Helm Subcharts - Dependency Command

Step-01: Introduction

• Create Parent Chart
• helm dependency list
• helm dependency update
• helm dependency build
• helm dependency version constraints
• helm dependency repository @REPO vs REPO-URL

Step-02: Create Parent Chart

# Create Parent Chart
helm create parentchart

Step-03: Update Helm Dependencies in Parent Chart Chart.yaml

apiVersion: v2
name: parentchart
description: A Helm chart for Kubernetes
type: application
version: 0.1.0
appVersion: "1.16.0"
dependencies:
  - name: mychart1
    version: "0.1.0"
    repository: "https://stacksimplify.github.io/helm-charts/"
  - name: mychart2
    version: "0.4.0"
    repository: "https://stacksimplify.github.io/helm-charts/"
  - name: mysql
    version: "9.9.0"
    repository: "https://charts.bitnami.com/bitnami"

Step-04: Helm Dependency Commands - List and Update

• helm dependency list: List all of the dependencies declared in a chart.
• helm dependency update: update parent chart charts/ folded based on the contents of file Chart.yaml

# Helm Dependency List
helm dependency list
Observation:
You should see status "missing" because we still didnt do helm dependency update

# Verify Charts folder in parentchart
ls parentchart/charts
Observation: it should be empty. Dependency subcharts not downloaded

# Helm Dependency Update
helm dependency update CHART-NAME
helm dependency update parentchart/
ls parentchart/charts
Observation:
1. We should see both charts (mychart1-0.1.0.tgz, mychart2-0.4.0.tgz, mysql-9.9.0.tgz)downloaded to "parentchart/charts" folder
2. We should see "Chart.lock" file in "parentchart" folder

# Review Chart.lock file
cat parentchart/Chart.lock

# Helm Dependency list
helm dependency list parentchart/
Observation: Should see status as "OK"

Step-05: Helm Dependency Chart Version Ranges

• Updates to parent chart Chart.yaml

Step-05-01: Helm Chart Version Notation

Helm Chart Version Notation: Major.Minor.Patch
MySQL Helm Chart Version: 9.10.8
Major: 9
Minor: 10
Patch: 8

Step-05-02: Basic Comparison Operators

• We can define the version constraints using basic comparison operators
• Where possible, use version ranges instead of pinning to an exact version.

# Basic Comparison Operators
version: "= 9.10.8"
version: "!= 9.10.8"
version: ">= 9.10.8"
version: "<= 9.10.8"
version: "> 9.10.8"
version: "< 9.10.8"
version: ">= 9.10.8 < 9.11.0"

Step-05-03: For Range Comparison Major: Caret Symbol(ˆ)

• x is a placeholder
• The caret (^) operator is for major level changes once a stable (1.0.0) release has occurred.

# For Range Comparison Major: Caret Symbol(ˆ)
^9.10.1  is equivalent to >= 9.10.1, < 10.0.0
^9.10.x  is equivalent to >= 9.10.0, < 10.0.0
^9.10    is equivalent to >= 9.10, < 10
^9.x     is equivalent to >= 9.0.0, < 10
^0       is equivalent to >= 0.0.0, < 1.0.0

Step-05-05: For Range Comparison Minor: Tilde Symbol(~)

• x is a placeholder
• The tilde (~) operator is for
  • patch level ranges when a minor version is specified
  • major level changes when the minor number is missing.
• The suggested default is to use a patch-level version match which is first one in the below table

# For Range Comparison Major: Caret Symbol(ˆ)
~9.10.1  is equivalent to >= 9.10.1, < 9.11.0 # Patch-level version match
~9.10    is equivalent to >= 9.10, < 9.11
~9       is equivalent to >= 9, < 10
^9.x     is equivalent to >= 9.0.0, < 10
^0       is equivalent to >= 0.0.0, < 1.0.0

Step-05-06: Verify with some examples

dependencies:
- name: mysql
  version:" "9.10.9"
  #version: ">=9.10.1" # Should dowload latest version available as on that day
  #version: "<=9.10.6" # Should download 9.10.6 mysql helm chart package
  #version: "~9.9.0" # Should download latest from 9.9.x (Patch version)
  #version: "~9.9" # Should download latest from 9.9
  #version: "~9" # Should download latest from 9.x
  repository: "https://charts.bitnami.com/bitnami"


# helm dependency update
helm dependency update
or
helm dep update

Step-06: Helm Dependency Build Command

• helm dependency build: rebuild the charts/ directory based on the Chart.lock file
• In short dep update command will negotiate with version constraints defined in Chart.yaml where as dep build will try to build or download or update whatever version preset in Chart.lock file
• If no lock file is found, helm dependency build will mirror the behavior of helm dependency update.

# helm dependency build
helm dependency build CHART-NAME
helm dependency build parentchart

Step-07: Helm Dependency Repository @REPO vs REPO-URL

• When we are using Helm with DevOps pipelines across environments "@REPO" approach is not recommended
• REPO-URL approach (repository: "https://charts.bitnami.com/bitnami") is always recommended

# With Repository URL (Recommended approach)
dependencies:
- name: mysql
  version: ">=9.10.8"
  repository: "https://charts.bitnami.com/bitnami"

# List Helm Repo
helm repo list
helm search repo bitnami/mysql --versions

# With @REPO (local repo reference - NOT RECOMMENDED)
dependencies:
- name: mysql
  version: ">=9.10.8"
  repository: "@bitnami"

# Clean-Up Charts folder and Chart.lock
rm parentchart/charts/*
rm parentchart/Chart.lock

# Ensure we are using repository: "@bitnami"
helm dependency update
ls parentchart/charts/
cat parentchart/Chart.lock
Observation: Should work as expected