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What is Helm ?

Oct 06, 2024, 7 min read

Installation

Official Homepage: https://helm.sh/

Info

What is Helm ?

Helm helps you manage Kubernetes applications — Helm Charts help you define, install, and upgrade even the most complex Kubernetes application.

Charts are easy to create, version, share, and publish — so start using Helm and stop the copy-and-paste.

Helm is a graduated project in the CNCF and is maintained by the Helm community.

Helm already installing and using on CI/CD, If you want to learn and work with Helm, feel free to installing on Installing Guide

Helm Template

All of application will base on template for releasing, you can understanding the concept with helm template

mychart
|-- Chart.yaml
|-- charts
|-- templates
|   |-- NOTES.txt
|   |-- _helpers.tpl
|   |-- deployment.yaml
|   |-- ingress.yaml
|   `-- service.yaml
`-- values.yaml

Question

Why we need the helm template ?

  • Make everything become simple for managing and replacing
  • Changing only one place and anything will come update for each environment (Consider when you want to change, make sure anything is working)
  • Flexible variables base on environment with values.yaml file

Related articles:

Priority of Value in Helm

Tip

To override values in a chart

  • use either the --values flag and pass in a file or use the --set flag and pass configuration from the command line
  • To force string values, use --set-string.
  • You can use --set-file to set individual values from a file when the value itself is too long for the command line or is dynamically generated.
  • You can also use --set-json to set json values (scalars/objects/arrays) from the command line.

You can specify the --values'/'-f flag multiple times. The priority will be given to the last (right-most) file specified.

You can specify the --set flag multiple times. The priority will be given to the last (right-most) set specified.

You can update the values for an existing release with this command as well via the --reuse-values flag. The RELEASE and CHART arguments should be set to the original parameters, and existing values will be merged with any values set via --values'/'-f or --set flags.

Related articles

Command usage

Helm will submit the role for both of CI and CD progress*

CI (Continuous Integration)

helm dependency

Documentation: doc

Purpose: manage a chart’s dependencies

Info

Manage the dependencies of a chart.

Helm charts store their dependencies in ‘charts/‘. For chart developers, it is often easier to manage dependencies in ‘Chart.yaml’ which declares all dependencies.

The dependency commands operate on that file, making it easy to synchronize between the desired dependencies and the actual dependencies stored in the ‘charts/’ directory.

Just use update optional for update charts/ based on the contents of Chart.yaml

Example:

Documentation: The Chart.yaml File

./deploy/xxxxx/xxxx/Chart.yaml
apiVersion: v2
name: xxxx
description: A Helm chart for Kubernetes
 
# A chart can be either an 'application' or a 'library' chart.
#
# Application charts are a collection of templates that can be packaged into versioned archives
# to be deployed.
#
# Library charts provide useful utilities or functions for the chart developer. They're included as
# a dependency of application charts to inject those utilities and functions into the rendering
# pipeline. Library charts do not define any templates and therefore cannot be deployed.
type: application
 
# This is the chart version. This version number should be incremented each time you make changes
# to the chart and its templates, including the app version.
# Versions are expected to follow Semantic Versioning (https://semver.org/)
version: 0.1.0
 
# This is the version number of the application being deployed. This version number should be
# incremented each time you make changes to the application. Versions are not expected to
# follow Semantic Versioning. They should reflect the version the application is using.
appVersion: 1.16.0
 
dependencies:
- name: common
  version: 0.1.0
  repository: "file://../../library/common/"

If you can see with Chart.yaml, you could understand what meaning of Chart with important value like

  • apiVersion : The chart API version (required) - Default to use helm3 with api v2 to applied deployment
  • name: The name of the chart (required) - This one will be effect to your kubernetes service, if name xxxx, for example your deployment name will be xxxx
  • dependencies: A list of the chart requirements (optional) - Take the common with pre-define for mapping change deployments and YAML manifests for application.

NOTICE: Application will use file with relative path, make sure ../../library/common/ exist

On CI progress, pipeline will trigger the action

helm dependency update ../xxxxx/charts/xxxx/

Success

With this action, your new chart application will create and publish artifact with

  • New value file if you change environment value
  • New variable of secret configmap, if you update them
  • Add new configuration like applying HPA to your application, for example

CD (Continuous Delivery)

helm update

Documentation: doc

Purpose: upgrade a release

Info

This command upgrades a release to a new version of a chart.

The upgrade arguments must be a release and chart. The chart argument can be either: a chart reference(‘example/mariadb’), a path to a chart directory, a packaged chart, or a fully qualified URL. For chart references, the latest version will be specified unless the --version flag is set.

Apply --install for purpose running both update and install if not exist Chart on Cluster

Question

You need to understand concept of value-file work with helm update to make sure not mistake occur when defining. NOTICE: The value will be set base on priority. Read Priority of Value in Helm to explain more

  1. All environment with sensitive need to be masking like connection strings, password database, secret key, … by force to using --set flag to set this part on the pipeline.
  2. Base on environment, you need to upgrading the specify value for each them like production-values.yaml uat-values.yaml systemtest-values.yaml
  3. If you do not set any value, default values.yaml is specify for general value

On CD progress, pipeline will trigger the action

helm upgrade --install xxxx -f ../xxxxx/environments/systemtest-values.yaml  --set mongodb.password=$(MONGODB_PWD) ../xxxxx/charts/xxxx

Success

With this action, If not wrong anything, your new application will release to K8s Cluster

Another command

helm install

To install helm chart from self-define or community from ArtifactHub

helm install <name-release> <chart-url>

helm list

To list releases on namespace 
helm list -n <namespace>

helm repo

To add, list, remove, update, and index chart repositories 
# Add a chart repository
helm repo add [NAME] [URL] [flags]
 
# Update information of available charts locally from chart repositories
helm repo update [REPO1 [REPO2 ...]] [flags]

helm uninstall

To uninstall a release

helm uninstall RELEASE_NAME [...] [flags]

Debug Template

Documentation: Doc

Info

Debugging templates can be tricky because the rendered templates are sent to the Kubernetes API server, which may reject the YAML files for reasons other than formatting.

There are a few commands that can help you debug.

  • helm lint is your go-to tool for verifying that your chart follows best practices
  • helm template --debug will test rendering chart templates locally.
  • helm install --dry-run --debug will also render your chart locally without installing it, but will also check if conflicting resources are already running on the cluster. Setting —dry-run=server will additionally execute any lookup in your chart towards the server.
  • helm get manifest: This is a good way to see what templates are installed on the server.

Conclusion

Success

On this topic, you will learn and understand about helm for

  • Install Helm for your environment, for debug or release
  • Understand priority value of helm chart
  • How to use command with helm ?
  • Tools for helping you debug the template before apply for real environment

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