Add cronjob

08-cronjob/01-simple-cronjob.yml

@@ -0,0 +1,15 @@
+apiVersion: batch/v1beta1
+kind: CronJob
+metadata:
+  name: simple-cronjob
+spec:
+  schedule: "*/1 * * * *"
+  jobTemplate:
+    spec:
+      template:
+        spec:
+          restartPolicy: Never
+          containers:
+          - name: pi
+            image: perl
+            command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(100)"]

08-cronjob/02-simple-job.yml

@@ -0,0 +1,12 @@
+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: simple-job
+spec:
+  template:
+    spec:
+      containers:
+      - name: c
+        image: busybox
+        command: ["sh", "-c", "echo Processing item $ITEM && sleep 5"]
+      restartPolicy: Never

08-cronjob/README.md

@@ -1,3 +1,74 @@
 # Running a background process: `cronjob`
 
-In this section you will lean how to run background tasks using crons & deployments.
+In this section you will lean how to run background tasks using crons & deployments.
+
+Let's start with crons. Crons are like the cron in linux a time-based job scheduler.
+
+```yml
+apiVersion: batch/v1beta1
+kind: CronJob
+metadata:
+  name: simple-cronjob
+spec:
+  schedule: "*/1 * * * *"
+  jobTemplate:
+    spec:
+      template:
+        spec:
+          restartPolicy: Never
+          containers:
+          - name: pi
+            image: perl
+            command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(100)"]
+```
+
+* `spec`:
+  * `schedule`: when to start this cron, in the same format as the linux crons. `*/2 * * * *` means every minute
+  * `jobTemplate`: the template of the container(s) to start
+    * `command`: the command to run, here compute the first 100 digits of π.
+
+Let's apply it:
+```bash
+$ kubectl apply -f 08-cronjob/01-simple-cronjob.yml
+cronjob.batch "simple-cronjob" created
+```
+
+Wait a bit and access the logs of the pod created by the cron.
+
+If you need to run a one time job, you can use the `Job` in kubernetes. In fact the `CronJob` will start a `Job` for you at the scheduled interval.
+
+```yml
+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: simple-job
+spec:
+  template:
+    spec:
+      containers:
+      - name: c
+        image: busybox
+        command: ["sh", "-c", "echo Processing item $ITEM && sleep 5"]
+      restartPolicy: Never
+```
+
+They configuration is fairly close to a `CronJob`.
+
+Apply it and see what is happening. Does it restarts?
+```bash
+$ kubectl apply -f 08-cronjob/02-simple-job.yml
+job.batch "simple-job" created
+```
+
+If you have a long running background process - like a consumer of a queue - you can use a `deployment` without a `service`.
+
+## Exercices
+
+1. Transform the `simple-job` to a cron job running every 2 minutes
+2. Transform the `simple-cronjob` in a deployment of `1` replica, and compute the 1_000 first digits of π. What is happening when the container finishes?
+
+## Clean up
+
+```bash
+$ kubectl delete deployment,rs,service,cronjob,pod --all
+```