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lab-16/README.md

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+# Lab 16 - Jobs / Cronjobs
+
+## Jobs
+
+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.
+
+## Task 0: Creating a namespace
+
+Create a namespace for this lab:
+
+```
+kubectl create ns lab-19
+
+---
+
+namespace "lab-19" created
+```
+
+## Task 1: Running an example Job
+
+Here is an example Job config. It computes π to 2000 places and prints it out. 
+It takes around 10s to complete.
+
+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
+```
+
+Now let’s run `kubectl create -f job.yaml -n lab-19` to deploy the example.
+
+## Task 2: Check the status of the job
+
+```
+kubectl describe jobs/pi
+
+---
+
+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`.
+
+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 --selector=job-name=pi --output=jsonpath='{.items[*].metadata.name}')
+echo $pods
+
+kubectl logs $pods
+
+3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113305305488204665213841469519415116094330572703657595919530921861173819326117931051185480744623799627495673518857527248912279381830119491298336733624406566430860213949463952247371907021798609437027705392171762931767523846748184676694051320005681271452635608277857713427577896091736371787214684409012249534301465495853710507922796892589235420199561121290219608640344181598136297747713099605187072113499999983729780499510597317328160963185950244594553469083026425223082533446850352619311881710100031378387528865875332083814206171776691473035982534904287554687311595628638823537875937519577818577805321712268066130019278766111959092164201989380952572010654858632788659361533818279682303019520353018529689957736225994138912497217752834791315155748572424541506959508295331168617278558890750983817546374649393192550604009277016711390098488240128583616035637076601047101819429555961989467678374494482553797747268471040475346462080466842590694912933136770289891521047521620569660240580381501935112533824300355876402474964732639141992726042699227967823547816360093417216412199245863150302861829745557067498385054945885869269956909272107975093029553211653449872027559602364806654991198818347977535663698074265425278625518184175746728909777727938000816470600161452491921732172147723501414419735685481613611573525521334757418494684385233239073941433345477624168625189835694855620992192221842725502542568876717904946016534668049886272327917860857843838279679766814541009538837863609506800642251252051173929848960841284886269456042419652850222106611863067442786220391949450471237137869609563643719172874677646575739624138908658326459958133904780275901
+```
+
+### Job Termination and Cleanup
+
+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 ./job.yaml). When you delete 
+the job using kubectl, all the pods it created are deleted too.
+
+## Cronjob
+
+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.
+
+## Task 3: Creating a Cron Job
+
+Cron jobs require a config file. This example cron job config .spec file prints 
+the current time and a hello message every minute:
+
+Create the following cronjob.yaml file:
+
+```
+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
+```
+
+After creating the cron job, get its status using this command:
+
+```
+kubectl get cronjob hello
+```
+
+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
+```
+
+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 --selector=job-name=hello-4111706356 --output=jsonpath={.items[].metadata.name})
+```
+
+Show pod log:
+
+```
+kubectl logs $pods
+
+Tue Aug 27 12:58:07 UTC 2019
+Hello from the Kubernetes cluster
+```
+
+Delete the Cron Job
+
+```
+kubectl delete cronjob hello
+```
+
+## Task 4: Cleaning up
+
+In order to delete our daemonset use the following command:
+
+```
+kubectl delete ns lab-19
+
+---
+
+namespace "lab-19" deleted
+```