Helm

Helm is a tool for managing Charts. Charts are packages of pre-configured Kubernetes resources.

Use Helm to:

  • Find and use popular software packaged as Helm Charts to run in Kubernetes
  • Share your own applications as Helm Charts
  • Create reproducible builds of your Kubernetes applications
  • Intelligently manage your Kubernetes manifest files
  • Manage releases of Helm packages

Helm 是 Kubernetes 的一个包管理工具 (The Kubernetes Package Manager)，用来简化 Kubernetes 应用的部署和管理。可以把 Helm 比作 CentOS 的 yum 工具。 使用 Helm 可以完成以下事情：

  • 管理 Kubernetes manifest files
  • 管理 Helm 安装包 Charts
  • 基于 Chart 的 Kubernetes 应用分发

Helm in a Handbasket

Helm is a tool that streamlines installing and managing Kubernetes applications. Think of it like apt/yum/homebrew for Kubernetes.

  • Helm renders your templates and communicates with the Kubernetes API
  • Helm runs on your laptop, CI/CD, or wherever you want it to run.
  • Charts are Helm packages that contain at least two things:
    • A description of the package (Chart.yaml)
    • One or more templates, which contain Kubernetes manifest files
  • Charts can be stored on disk, or fetched from remote chart repositories (like Debian or RedHat packages)

Install

Binary downloads of the Helm client can be found on the Releases page.

Unpack the helm binary and add it to your PATH and you are good to go!

To rapidly get Helm up and running, start with the Quick Start Guide.

See the installation guide for more options, including installing pre-releases.

基本概念

  • Chart: 是 Helm 管理的安装包，里面包含需要部署的安装包资源。可以把 Chart 比作 CentOS yum 使用的 rpm 文件。每个 Chart 包含下面两部分：
    • 包的基本描述文件 Chart.yaml
    • 放在 templates 目录中的一个或多个 Kubernetes manifest 文件模板
  • Release: 是 Chart 的部署实例，一个 Chart 在一个 Kubernetes 集群上可以有多个 Release，即这个 Chart 可以被安装多次
  • Repository: Chart 的仓库，用于发布和存储 Chart

使用 helm create mychart 创建一个名为 mychart 的示例，再使用 tree mychart 命令看一下 chart 的目录结构。

mychart
├── Chart.yaml
├── charts                      # 该目录保存其他依赖的 chart（子 chart）
├── templates                   # chart 配置模板，用于渲染最终的 Kubernetes YAML 文件
│   ├── NOTES.txt               # 用户运行 helm install 时候的提示信息
│   ├── _helpers.tpl            # 用于创建模板时的帮助类
│   ├── deployment.yaml         # Kubernetes deployment 配置
│   ├── ingress.yaml            # Kubernetes ingress 配置
│   ├── service.yaml            # Kubernetes service 配置
│   ├── serviceaccount.yaml     # Kubernetes serviceaccount 配置
│   └── tests
│       └── test-connection.yaml
└── values.yaml                 # 定义 chart 模板中的自定义配置的默认值，可以在执行 helm install 或 helm update 的时候覆盖
  • Chart.yaml：用于描述这个 Chart 的基本信息，包括名字、描述信息以及版本等
  • values.yaml ：用于存储 templates 目录中模板文件中用到变量的值。
  • templates： 目录里面存放所有 yaml 模板文件。
  • charts：目录里存放这个 chart 依赖的所有子 chart。
  • NOTES.txt ：用于介绍 Chart 帮助信息， helm install 部署后展示给用户。例如：如何使用这个 Chart、列出缺省的设置等。
  • _helpers.tpl：放置模板助手的地方，可以在整个 chart 中重复使用

Quickstart Guide

This guide covers how you can quickly get started using Helm.

Prerequisites

The following prerequisites are required for a successful and properly secured use of Helm.

  1. A Kubernetes cluster
  2. Deciding what security configurations to apply to your installation, if any
  3. Installing and configuring Helm.

Install Kubernetes or have access to a cluster

  • You must have Kubernetes installed. For the latest release of Helm, we recommend the latest stable release of Kubernetes, which in most cases is the second-latest minor release.
  • You should also have a local configured copy of kubectl.

See the Helm Version Support Policy for the maximum version skew supported between Helm and Kubernetes.

Install Helm

Download a binary release of the Helm client. You can use tools like homebrew, or look at the official releases page.

For more details, or for other options, see the installation guide.

Initialize a Helm Chart Repository

Once you have Helm ready, you can add a chart repository. Check Artifact Hub for available Helm chart repositories.

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

Once this is installed, you will be able to list the charts you can install:

$ helm search repo bitnami
NAME                             	CHART VERSION	APP VERSION  	DESCRIPTION
bitnami/bitnami-common           	0.0.9        	0.0.9        	DEPRECATED Chart with custom templates used in ...
bitnami/airflow                  	8.0.2        	2.0.0        	Apache Airflow is a platform to programmaticall...
bitnami/apache                   	8.2.3        	2.4.46       	Chart for Apache HTTP Server
bitnami/aspnet-core              	1.2.3        	3.1.9        	ASP.NET Core is an open-source framework create...
# ... and many more

Install an Example Chart

To install a chart, you can run the helm install command. Helm has several ways to find and install a chart, but the easiest is to use the bitnami charts.

