Helm Chart ¶

Install Helm ¶

Install Helm on cka001.

# https://github.com/helm/helm/releases
wget https://get.helm.sh/helm-v3.8.2-linux-amd64.tar.gz
tar -zxvf helm-v3.8.2-linux-amd64.tar.gz
cp linux-amd64/helm /usr/bin/
rm -rf linux-amd64 helm-v3.8.2-linux-amd64.tar.gz

Or manually download the file via link https://get.helm.sh/helm-v3.8.2-linux-amd64.tar.gz, and remote copy to cka001.

scp -i cka-key-pair.pem ./Package/helm-v3.8.2-linux-amd64.tar.gz root@cka001:/root/

ssh -i cka-key-pair.pem root@cka001
tar -zxvf helm-v3.8.2-linux-amd64.tar.gz
cp linux-amd64/helm /usr/bin/
rm -rf linux-amd64 helm-v3.8.2-linux-amd64.tar.gz

Usage of Helm ¶

Check helm version

helm version

version.BuildInfo{Version:"v3.8.2", GitCommit:"6e3701edea09e5d55a8ca2aae03a68917630e91b", GitTreeState:"clean", GoVersion:"go1.17.5"}

Get help of helm.

helm help

Configure auto-completion for helm.

echo "source <(helm completion bash)" >> ~/.bashrc
source <(helm completion bash)

Install MySQL from Helm ¶

Add bitnami Chartes Repository.

helm repo add bitnami https://charts.bitnami.com/bitnami

Get current Charts repositories.

helm repo list

NAME    URL
bitnami https://charts.bitnami.com/bitnami

Sync up local Charts repositories.

helm repo update

Search bitnami Charts in repositories.

helm search repo bitnami

Search bitnami/mysql Charts in repositories.

helm search repo bitnami/mysql

Install MySQL Chart on namespace dev：

helm install mysql bitnami/mysql -n dev

Output

NAME: mysql
LAST DEPLOYED: Sun Jul 24 19:37:20 2022
NAMESPACE: dev
STATUS: deployed
REVISION: 1
TEST SUITE: None
NOTES:
CHART NAME: mysql
CHART VERSION: 9.2.1
APP VERSION: 8.0.29

** Please be patient while the chart is being deployed **

Tip:

  Watch the deployment status using the command: kubectl get pods -w --namespace dev

Services:

  echo Primary: mysql.dev.svc.cluster.local:3306

Execute the following to get the administrator credentials:

  echo Username: root
  MYSQL_ROOT_PASSWORD=$(kubectl get secret --namespace dev mysql -o jsonpath="{.data.mysql-root-password}" | base64 -d)

To connect to your database:

  1. Run a pod that you can use as a client:

      kubectl run mysql-client --rm --tty -i --restart='Never' --image  docker.io/bitnami/mysql:8.0.29-debian-11-r9 --namespace dev --env MYSQL_ROOT_PASSWORD=$MYSQL_ROOT_PASSWORD --command -- bash

  2. To connect to primary service (read/write):

      mysql -h mysql.dev.svc.cluster.local -uroot -p"$MYSQL_ROOT_PASSWORD"

Check installed release：

helm list

Result

NAME    NAMESPACE       REVISION        UPDATED                                 STATUS          CHART           APP VERSION
mysql   dev             1               2022-07-24 19:37:20.710988009 +0800 CST deployed        mysql-9.2.1     8.0.29

Check installed mysql release information.

helm status mysql

Check mysql Pod status.

kubectl get pod

Result

NAME                                      READY   STATUS    RESTARTS   AGE
mysql-0                                   1/1     Running   0          72s

Develop a Chart ¶

Below is a demo on how to develop a Chart.

Execute helm create to initiate a Chart：

# Naming conventions of Chart: lowercase a~z and -(minus sign)
helm create cka-demo

A folder cka-demo was created. Check the folder structure.

tree cka-demo/

Output

cka-demo/
├── charts
├── Chart.yaml
├── templates
│   ├── deployment.yaml
│   ├── _helpers.tpl
│   ├── hpa.yaml
│   ├── ingress.yaml
│   ├── NOTES.txt
│   ├── serviceaccount.yaml
│   ├── service.yaml
│   └── tests
│       └── test-connection.yaml
└── values.yaml

Delete or empty some files, which will be re-created later.

cd cka-demo
rm -rf charts
rm -rf templates/tests 
rm -rf templates/*.yaml
echo "" > values.yaml
echo "" > templates/NOTES.txt
echo "" > templates/_helpers.tpl
cd ..

