Helm

Introduction

• Helm is a package manager for Kubernetes that simplifies the deployment and management of applications on a Kubernetes cluster.

• It is organized as a collection of files inside of a directory. The directory name is the name of the chart (without versioning information). Thus, a chart describing WordPress would be stored in a wordpress/ directory.

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

Chart

Introduction

• A chart is a collection of files that describe a set of Kubernetes resources, such as deployments, services, config maps, and more. It provides a standardized and repeatable way to define, configure, and deploy complex applications on Kubernetes. So that, the resources can be deployed at once. It contains the following fields

Chart.yaml

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).

Repository & Dependencies

• A Repository is the place where charts can be collected and shared. It's like Perl's CPAN archive or the Fedora Package Database, but for Kubernetes packages.
• In Helm, one chart may depend on any number of other charts. These dependencies can be dynamically linked using the dependencies field in Chart.yaml or brought in to the charts/ directory and managed manually.

dependencies:
  - name: apache
    version: 1.2.3
    repository: https://example.com/charts
    condition: apache.enabled,global.apache.enabled
    tags:
      - apache
  - name: mysql
    version: 3.2.1
    repository: https://another.example.com/charts
  - name: abc
    alias: abc
    repository: file://./abc
    # specify correct version (find in file://./bot-builder-custom-helm-chart)
    version: 1.0.0-a

• After declaring the source of dependencies, it is needed to fetch the dependency charts

helm dependency update

When helm dependency update retrieves charts, it will store them as chart archives in the charts/ directory. So the charts will be fetched in format of zip file

charts/
  apache-1.2.3.tgz
  mysql-3.2.1.tgz

Templates & Values

Introduction

• Helm Chart templates are written in the Go template language
• All template files are stored in a chart's templates/ folder. When Helm renders the charts, it will pass every file in that directory through the template engine.

• Values (Variables) for the templates are supplied two ways:

  • Chart developers may supply a file called values.yaml inside of a chart. This file can contain default values.

  • Chart users may supply a YAML file that contains values. This can be provided on the command line with helm install

values.yaml

serviceAccount:
  # Specifies whether a service account should be created
  create: true
  # Automatically mount a ServiceAccount's API credentials?
  automount: true
  # Annotations to add to the service account
  annotations:
    eks.amazonaws.com/role-arn: arn:aws:iam::855441561601:role/eks-role-bot-builder-custom-helm-chart
  # The name of the service account to use.
  # If not set and create is true, a name is generated using the fullname template
  name: "bot-builder-custom-helm-chart"

serviceaccount.yaml

{{- if .Values.serviceAccount.create -}}
apiVersion: v1
kind: ServiceAccount
metadata:
  name: {{ include "bot-builder-custom-helm-chart.serviceAccountName" . }}
  labels:
    {{- include "bot-builder-custom-helm-chart.labels" . | nindent 4 }}
  {{- with .Values.serviceAccount.annotations }}
  annotations:
    {{- toYaml . | nindent 4 }}
  {{- end }}
automountServiceAccountToken: {{ .Values.serviceAccount.automount }}
{{- end }}

Override

• Parent Values file can supply values to the chart as well as to any of its dependencies

• E.g: Wordpress contains mysql chart and apache chart, the values can be declared in parent value file, it will override or supply the value to the child

• The value must be started with child alias as a prefix

title: "My WordPress Site" # Sent to the WordPress template

mysql:
  max_connections: 100 # Sent to MySQL
  password: "secret"

apache:
  port: 8080 # Passed to Apache

• Values are namespaced, but namespaces are pruned. So for the WordPress chart, it can access the MySQL password field as .Values.mysql.password. But for the MySQL chart, the scope of the values has been reduced and the namespace prefix removed, so it will see the password field simply as .Values.password.

Global

• Helm supports special "global" value. example:

title: "My WordPress Site" # Sent to the WordPress template

global:
  app: MyWordPress

mysql:
  max_connections: 100 # Sent to MySQL
  password: "secret"

apache:
  port: 8080 # Passed to Apache

• It will be regenerated the result like this

title: "My WordPress Site" # Sent to the WordPress template

global:
  app: MyWordPress

mysql:
  global:
    app: MyWordPress
  max_connections: 100 # Sent to MySQL
  password: "secret"

apache:
  global:
    app: MyWordPress
  port: 8080 # Passed to Apache

Pre-built Object

• Release: This object describes the release itself. It has several objects inside of it:

  • Release.Name: The release name

  • Release.Namespace: The namespace to be released into (if the manifest doesn’t override)

  • Release.IsUpgrade: This is set to true if the current operation is an upgrade or rollback.

  • Release.IsInstall: This is set to true if the current operation is an install.

  • Release.Revision: The revision number for this release. On install, this is 1, and it is incremented with each upgrade and rollback.

  • Release.Service: The service that is rendering the present template. On Helm, this is always Helm.

• Values: Values passed into the template from the values.yaml file and from user-supplied files. By default, Values is empty.

• Chart: The contents of the Chart.yaml file. Any data in Chart.yaml will be accessible here. For example {{ .Chart.Name }}-{{ .Chart.Version }} will print out the mychart-0.1.0.

  • The available fields are listed in the Charts Guide
• Files: This provides access to all non-special files in a chart. While you cannot use it to access templates, you can use it to access other files in the chart. See the section Accessing Files for more.

  • Files.Get is a function for getting a file by name (.Files.Get config.ini)

  • Files.GetBytes is a function for getting the contents of a file as an array of bytes instead of as a string. This is useful for things like images.

  • Files.Glob is a function that returns a list of files whose names match the given shell glob pattern.

  • Files.Lines is a function that reads a file line-by-line. This is useful for iterating over each line in a file.

  • Files.AsSecrets is a function that returns the file bodies as Base 64 encoded strings.

  • Files.AsConfig is a function that returns file bodies as a YAML map.

Release

Introduction

• A Release is an instance of a chart running in a Kubernetes cluster. One chart can often be installed many times into the same cluster. And each time it is installed, a new release is created. Consider a MySQL chart. If you want two databases running in your cluster, you can install that chart twice. Each one will have its own release, which will in turn have its own release name.

Command

• Here are the commands of manage release based on the chart

# Init
helm create <name>
# List
helm list --namespace <namespace> 
# Create helm release
helm install <release name>  -f <directory of value file> <chart folder name> --namespace <namespace>
# Update 
helm upgrade <release name> -f <directory of value file> <chart folder name> --namespace <namespace>
# Delete
helm uninstall <release name> --namespace <namespace>

Reference

Helm | Charts