Helm Charts Explained

What is Helm?

Helm is a package manager for Kubernetes. Just like apt manages packages on Debian or brew on macOS, Helm manages Kubernetes applications. It bundles multiple K8s manifests into a single deployable unit called a Chart.

Without Helm

deployment.yaml
service.yaml
configmap.yaml
ingress.yaml
secret.yaml
hpa.yaml
... manage each one separately

With Helm

helm install my-app ./chart

One command deploys everything

Three Core Concepts

Chart

A package of templated K8s manifests + metadata

Release

A specific instance of a chart deployed to a cluster

Repository

A place to store and share charts (like Docker Hub)

Chart Directory Structure

my-chart/

Chart.yaml required

Metadata: name, version, dependencies

values.yaml required

Default configuration values

charts/

Dependency charts (subcharts)

templates/

Go-templated K8s manifests

deployment.yaml

service.yaml

ingress.yaml

configmap.yaml

_helpers.tpl

Reusable template partials

NOTES.txt

Post-install usage notes

.helmignore

Files to exclude from packaging

Chart.yaml

apiVersion: v2
name: my-app
version: 1.2.0
appVersion: "3.1.0"
description: My app chart
dependencies:
  - name: postgresql
    version: "12.x"
    repository: "https://..."

values.yaml

replicaCount: 3
image:
  repository: myapp
  tag: "3.1.0"
service:
  type: ClusterIP
  port: 8080
ingress:
  enabled: true
  host: app.example.com

How Helm Renders & Deploys

Helm merges templates + values → renders plain YAML → applies to cluster

Templates

replicas: {{ .Values.replicaCount }}
image: {{ .Values.image.repo }}

Values

replicaCount: 3
image:
  repo: myapp:v2

Helm Template Engine

Go text/template + Sprig functions

Rendered Kubernetes YAML

apiVersion: apps/v1
kind: Deployment
spec:
  replicas: 3          # resolved!
  containers:
    - image: myapp:v2  # resolved!

Kubernetes Cluster

kubectl apply (under the hood)

Value Override Priority (lowest → highest)

1 values.yaml (defaults)

2 -f custom.yaml

3 --set key=val

4 --set-string key=val

Release Lifecycle

Helm tracks every change as a numbered revision, making rollbacks trivial.

Install helm install my-release ./chart

Deploy chart as a new release → Revision 1

Upgrade helm upgrade my-release ./chart

Apply changes → Revision N+1 (keeps history)

Rollback helm rollback my-release 1

Revert to any previous revision instantly

Uninstall helm uninstall my-release

Remove all resources of the release from cluster

Revision History Example

Rev 1

install

→

Rev 2

upgrade

→

Rev 3

upgrade

→

Rev 4

rollback→2

helm history my-release shows all revisions

Other Useful Commands

helm list — List all releases

helm status my-release — Show release info

helm template ./chart — Render locally (dry run)

helm lint ./chart — Validate chart

helm dependency update — Pull sub-charts

helm package ./chart — Create .tgz archive

Go Templating in Helm

Helm uses Go's text/template with Sprig functions for powerful manifest generation.

Value Injection

Template

replicas: {{ .Values.replicaCount }}
image: {{ .Values.image.repo }}

Rendered

replicas: 3
image: myapp:v2.1.0

Conditionals

Template

{{- if .Values.ingress.enabled }}
apiVersion: networking.k8s.io/v1
kind: Ingress
  ...
{{- end }}

Rendered

# ingress.enabled = true
apiVersion: networking.k8s.io/v1
kind: Ingress
  ...

Loops

Template

{{- range .Values.env }}
- name: {{ .name }}
  value: {{ .value | quote }}
{{- end }}

Rendered

- name: DB_HOST
  value: "postgres.svc"
- name: LOG_LEVEL
  value: "info"

Named Templates (_helpers.tpl)

Template

{{/* _helpers.tpl */}}
{{- define "mychart.labels" -}}
app: {{ .Chart.Name }}
version: {{ .Chart.AppVersion }}
{{- end }}

{{/* usage in template */}}
labels:
  {{- include "mychart.labels" . | nindent 4 }}

Rendered

labels:
    app: my-app
    version: 3.1.0

Built-in Objects

.Values Values from values.yaml and overrides .Chart Chart.yaml metadata (Name, Version, etc.) .Release Release info (Name, Namespace, Revision) .Template Current template file info .Capabilities K8s cluster capabilities & API versions

Helm Charts Explained

What is Helm?

Three Core Concepts

Chart Directory Structure

How Helm Renders & Deploys

Release Lifecycle

Go Templating in Helm

Related Topics

Kustomize

GCP IAM

RabbitMQ