Now new structure looks like below.

tree cka-demo/

Output

cka-demo/
├── Chart.yaml
├── templates
│   ├── _helpers.tpl
│   └── NOTES.txt
└── values.yaml

NOTES.txt ¶

NOTES.txt is used to provide summary information to Chart users. In the demo, we will use NOTES.txt to privide summary info about whether the user passed CKA certificate or not.

cd cka-demo/
vi templates/NOTES.txt

Add below info.

{{- if .Values.passExam }}
Congratulations!

You have successfully completed Certified Kubernetes Administrator China Exam (CKA-CN). 

Your CKA score is: {{ .Values.ckaScore }}

Click the link below to view and download your certificate.

https://trainingportal.linuxfoundation.org/learn/dashboard
{{- else }}
Come on! you can do it next time!
{{- end }}

Deployment Template ¶

Let's use Busybox service to generate information. We use kubectl create deployment --dry-run=client -oyaml to generate Deployment yaml file and write it the yaml file content into file templates/deployment.yaml.

kubectl create deployment cka-demo-busybox --image=busybox:latest --dry-run=client -oyaml > templates/deployment.yaml

Check content of deployment yaml file templates/deployment.yaml.

cat templates/deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    app: cka-demo-busybox
  name: cka-demo-busybox
spec:
  replicas: 1
  selector:
    matchLabels:
      app: cka-demo-busybox
  strategy: {}
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: cka-demo-busybox
    spec:
      containers:
      - image: busybox:latest
        name: busybox
        resources: {}
status: {}

Edit file templates/deployment.yaml.

vi templates/deployment.yaml

Let's replace value of .spec.replicas from 1 to a variable {{ .Values.replicaCount }}, so we can dynamicly assign replicas number for other Deployment.

apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    app: cka-demo-busybox
  name: cka-demo-busybox
spec:
  replicas: {{ .Values.replicaCount }}
  selector:
    matchLabels:
      app: cka-demo-busybox
  strategy: {}
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: cka-demo-busybox
    spec:
      containers:
      - image: busybox:latest
        name: busybox
        resources: {}
status: {}

The .spec.replicas will be replaced by actula value of .Values.replicaCount during deployment.

Let's create another file values.yaml and add a variable replicaCount with default value 1 into the file. Strong recommended to add comments for each value we defined in file values.yaml.

vi values.yaml

# Number of deployment replicas
replicaCount: 1

Let's add more variables into file templates/deployment.yaml.

Replace Release name .metadata.name by {{ .Release.Name }} and filled with variable defined in file values.yaml.
Replace label name .metadata.labels by {{- include "cka-demo.labels" . | nindent 4 }}, and filled with labels name cka-demo.labels defined in file _helpers.tpl.
Replace .spec.replicas by {{ .Values.replicaCount }} and filled with variable defined in file values.yaml.
Replace .spec.selector.matchLabels by {{- include "cka-demo.selectorLabels" . | nindent 6 }} and filled with cka-demo.selectorLabels defined in file _helpers.tpl.
Replace .spec.template.metadata.labels by {{- include "cka-demo.selectorLabels" . | nindent 8 }} and filled with cka-demo.selectorLabels defined in file _helpers.tpl.
Replace .spec.template.spec.containers[0].image by {{ .Values.image.repository }} and {{ .Values.image.tag }} and filled with variables defined in values.yaml for image name and image tag.
Replace .spec.template.spec.containers[0].command and add if-else statement, if .Values.passExam is true, execute commands defined in .Values.passCommand, if false, execute commands defined in .Values.lostCommand.
Use key from ConfigMap from .spec.template.spec.containers[0].env as prefix of ConfigMap name and filled with {{ .Values.studentName }} defined in file values.yaml.
Replace .spec.template.spec.containers[0].resources by {{ .Values.resources }} and filled with variable defined in file values.yaml.

