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Create an Helm Chart

Learning goal

  • Create a basic Helm chart for the sentences application

Introduction

This exercise will create a simple Helm chart for the sentence application. The chart will be 'simple' in the sense that it will not provide support for customizing application parameters.

More information

In the sentences-app/deploy/kubernetes/ folder we have Kubernetes YAML definitions for the three microservices that make up the sentence application (three Deployments and three Services):

$ ls -1 sentences-app/deploy/kubernetes/
sentences-age-deployment.yaml
sentences-age-svc.yaml
sentences-deployment.yaml
sentences-name-deployment.yaml
sentences-name-svc.yaml
sentences-svc.yaml

Exercise

Overview

  • Running the sentences application on Kubernetes
  • Create a skeleton Helm chart
  • Copy sentences kubernetes yaml into the chart
  • Lint and deploy our new chart

Step by step

More details

Deploy the sentences application to Kubernetes

First, let's run the application in bare Kubernetes to see that our YAML is right.

  • kubectl apply -f sentences-app/deploy/kubernetes

This will create three microservice deployments with a single POD instance each.

Test the deployed application

  • kubectl get pods

💡 The front-end microservice for the sentences application is exposed with a Kubernetes service of type NodePort.

When all three PODs are in a running state, look up the actual NodePort used by the frontend microservice:

  • kubectl get svc sentence

Output:

NAME        TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
sentences   NodePort   10.15.245.208   <none>        8080:30250/TCP   37s

In the example above, the relevant NodePort is 30250.

  • look up an external accessible IP address that can be used to access the front-end microservice.

  • kubectl get nodes -o wide

Any of the IP addresses from the EXTERNAL-IP-column can be used.

To request a sentence from the sentences application, use curl with the external IP address and NodePort found above:

  • curl <EXTERNAL-IP>:<NodePort>

Output:

John is 73 years

💡 in the above example NodePort should be changed with your nodeport found above

  • Clean up the application deployed with kubectl delete -f sentences-app/deploy/kubernetes/

Create a skeleton Helm chart

First we create a new directory for our Helm chart, and then use the helm create command to create the chart skeleton:

  • mkdir helm-chart
  • cd helm-chart
  • helm create sentence-app

The helm create command we just issued created a lot of files that you might want to use when creating a new Helm chart. We do not need all of those files for the chart we will be creating, therefore we will remove the files we do not need:

  • rm -rf sentence-app/templates/*
  • echo "" > sentence-app/values.yaml

This provides us with skeleton chart without any template files.

Copy sentences kubernetes yaml into the chart

Next, we copy the original Kubernetes YAML files to the template folder:

  • cp -v ../sentences-app/deploy/kubernetes/*.yaml sentence-app/templates/

That's it - now we have a Helm chart for our sentences application.

💡 It is a simple Helm chart in the sense that it has no configurable values, but it is a complete installable chart and it will use the correct sentence application Kubernetes YAML definitions.

Lint and deploy our new chart

Before deploying the chart, we run a static validation of it:

  • helm lint sentence-app/

Running this command produces the following output:

==> Linting sentence-app/
[INFO] Chart.yaml: icon is recommended

1 chart(s) linted, 0 chart(s) failed

💡 Normally a chart is fetched from a chart registry (like a container registry), however, a chart stored locally can also be deployed with Helm.

To deploy the chart from the newly created chart run the following:

helm install sentences sentence-app/

Running this command produces the following output:

NAME: sentences
LAST DEPLOYED: Wed Apr 21 10:43:55 2021
NAMESPACE: user1
STATUS: deployed
REVISION: 1
TEST SUITE: None

To see all the different objects that Helm has created, use:

kubectl get pods,services,deployments

Expected output:

NAME                                READY   STATUS    RESTARTS   AGE
pod/sentence-age-78fc854dd5-w9gdq   1/1     Running   0          64s
pod/sentence-name-ff4c584b9-txp5n   1/1     Running   0          64s
pod/sentences-746cc46db8-khp85      1/1     Running   0          64s

NAME               TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)          AGE
service/age        ClusterIP   10.191.240.60    <none>        8080/TCP         66s
service/name       ClusterIP   10.191.251.238   <none>        8080/TCP         66s
service/sentence   NodePort    10.191.245.72    <none>        8080:32665/TCP   66s

NAME                            READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/sentence-age    1/1     1            1           66s
deployment.apps/sentence-name   1/1     1            1           66s
deployment.apps/sentences       1/1     1            1           66s

To see the applications installed with Helm use the helm ls operation:

helm ls

expected output:

NAME            NAMESPACE       REVISION        UPDATED                                 STATUS         CHART                    APP VERSION
sentences       user1           1               2021-04-21 10:43:55.789048706 +0000 UTC deployed       sentence-app-0.1.0       1.16.0

To see the Kubernetes YAML which Helm used to install the application use the helm get operation:

helm get all sentences

In our case this will be identical to the YAML files we copied previously since we haven't provided any means of customizing the application installation.

Try to reach it again like we did with the raw kubernetes objects application to begin with.

  • Note down the NodePort from the service kubectl get svc

Look up an external accessible IP address that can be used to access the front-end microservice.

  • kubectl get nodes -o wide

Any of the IP addresses from the EXTERNAL-IP-column can be used.

  • curl <EXTERNAL-IP>:<NodePort> and see that your application is running once again.

Output:

John is 47 years

Food for Thought

In this exercise we created a single Helm chart for the complete application even though it is based on three microservices. When would it make sense to have a Helm chart for each microservice?

Cleanup

Uninstall the application release with Helm:

helm uninstall sentences