[Kubernetes]Understand how to use helm chart in Kubernetes

Purpose

To understand How to use helm chart in Kubernetes

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Helm chart directory structure

wordpress/
  Chart.yaml          # A YAML file containing information about the chart
  LICENSE             # OPTIONAL: A plain text file containing the license for the chart
  README.md           # OPTIONAL: A human-readable README file
  values.yaml         # The default configuration values for this chart
  values.schema.json  # OPTIONAL: A JSON Schema for imposing a structure on the values.yaml file
  charts/             # A directory containing any charts upon which this chart depends.
  crds/               # Custom Resource Definitions
  templates/          # A directory of templates that, when combined with values,
                      # will generate valid Kubernetes manifest files.
  templates/NOTES.txt # OPTIONAL: A plain text file containing short usage notes

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Find helm chart - helm search

helm search repo/hub [chartname]

필요한 helm chart가 있는 경우 해당 chart가 포함된 repo를 helm에 추가하고 사용할 수 있다.
e.g. prometheus를 kubernetes에 설치하고 싶은 경우 아래와 같이 repo를 먼저 추가한뒤 helm search 명령어로 필요한 chart를 다운 받아서 사용할 수 있다.

helm repo add prometheus-community https://prometheus-community.github.io/helm-charts

## helm repo에서 prometheus chart 찾기
helm search repo prometheus

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Download and install helm chart - helm fetch and install

Before install helm chart, you can change values.yaml file what you want

helm fetch [helmchart]
helm install [helmchart] .[chart-path] -n [namespace]
helm uninstall [helmchart] -n [namespace]

## example
helm fetch prometheus-community/prometheus
helm install my-prometheus -f ./values.yaml . -n monitoring
helm uninstall my-prometheus -n monitoring

Option

• template debug
  1. lint : verify template and dependencies
  2. --dry-run : you can see template yaml files and error

1. helm lint prometheus-operator
2. helm install prometheus-operator . --dry-run

 

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Helm upgrade - After edit value.yaml

helm upgrade -n prometheus prometheus -f ./values.yaml ./ 

helm history -n prometheus prometheus
REVISION        UPDATED                         STATUS          CHART                           APP VERSION     DESCRIPTION
1               Fri Apr  2 13:17:14 2021        superseded      prometheus-operator-9.3.2       0.38.1          Install complete
2               Fri Apr  2 13:24:14 2021        deployed        prometheus-operator-9.3.2       0.38.1          Upgrade complete

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Rollback helm chart

When you have some problem in your helm chart you can rollback your deploy

helm history [releasename]
helm rollback [releasename] [versionnumber-with-status-deployed]
helm rollback prometheus 5

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If you don't want to remove resource such as pvc

metadata:
  annotations:
    "helm.sh/resource-policy": keep
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