k8s-demo

Description

This project contains examples of how to use Helm to deploy a Job and an App with Kubernetes in the comfort of your own local environment using minikube.

These examples aim to provide an introduction to some common use cases and tips for getting started with Kubernetes and Helm. See also Useful Helm commands.

• k8s: Contains examples to create a PersistentVolume, PersistentVolumeClaim, Job, helper Pod, Service, Deployment
• helm: Contains Helm charts for app-demo, job-demo
• app: Contains example code to create a Streamlit app

Prerequistes

• Install minikube >= 1.x
• Install Helm>= 3.x
• Optionally install helm-diff

Check installation:

which minikube

which helm

Job Example

This is an example of a Kubernetes job which writes an output to a volume.

Create storage

The following command will create a PersistentVolume and PersistentVolumeClaim:

kubectl apply -f k8s/volume.yaml

persistentvolume/kt-volume created
persistentvolumeclaim/kt-pvc created

Check out what got created:

kubectl get pv kt-volume

kubectl get pvc kt-pvc

For more information, check out the Kubernetes docs on configuring persistent volume storage.

Run Job with kubectl

The following will run a Kubernetes job which writes to the volume that was previously created:

kubectl apply -f k8s/job.yaml

Check it out:

kubectl get job job-demo

Clean up:

kubectl delete job job-demo

Check out the file

We can use a task pod which uses the PersistentVolumeClaim as a volume.

kubectl apply -f k8s/task_pv_pod.yaml

Get a shell to the container running in the pod:

kubectl exec -it task-pv-pod -- /bin/bash

Check out the file that the job wrote:

cat mnt/data/demo_file.txt

Copy the file that was created:

kubectl cp task-pv-pod:/mnt/data/demo_file.txt demo_file.txt

Clean up:

kubectl delete pod task-pv-pod

Run Job with Helm

We can also use Helm to run the same job. This will make our job easier to customize, such as changing the environment variables, container image, and other job specs.

Install / upgrade job-demo Helm chart with default values:

helm upgrade job-demo helm/job_demo/ -i

Alternatively, install / upgrade job-demo Helm chart overriding values from the command line:

helm upgrade --set env.filename=new_file.txt job-demo helm/job_demo/ -i

Check out the job that got created:

kubectl describe job job-demo

Clean up the job:

kubectl delete job job-demo

To check out the file that updated / created, see Check out the file.

App Example

This is an example of a Kubernetes Service and Deployment for a Streamlit app, which builds on the PV and PVC created in the previous section.

Build

Point your terminal to use the docker daemon inside minikube:

eval $(minikube docker-env)

Build Docker image:

docker build -t kt-app-demo .

Deploy with kubectl

Create the Service and Deployment:

kubectl apply -f k8s/service.yaml

Check out the resources:

kubectl get deployment,service,replicaset -l app=app-demo 

Check out the app

Since we are using spec.type: ClusterIP, we will use port forwarding to access the application in the minikube cluster.

kubectl port-forward deployment/app-demo-deployment 8080:8501

Head over to localhost:8080 to try it out for yourself:

We can interact with the App running in our local cluster in order to write to and read from a file in the mounted volume. Nice!

Clean up:

kubectl delete deployment,services -l app=app-demo 

Deploy App with Helm

We can also use Helm to deploy the Streamlit app. This will make it easier to customize our app, such as changing the environment variables, container image, and other deployment or service specs.

Install / upgrade app-demo Helm chart with default values:

helm upgrade app-demo helm/app_demo/ -i

Check out the resources that got created:

kubectl get deployment,service,replicaset -l app=app-demo

To try out the app in your browser, see Check out the app.

Useful Helm commands

Below are a few commands that are helpful for working with Helm charts.

Render chart template and display the output:

helm template helm/job_demo/ 

with --release-name

helm template --release-name app-demo helm/app_demo

Check the chart for possible issues:

helm lint helm/job_demo/ 

Dry-run chart install / upgrade to check computed values:

helm upgrade job-demo helm/job_demo/ -i --dry-run --debug 

List releases:

helm list

NAME    	NAMESPACE	REVISION	STATUS  	CHART
job-demo	default  	2       	deployed	job-demo-0.1.0	      

Check out everything that was installed with the Helm release:

helm get manifest job-demo

Check out the history of a Helm release:

helm history job-demo

Show what changed in two revisions (requires installing helm-diff):

helm diff revision job-demo 1 2