Helm

1. What is Helm?

2. Components

3. Basics

4. Helm Charts

What is Helm?

• can be considered as package manager/automation tool for Kubernetes

• treat Kubernetes objects as an app, as part of a package as a group

• instead of modifying objects, only need to tell Helm what package to be modified

• knows which objects to change based on the package name

• no need to manage each Kubernetes object

• can install, upgrade, rollback or uninstall with only single command

• can specify desired values for the package at install time by only editing single file

• can be downloaded from [official Helm site](https://helm.sh/docs/intro/install/)

Helm 2 vs 3

• extra component, Tiller, has to be installed in the cluster for Helm 2 to communicate

Kubernetes did not have RBAC and CRD at that time * as Tiller is run in god mode, there are security concerns for the cluster * Tiller is not required anymore after RBAC and CRD * Helm 3 is simpler and better designed * 3-Way Strategic Merge Patch

• Helm 2 does not create new revision when objects are manually changed from kubectl,

so rollback is not possible after manual change - Helm 3 compares current chart, previous chart and live state, 3-way, for rollbacks

back to top

Components

Charts

• collection of files that contain instructions to create Kubernetes objects

• used to install applications into the cluster

• different charts can be found in public repository like docker images, called

[Helm Hub or Artifact Hub](https://artifacthub.io/) * values.yaml: store configurable values for the chart * chart.yaml

• store information about the chart, such as chart API Version, app version, name

• apiVersion field is added in Helm 3 to differentiate charts built in the past

• additional fields in Helm 2 will be ignored and can result in unexpected behavior

• every chart must have its own version, not same as appVersion field

• type: application is used for deploying applications

• type: library is a chart that provides utilities that help building charts

• Chart Directories

  • templates: templates directory

  • values.yaml: configurable values

  • chart.yaml: chart info

  • license: chart license

  • readme: readme file

  • charts: dependency charts

Release

• single installation of app, created when a chart is installed

• each release can have multiple revisions, snapshots of the app

• every change create a new revision

• can install multiple releases based on same chart

Metadata

• data such as installed release, charts used and revision state

• saved in the cluster as secrets

back to top

Basics

• helm search hub SEARCH_WORD: search chart in the hub or repositories

• helm repo add REPO_NAME REPO_URL: add repository before installation

• helm install NAME CHART_NAME: install chart to cluster

• helm list: list all releases

• helm uninstall NAME: uninstall and delete all objects

• heml repo SUB_COMMAND: interact with repositories

Chart Customization

• charts are installed with default values

• can change values from command line with --set flags

  • helm install --set PARAM_1="VALUE_1" --set PARAM_2="VALUE_2" NAME CHART_NAME

• create new custom-values.yaml and use it to override default values

  • helm install --values custom-values.yaml NAME CHART_NAME

• pull the chart first and edit values.yaml file

  • helm pull CHART_NAME or helm pull --untar CHART_NAME

  • helm install NAME LOCAL_CHART_DIR

Lifecycle Management

• helm keep track of releases with revision numbers

• helm upgrade NAME CHART_NAME: upgrade app, will create a new revision

• helm history NAME: list releases/lifecycle of an app with details

• helm rollback NAME REVISION_NUMBER: rollback to specific revision, create new revision

with similar configuration as given revision * some charts require administrative access for upgrade * rollbacks do not recover data * chart hooks are required to backup and restore data, especially in databases

back to top

Helm Charts

• versatile and can automate any kind of Kubernetes package installation

• similar to installation wizards on Operating Systems

• can write a chart to do operations any time upgrade/rollback is performed

• helm create NAME: create skeleton chart directory structure

• use Go templating language for dynamic chart values, such as {{ .Release.Name }}-myapp

• available objects for template directive: Release, Chart, Capabilities, Values

Verifying Charts

• Lint

  • validate YAML format

  • helm lint LOCAL_CHART_DIR

• Template

  • validate templating

  • helm template LOCAL_CHART_DIR or helm template NAME LOCAL_CHART_DIR

  • use with --debug to display error in generated YAML file

• Dry Run

  • validate chart works with the cluster

  • helm install NAME CHART_NAME --dry-run

Functions

• transform data from one format to another, {{ FUNCTION ARGUMENT }}

• {{ upper .Values.image.repository }}: convert to upprecase

• {{ quote .Values.image.repository }}: add quotes around the text

• {{ replace "x" "y" .Values.image.repository }}: function with three arguments, replace

‘x’ in the text with ‘y’ * {{ default "myimage" .Values.image.repository }}: default value to be used if not provided in the values.yml file * arguments not in quote are considered as variables * check [official docs](https://helm.sh/docs/chart_template_guide/function_list/) for more functions

back to top