$ helm repo update              # Make sure we get the latest list of charts
$ helm install bitnami/mysql --generate-name
NAME: mysql-1612624192
LAST DEPLOYED: Sat Feb  6 16:09:56 2021
NAMESPACE: default
STATUS: deployed
REVISION: 1
TEST SUITE: None
NOTES: ...

In the example above, the bitnami/mysql chart was released, and the name of our new release is mysql-1612624192.

You get a simple idea of the features of this MySQL chart by running helm show chart bitnami/mysql. Or you could run helm show all bitnami/mysql to get all information about the chart.

Whenever you install a chart, a new release is created. So one chart can be installed multiple times into the same cluster. And each can be independently managed and upgraded.

The helm install command is a very powerful command with many capabilities. To learn more about it, check out the Using Helm Guide

Learn About Releases

It’s easy to see what has been released using Helm:

$ helm list
NAME            	NAMESPACE	REVISION	UPDATED                             	STATUS  	CHART      	APP VERSION
mysql-1612624192	default  	1       	2021-02-06 16:09:56.283059 +0100 CET	deployed	mysql-8.3.0	8.0.23

The helm list (or helm ls) function will show you a list of all deployed releases.

Uninstall a Release

To uninstall a release, use the helm uninstall command:

$ helm uninstall mysql-1612624192
release "mysql-1612624192" uninstalled

This will uninstall mysql-1612624192 from Kubernetes, which will remove all resources associated with the release as well as the release history.

If the flag --keep-history is provided, release history will be kept. You will be able to request information about that release:

$ helm status mysql-1612624192
Status: UNINSTALLED
...

Because Helm tracks your releases even after you’ve uninstalled them, you can audit a cluster’s history, and even undelete a release (with helm rollback).

Reading the Help Text

To learn more about the available Helm commands, use helm help or type a command followed by the -h flag:

$ helm get -h

Glossary

Chart

A Helm package that contains information sufficient for installing a set of Kubernetes resources into a Kubernetes cluster.

Charts contain a Chart.yaml file as well as templates, default values (values.yaml), and dependencies.

Charts are developed in a well-defined directory structure, and then packaged into an archive format called a chart archive.

Chart Archive

A chart archive is a tarred and gzipped (and optionally signed) chart.

Chart Dependency (Subcharts)

  • Soft dependency: A chart may simply not function without another chart being installed in a cluster. Helm does not provide tooling for this case. In this case, dependencies may be managed separately.

  • Hard dependency: A chart may contain (inside of its charts/ directory) another chart upon which it depends. In this case, installing the chart will install all of its dependencies. In this case, a chart and its dependencies are managed as a collection.

When a chart is packaged (via helm package) all of its hard dependencies are bundled with it.

Chart Version

Charts are versioned according to the SemVer 2 spec. A version number is required on every chart.

Chart.yaml

Information about a chart is stored in a special file called Chart.yaml. Every chart must have this file.

Helm (and helm)

Helm is the package manager for Kubernetes. As an operating system package manager makes it easy to install tools on an OS, Helm makes it easy to install applications and resources into Kubernetes clusters.

While Helm is the name of the project, the command line client is also named helm. By convention, when speaking of the project, Helm is capitalized. When speaking of the client, helm is in lowercase.

Release

When a chart is installed, the Helm library creates a release to track that installation.

A single chart may be installed many times into the same cluster, and create many different releases. For example, one can install three PostgreSQL databases by running helm install three times with a different release name.

Release Number (Release Version)

A single release can be updated multiple times. A sequential counter is used to track releases as they change. After a first helm install, a release will have release number 1. Each time a release is upgraded or rolled back, the release number will be incremented.

Repository (Repo, Chart Repository)

Helm charts may be stored on dedicated HTTP servers called chart repositories (repositories, or just repos).

A chart repository server is a simple HTTP server that can serve an index.yaml file that describes a batch of charts, and provides information on where each chart can be downloaded from. (Many chart repositories serve the charts as well as the index.yaml file.)

A Helm client can point to zero or more chart repositories. By default, Helm clients are not configured with any chart repositories. Chart repositories can be added at any time using the helm repo add command.

Values (Values Files, values.yaml)

Values provide a way to override template defaults with your own information.

Helm Charts are “parameterized”, which means the chart developer may expose configuration that can be overridden at installation time. For example, a chart may expose a username field that allows setting a user name for a service.

These exposed variables are called values in Helm parlance.

Values can be set during helm install and helm upgrade operations, either by passing them in directly, or by using a values.yaml file.

Docs

Get started with the Quick Start guide or plunge into the complete documentation

Refer