The .Release.Name is built-in object, no need to be specified in file values.yaml. It's generated by Release by helm install.

Remove unused lines and final one looks like below.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ .Release.Name }}
  labels:
    {{- include "cka-demo.labels" . | nindent 4 }}
spec:
  replicas: {{ .Values.replicaCount }}
  selector:
    matchLabels:
      {{- include "cka-demo.selectorLabels" . | nindent 6 }}
  template:
    metadata:
      labels:
        {{- include "cka-demo.selectorLabels" . | nindent 8 }}
    spec:
      containers:
      - name: id-generator
        image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"
        {{- if .Values.passExam }}
        {{- with .Values.passCommand }}
        command: {{ range . }}
          - {{ . | quote }}
          {{- end }}
          {{- end }}
        {{- else }}
        {{- with .Values.lostCommand }}
        command: {{ range . }}
          - {{ . | quote }}
          {{- end }}
          {{- end }}
        {{- end }}
        env:
        - name: CKA_SCORE
          valueFrom:
            configMapKeyRef:
              name: {{ .Values.studentName }}-cka-score
              key: cka_score
        {{- with .Values.resources }}
        resources:
            {{- toYaml . | nindent 12 }}
          {{- end}}
      restartPolicy: Always

Update file values.yaml with variables default values. Suggestions：add variables one and test one, don't add all at one time.

vi values.yaml

# Number of deployment replicas 
replicaCount: 1

# Image repository and tag
image:
  repository: busybox
  tag: latest

# Container start command
passCommand:
  - '/bin/sh'
  - '-c'
  - "echo Your CKA score is $(CKA_SCORE) and your CKA certificate ID number is $(tr -dc 'A-Za-z0-9' < /dev/urandom | head -c 13; echo) ; sleep 86400"
lostCommand:
  - '/bin/sh'
  - '-c'
  - "echo Your CKA score is $(CKA_SCORE), Come on! you can do it next time! ; sleep 86400"

# Container resources
resources:
  limits:
    cpu: 200m
    memory: 256Mi
  requests:
    cpu: 100m
    memory: 128Mi

# Student Name
studentName: whoareyou

# Student pass CKA exam or not
passExam: true

ConfigMap Template ¶

ConfigMap is referred in the Deployment, hence we need define the ConfigMap template. We will combine name of ConfigMap and cka_score as a variable, like name-cka-score.

vi templates/configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Values.studentName }}-cka-score
  labels:
    {{- include "cka-demo.labels" . | nindent 4 }}
data:
  cka_score: {{ .Values.ckaScore | quote }}

The studentName was already defined in file values.yaml, we just need add ckaScore with default value.

vi values.yaml

# Student CKA Score
ckaScore: 100

_helpers.tpl ¶

Define a common template _helpers.tpl to add labels and labels of Selector for labels of Deployment and ConfigMap.

vi templates/_helpers.tpl

{{/*
Common labels
*/}}
{{- define "cka-demo.labels" -}}
{{ include "cka-demo.selectorLabels" . }}
{{- if .Chart.AppVersion }}
app.kubernetes.io/version: {{ .Chart.AppVersion | quote }}
{{- end }}
app.kubernetes.io/managed-by: {{ .Release.Service }}
{{- end -}}


{{/*
Selector labels
*/}}
{{- define "cka-demo.selectorLabels" -}}
app: {{ .Chart.Name }}
release: {{ .Release.Name }}
{{- end -}}

Chart.yaml ¶

We use CKA logo as the icon of Chart

wget https://www.cncf.io/wp-content/uploads/2021/09/kubernetes-cka-color.svg

Edit Chart.yaml file.

vi Chart.yaml

Append icon info in the file.

icon: file://./kubernetes-cka-color.svg

Add author info for the Chart

vi Chart.yaml

maintainers:
  - name: James.H

Final Chart.yaml looks like below. Don't forget to update appVersion: "v1.23" to current Kubernetes API version.

apiVersion: v2
name: cka-demo
description: A Helm chart for CKA demo.
type: application
version: 0.1.0
appVersion: "v1.23"
maintainers:
  - name: James.H
icon: file://./kubernetes-cka-color.svg

Chart Debug ¶

Use helm lint to verify above change.

helm lint

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

helm lint only check format of Chart, won't check Manifest file.

