theJaxon / helm-skillcred-SC104

Preparing for Developing Helm Charts (SC104) - a credential by LinuxFoundation

helm-skillcred-SC104

Preparing for Developing Helm Charts (SC104) - a credential by LinuxFoundation

Basic commands

Getting release info

helm get all

helm get manifest

helm get notes

helm get values

# Get all values used by a release (Including defaults)
helm get values --all

helm get hooks

Getting chart related info

helm show all # Show all chart information

helm show chart # Display Chart definition

helm show readme 

helm show values

---

Create charts using basic templating

helm create <chart-name>

Chart dependencies

In the dependencies map in Chart.yaml many fields are supported

• The mandatory ones are name, repository and version
• condition: Boolean value that determines whether the dependency should be included or not
• Tags: A list of Boolean values that determine whether the chart should be included or not
• import-values: Mapping of source values to parent values
• Alias: alternative name given to the dependency (Used when working with multiple versions of same dependency)

# Conditionally install redis dependency
dependencies:
  - name: redis
    repository: https://charts.bitnami.com/bitnami
    version: 18.0.0
    condition: redis.enabled

# By default if not specified in values, the condition will be ignored meaning dependency will be installed anyway unless explicitly specified as false
helm install . --generate-name # redis dependency is included 

# Here redis dependency won't be installed
helm upgrade <release-name> <chart-location> --set redis.enabled=false

dependencies:
  - name: mariadb
    repository: https://charts.bitnami.com/bitnami
    version: 13.1.1
    tags:
      - backend
      - database
  - name: redis
    repository: https://charts.bitnami.com/bitnami
    version: 18.0.0
    tags:
      - backend
      - cache

# Both dependencies will be installed
helm upgrade --install jaxon .

# backend tag is disabled so that all dependencies aren't installed
# Then only redis is picked for installation by enabling the cache tag
helm upgrade --install jaxon . --set tags.backend=false --set tags.cache=true

• Both conditions and tags can be combined, however conditions always overrides tags

---

Basic Templating

Objects

1. Release object

• Used to get helm release metadata
• .Release.Name and .Release.Namespace are commonly used
• .Release.IsUpgrade and .Release.IsInstall The first boolean is for whehter there's an upgrade or rollback, the second one is for installation

Control Structure

If/Else

• Conditional blocks for resource creation

{{- if .Values.configmap.enabled  }}
data:
{{- $configmap := printf "configs/%s/%s/config.yaml" .Values.name .Release.Namespace }}
{{ (.Files.Glob $configmap ).AsConfig | indent 2 }}
{{- end }}

with

• Modifies the scope of the resources being generated

{{- with .Values.jaxon }}
  username: {{ .username }}
  password: {{ .password }}
{{- end }}

range

• Used for iterating over list of items and also changes the scope just like with

rhel:
  - name: RHCSA
    exam: EX200
  - name: RHCE
    exam: EX294

{{- range .Values.rhel }}
name: {{ .name }}
exam: {{ .exam }}
{{- end }}

---

Use chart hooks

• Allow chart developers to intervene at certain points in a release's life cycle
• For each of (install, delete, upgrade and rollback) there's pre and post hook
• There's also a test hook that executes when helm test command is invoked
• helm.sh/weight annotation can be used when a specific hook type exists multiple times and we need to prioritize one over the other
• Multiple hooks can be specified using a comma separated list helm.sh/hook: pre-rollback,post-rollback

---

Testing helm charts

Templating and validating

• Charts can be tested with client-side rendering via helm template command
• In order to have server side validation one can add --validate to the above command or can try running helm install --dry-run

Testing on a live kubernetes cluster

Can be broken into 2 ways

1. Readiness probes with helm install --wait which makes return success status only once readiness probe passes
2. Test hooks and helm test command (Test hooks are just pods that do some specific task after helm install is executed)

• You specify that it's a test hook via helm.sh/hook: test annotation