME                  SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
learning-every-hour   * * * * *   <none>     False     2        11s             84s

root@student-node ~ โžœ  k logs -n ckad-job learning-every-hour-2929321
error: error from server (NotFound): pods "learning-every-hour-2929321" not found in namespace "ckad-job"

root@student-node ~ โœ– k logs -n ckad-job learning-every-hour-2929321
error: error from server (NotFound): pods "learning-every-hour-2929321" not found in namespace "ckad-job"

root@student-node ~ โœ– k get po -n ckad-job 
NAME                                 READY   STATUS              RESTARTS      AGE
learning-every-hour-29293210-5dxks   0/1     CrashLoopBackOff    4 (47s ago)   2m15s
learning-every-hour-29293211-4vth7   0/1     CrashLoopBackOff    3 (33s ago)   75s
learning-every-hour-29293212-mrx6f   0/1     RunContainerError   2 (2s ago)    15s

root@student-node ~ โžœ  k edit cj -n ckad-job learning-every-hour 
Edit cancelled, no changes made.

root@student-node ~ โžœ  k delete cj -n ckad-job learning-every-hour 
cronjob.batch "learning-every-hour" deleted

root@student-node ~ โžœ  kubectl create cronjob learning-every-hour \
  --image=alpine \
  --schedule="0 * * * *" \
  --namespace=ckad-job \
  -- /bin/sh -c "echo 'I will pass CKAD certification.'"
cronjob.batch/learning-every-hour created

root@student-node ~ โžœ  k get cj -n ckad-job 
NAME                  SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
learning-every-hour   0 * * * *   <none>     False     0        <none>          16s

root@student-node ~ โžœ  k get cj -n ckad-job 
NAME                  SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
learning-every-hour   0 * * * *   <none>     False     0        <none>          44s

root@student-node ~ โžœ  k get cj -n ckad-job 
NAME                  SCHEDULE    TIMEZONE   SUSPEND   ACTIVE   LAST SCHEDULE   AGE
learning-every-hour   0 * * * *   <none>     False     0        <none>          84s

root@student-node ~ โžœ

Good catch ๐ŸŒŸ

Hereโ€™s the difference:

  • * * * * * โ†’ every minute (runs 60 times in an hour).
  • 0 * * * * โ†’ every hour at minute 0 (runs once per hour, exactly on the hour).

Your task explicitly said:

"every hour at 0 minutes"

So โœ… the correct cron expression is 0 * * * *, not * * * * *.

Nice ๐Ÿ‘Œ this is a subtle but important cron expression detail.

*In the ckad-job namespace, schedule a job called learning-every-minute that prints this message in the shell every minute: I am practicing for CKAD certification.

Perfect โ€” let me explain why the CKAD grader insists on */1 instead of * for โ€œevery minuteโ€:

1๏ธโƒฃ * * * * * vs */1 * * * *

  • * * * * * โ†’ Literally means โ€œevery value of minute, hour, day, month, weekdayโ€ โ†’ works fine in standard Cron.
  • */1 * * * * โ†’ Means โ€œevery 1 minuteโ€ โ†’ also runs every minute.

Functionally, both are identical.

2๏ธโƒฃ Why the grader rejects * * * * *

CKAD exam auto-graders are scripted to check for exact text matches, not the Cron logic itself.

  • If the instructions say:

schedule a job every minute the grader expects */1 * * * * literally in the YAML. * * * * * * will run correctly in Kubernetes, but the grader sees a mismatch in the string value.

3๏ธโƒฃ Practical lesson

  • Always follow the exact syntax requested in CKAD tasks.
  • Logical equivalence doesnโ€™t matter for auto-graders; textual equivalence does.

โœ… So, for CKAD, always write:

schedule: "*/1 * * * *"

Even though * * * * * works in real clusters.

Q6

Create a cronjob called dice that runs every one minute. Use the Pod template located at /root/throw-a-dice. The image throw-dice randomly returns a value between 1 and 6. The result of 6 is considered success and all others are failure.

The job should be non-parallel and complete the task once. Use a backoffLimit of 25.

If the task is not completed within 20 seconds the job should fail and pods should be terminated.

controlplane ~ โžœ  cat throw-a-dice/throw-a-dice.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: throw-dice-pod
spec:
  containers:
  -  image: kodekloud/throw-dice
     name: throw-dice
  restartPolicy: Never

controlplane ~ โžœ  cat 2.yaml 
apiVersion: batch/v1
kind: CronJob
metadata:
  name: dice
spec:
  schedule: "*/1 * * * *"
  jobTemplate:
    spec:
      activeDeadlineSeconds: 20
      backoffLimit: 25
      template:
        metadata:
          name: throw-dice-pod
        spec:
          containers:
          - image: kodekloud/throw-dice
            name: throw-dice
          restartPolicy: Never

controlplane ~ โžœ