We can use helm install --debug --dry-run or helm template to check Manifest output in order to verify all yaml files are correct or not.

helm template cka-demo ./

Use helm install --debug --dry-run to simulate the installation. We can get expected results from two different options (passed or failed the CKA certificate).

helm install --debug --dry-run cka-demo ./ --create-namespace \
  -n cka \
  --set studentName=kubernetes \
  --set ckaScore=99 \
  --set passExam=true

helm install --debug --dry-run cka-demo ./ --create-namespace \
  -n cka \
  --set studentName=kubernetes \
  --set ckaScore=0 \
  --set passExam=false

Package Chart to .tgz file, and upload to repository, e.g., Chart Museum or OCI Repo.

cd ../
helm package cka-demo

Successfully packaged chart and saved it to: /root/cka-demo-0.1.0.tgz

Till now, we have done our task to develop a Chart. Let's install the Chart.

helm install cka-demo cka-demo-0.1.0.tgz --create-namespace \
  -n cka \
  --set studentName=kubernetes \
  --set ckaScore=0 \
  --set passExam=false

Result

NAME: cka-demo
LAST DEPLOYED: Sun Jul 24 19:58:36 2022
NAMESPACE: cka
STATUS: deployed
REVISION: 1
TEST SUITE: None
NOTES:
Come on! you can do it next time!

Check the deployment

helm list --all-namespaces

Result

NAME            NAMESPACE       REVISION        UPDATED                                 STATUS          CHART           APP VERSION
cka-demo        cka             1               2022-07-24 19:58:36.272093383 +0800 CST deployed        cka-demo-0.1.0  v1.23      
mysql           dev             1               2022-07-24 19:37:20.710988009 +0800 CST deployed        mysql-9.2.1     8.0.29

If any error, need to unstall cka-demo and reinstall it.

helm uninstall cka-demo -n <your_namespace>

Check log of cka-demo.

kubectl logs -n cka -l app=cka-demo

Result

Your CKA score is 0, Come on! you can do it next time!

Install cka-demo with different options.

helm uninstall cka-demo -n cka

helm install cka-demo cka-demo-0.1.0.tgz --create-namespace \
  -n cka \
  --set studentName=kubernetes \
  --set ckaScore=100 \
  --set passExam=true

NAME: cka-demo
LAST DEPLOYED: Sun Jul 24 20:01:34 2022
NAMESPACE: cka
STATUS: deployed
REVISION: 1
TEST SUITE: None
NOTES:
Congratulations!

You have successfully completed Certified Kubernetes Administrator China Exam (CKA-CN).

Your CKA score is: 100

Click the link below to view and download your certificate.

https://trainingportal.linuxfoundation.org/learn/dashboard

Check log of cka-demo.

kubectl logs -n cka -l app=cka-demo

Your CKA score is 100 and your CKA certificate ID number is BQKoVYVhjzl3G

Built-in Objects:

Release.Name                              # 发布名称
Release.Namespace                         # 发布Namespace
Release.Service                           # 渲染模板的服务，在Helm中默认值为"Helm"
Release.IsUpgrade                         # 如果当前是升级或回滚，设置为true
Release.IsInstall                         # 如果当前是安装，设置为true
Release.Revision                          # 发布版本号
Values                                    # 从values.yaml和--set传入，默认为空
Chart                                     # 所有Chart.yaml中的内容
Chart.Version                             #
Chart.Maintainers                         #
Files                                     # 在chart中访问非特殊文件
Capabilities                              # 提供关于支持能力的信息（K8s API版本、K8s版本、Helm版本）
Capabilities.KubeVersion                  # Kubernetes的版本号
Capabilities.APIVersions.Has "batch/v1"   # K8s API版本包含"batch/v1"
Template                                  # 当前模板信息
Template.Name                             # 当前模板文件路径
Template.BasePath                         # 当前模板目录路径

Reference: