Day 12/40
Kubernetes Daemonset Explained - Daemonsets, Job and Cronjob in Kubernetes
Video Link
@piyushsachdeva
Git Repository
My Git Repo
This section is about cronjob, job and daemonset.
As the definition, DaemonSets are Kubernetes API objects that allow you to run Pods as a daemon on each of your Nodes. New Nodes that join the cluster will automatically start running Pods that are part of a DaemonSet.
DaemonSets are often used to run long-lived background services such as Node monitoring systems and log collection agents. To ensure complete coverage, it’s important that these apps run a Pod on every Node in your cluster. source
1. Create a daemonset:
apiVersion: apps/v1
kind: DaemonSet
metadata:
name: nginx-ds
labels:
env: demo
spec:
template:
metadata:
labels:
env: demo
name: nginx
spec:
containers:
- image: nginx
name: nginx
ports:
- containerPort: 80
selector:
matchLabels:
env: demo
root@localhost:~# kubectl apply -f daemonset.yaml
daemonset.apps/nginx-ds created
root@localhost:~# kubectl get po
NAME READY STATUS RESTARTS AGE
nginx-ds-mf4gz 1/1 Running 0 11s
nginx-ds-rslrm 1/1 Running 0 11s
root@localhost:~# kubectl get po -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-ds-mf4gz 1/1 Running 0 19s 10.244.2.9 lucky-luke-worker2 <none> <none>
nginx-ds-rslrm 1/1 Running 0 19s 10.244.1.12 lucky-luke-worker <none> <none>
As you can see, our custom workload as daemonset is running on all worker nodes and because it is not a control-plane component and the control-plane node doesn't tolerate custom workload, it doesn't run on control-plane node. (but we can change it)
If one of these pod removed, it will run another one on that node
root@localhost:~# kubectl get po
NAME READY STATUS RESTARTS AGE
nginx-ds-mf4gz 1/1 Running 0 9m40s
nginx-ds-rslrm 1/1 Running 0 9m40s
root@localhost:~# kubectl delete pod nginx-ds-mf4gz
pod "nginx-ds-mf4gz" deleted
root@localhost:~# kubectl get po
NAME READY STATUS RESTARTS AGE
nginx-ds-946m4 1/1 Running 0 5s
nginx-ds-rslrm 1/1 Running 0 10m
- See all
daemonseton ourcluster:
root@localhost:~# kubectl get ds --all-namespaces
NAMESPACE NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE SELECTOR AGE
default nginx-ds 2 2 2 2 2 <none> 10m
kube-system kindnet 3 3 3 3 3 kubernetes.io/os=linux 3d
kube-system kube-proxy 3 3 3 3 3 kubernetes.io/os=linux 3d
2. Cronjobs
See the Cronitor website for understand how it can be configured for tasks run in specific time.
(Photo from the video)
- Sample from
Kuberneteswebsite:
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
3. 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. 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. Suspending a Job will delete its active Pods until the Job is resumed again. source
- Sample from
Kuberneteswebsite
apiVersion: batch/v1
kind: Job
metadata:
name: pi
spec:
template:
spec:
containers:
- name: pi
image: perl:5.34.0
command: ["perl", "-Mbignum=bpi", "-wle", "print bpi(2000)"]
restartPolicy: Never
backoffLimit: 4
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