Helm Chart and Templates
Helm Chart
A Helm chart is simply a collection of templates plus a couple of extra metadata and default config value files which represents an application to be deployed.
- Some charts are designed to deploy a simple application.
- Ohers can be much more complex, with multiple microservices
Helm Chart Directory Structure
To create a Helm chart, run:
helm create <chart-name>
This will generate the following directory structure:
└── app-tier
├── Chart.yml
├── charts
├── templates
│ ├── NOTES.txt
│ ├── _helpers.tpl
│ ├── deployment.yml
│ ├── hpa.yaml
│ ├── ingress.yaml
│ ├── service.yaml
│ ├── serviceaccount.yaml
│ └── tests
│ └── test-connection.yaml
└── values.yaml
Templates Folder
The templates folder is where all the template files for defining Kubernetes resources are stored together.
- Each file typically defines a single resource.
- Helps organize resources into separate, reusable templates.
chart.yaml
The Chart.yaml contains top-level metadata which explains the purpose of the chart. This includes the name and other details of the chart.
-
type: application
When "type" is set to "application", chart becomes deployable and resources are created within the cluster.
-
type: library
When "type" is set to "library", the chart will host reusable functions that can be used with other charts
Sample manifest:
apiVersion: v2
name: sample-app
description: Custom chart of sample app
type: application
version: 1.1.0
appVersion: 1.0.3
values.yaml
The values.yaml defines a structured list of default values that are injected onto the chart templates that reference them during deployment.
Sample values.yaml:
replicaCount: 1
image:
repositoryL nginx
pullPolicy: IfNotPresent
serviceAccount:
name: "app-svc"
create: true
annotations: {}
service:
type: ClusterIP
port: 80
You can override values with helm upgrade. In the example below, the service port is changed from 80 to 8081.
helm upgrade sample-app ./app-tier --set=service.port=8081
Packaging the Chart
Once you're done with the development of the chart, you can now package it by running:
helm package <chart-directory>
Going back to the directory structure from above, we can package the entire directory and label it as "app-tier" as it is the top-level directory that contains the chart.
└── app-tier
├── Chart.yml
├── charts
├── templates
│ ├── NOTES.txt
│ ├── _helpers.tpl
│ ├── deployment.yml
│ ├── hpa.yaml
│ ├── ingress.yaml
│ ├── service.yaml
│ ├── serviceaccount.yaml
│ └── tests
│ └── test-connection.yaml
└── values.yaml
To package this chart, we can run:
helm package app-tier
This will then produce an archive file that used the name and version defined in the Chart.yaml file:
apiVersion: v2
name: sample-app
description: Custom chart of sample app
type: application
version: 1.1.0
appVersion: 1.0.3
Thus the archive file will be named:
sample-app-1.1.0.tgz
Sharing the Chart
The archived file can be shared with anyone. They can be installed simply by running:
helm install <package-name> <chart>
In our case:
helm install app-tier sample-app-1.1.0.tgz
To perform a dry-run installation:
helm install app-tier sample-app-1.1.0.tgz --dry-run
Hosting the Chart
To host the chart in a repository, create an index file:
helm repo index .
This generates an index.yaml file. You can then search the repository:
helm search repo app-tier