Helm Package Manager

Reference: helm.sh, Google Cloud Training - Helm Package Manager, bmc blogs - Introduction to Kubernetes Helm Charts

What is Helm?

• Kubernetes package manager이다

  • K8s equivalent of yum , apt, or npm!

• Helm은 charts라는 packaging format을 사용한다

  • 여기서 chart는 k8s resources를 describe하는 file들의 집합이다

  • chart는 무언가를 배포하기 위해 사용된다

    • ex) memcached pod, web app w/ HTTP servers, databases, etc.

  • chart는 특정 directory tree로 구성된 file들로 생성되어 있다

    • 이 file들은 배포될 version의 archive로 packaging 될 수 있다

The Chart File Structure

• Chart는 directory 내부에 일련의 파일들로 구성되어 있다

• Directory의 이름 == chart 이름 (versioning 정보를 제외한)이다

  • ex) WordPress를 describe 하는 chart는 wordpress/에 저장된다

• Directory 내부에, Helm은 아래의 구조를 필요로 한다

  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

  • Helm은 charts/, crds/, templates/ directory와 위의 예시에 나와있는 모든 파일들의 이름을 예약하여 사용한다

The Chart.yaml File

Chart.yaml file은 chart의 필수 구성 요소이며, 아래의 fields를 포함하고 있다

apiVersion: The chart API version (required)
name: The name of the chart (required)
version: A SemVer 2 version (required)
kubeVersion: A SemVer range of compatible Kubernetes versions (optional)
description: A single-sentence description of this project (optional)
type: The type of the chart (optional)
keywords:
  - A list of keywords about this project (optional)
home: The URL of this projects home page (optional)
sources:
  - A list of URLs to source code for this project (optional)
dependencies: # A list of the chart requirements (optional)
  - name: The name of the chart (nginx)
    version: The version of the chart ("1.2.3")
    repository: (optional) The repository URL ("https://example.com/charts") or alias ("@repo-name")
    condition: (optional) A yaml path that resolves to a boolean, used for enabling/disabling charts (e.g. subchart1.enabled )
    tags: # (optional)
      - Tags can be used to group charts for enabling/disabling together
    import-values: # (optional)
      - ImportValues holds the mapping of source values to parent key to be imported. Each item can be a string or pair of child/parent sublist items.
    alias: (optional) Alias to be used for the chart. Useful when you have to add the same chart multiple times
maintainers: # (optional)
  - name: The maintainers name (required for each maintainer)
    email: The maintainers email (optional for each maintainer)
    url: A URL for the maintainer (optional for each maintainer)
icon: A URL to an SVG or PNG image to be used as an icon (optional).
appVersion: The version of the app that this contains (optional). Needn't be SemVer. Quotes recommended.
deprecated: Whether this chart is deprecated (optional, boolean)
annotations:
  example: A list of annotations keyed by name (optional).

위에 명시되어 있지 않은 다른 fields는 적용되지 않는다