Helm is a package manager for Charts.
You might already be familiar with package managers like the ones used for Linux distributions (apt, yum, etc.). In Linux, a package manager takes care of installing, updating, configuring and removing packages from a machine. Helm does something similar, but with Kubernetes applications.
Charts are a set of files that describe a Kubernetes application. These files must be laid out in a folder structure that follows a convention that looks like this:
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.
├── Chart.yaml
├── templates
│ └── application.yaml
└── values.yaml
The Chart.yaml contains some information about the Chart. It looks something like this:
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apiVersion: v2
name: example-helm
description: A Helm chart for an example application
type: application
version: 0.1.0
appVersion: "1.16.0"
values.yaml contains values that are combined with templates to generate valid Kubernetes manifest files. It can look something like this:
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replicaCount: 1
The templates directory contains files that will be processed by Helm’s template engine to generate Kubernetes files. Template files use Go’s templating language, extended with sprig and other specialized functions.
We could have a file named application.yaml inside our templates folder with something like this:
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apiVersion: apps/v1
kind: Deployment
metadata:
name: echo-server-deployment
spec:
selector:
matchLabels:
app: echo-server-deployment
replicas: {{ .Values.replicaCount }}
template:
metadata:
labels:
app: echo-server-deployment
spec:
containers:
- image: ealen/echo-server
name: echo-server
The file is a pretty standard Kubernetes manifest file, except for the replicas: {{ .Values.replicaCount }}. This line will replace the template part with the replicaCount from our values.yaml file.
Before we can use our Chart, we need the Helm CLI.
Helm CLI
The Helm CLI is the brains of Helm. It takes care of parsing, publishing and deploying Charts.
The Helm Installation Guide has the most up-to-date instructions for installing the Helm CLI. At the time of this writing, this command is enough:
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curl https://raw.githubusercontent.com/helm/helm/main/scripts/get-helm-3 | bash
We can verify the install completed correctly with this command:
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helm version
Working with Charts
Now that we have the Helm CLI installed, we can start playing with Charts. We can bootstrap a Chart with this command:
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helm create test-chart
This creates a folder named test-chart with some files we need to create Chart. We can check if the Chart has any problems by changing into the Chart folder and running this command:
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helm lint
We can create a very simple Chart by adding this content to Chart.yaml:
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apiVersion: v2
name: test-chart
description: A tiny test application
type: application
version: 0.1.0
appVersion: "1"
Set values.yaml to:
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replicaCount: 1
And create a templates/application.yaml file with this content:
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apiVersion: apps/v1
kind: Deployment
metadata:
name: echo-server-deployment
spec:
selector:
matchLabels:
app: echo-server-deployment
replicas: {{ .Values.replicaCount }}
template:
metadata:
labels:
app: echo-server-deployment
spec:
containers:
- image: ealen/echo-server
name: echo-server
We can delete everything else.
Now that we have our Chart, we can inspect how the compiled templates will look like:
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helm template .
---
# Source: test-chart/templates/application.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: echo-server-deployment
spec:
selector:
matchLabels:
app: echo-server-deployment
replicas: 1
template:
metadata:
labels:
app: echo-server-deployment
spec:
containers:
- image: ealen/echo-server
name: echo-server
We can see that replicas is set to 1 as specified in values.yaml.
If we have kubectl installed and configured, we can install our Chart to our cluster:
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helm install . --generate-name
We can see all our helm deployments with:
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helm list
NAME NAMESPACE REVISION UPDATED STATUS CHART APP VERSION
chart-1637726261 default 1 2021-11-23 22:57:48.127492259 -0500 EST deployed test-chart-0.1.0 1
Let’s update the number of replicas in values.yaml:
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replicaCount: 2
We can now update our Chart deployment:
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helm upgrade chart-1637726261 .
And we’ll see that our Chart now has 2 replicas:
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helm get manifest chart-1637726261
---
# Source: test-chart/templates/application.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: echo-server-deployment
spec:
selector:
matchLabels:
app: echo-server-deployment
replicas: 2
template:
metadata:
labels:
app: echo-server-deployment
spec:
containers:
- image: ealen/echo-server
name: echo-server
Finally, we can delete our Chart with this command:
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helm uninstall chart-1637726261
Working with repositories
Besides using our own Charts, there are repositories where we can find open source Charts that are ready to use.
We can use the Helm CLI to search for available Charts in ArtifactHub. Let’s say we are looking for a Chart for a node application:
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helm search hub node -o yaml
- app_version: 16.13.0
description: Event-driven I/O server-side JavaScript environment based on V8
url: https://artifacthub.io/packages/helm/bitnami-aks/node
version: 16.0.1
- app_version: 16.13.0
description: Event-driven I/O server-side JavaScript environment based on V8
url: https://artifacthub.io/packages/helm/bitnami/node
version: 16.0.1
...
The output is a list of Charts that match the node keyword.
The URL included in each result is a link to the Chart in ArtifactHub. It can be used to learn more about the Chart and currently is the only way to know which repo a Chart is in.
AftifactHub is website that allows us to search multiple repositories for Charts. A repository is where the Chart is actually hosted.
If we go to https://artifacthub.io/packages/helm/bitnami/node we’ll find an INSTALL button that will give us instructions to install the repo:
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helm repo add bitnami https://charts.bitnami.com/bitnami
Once our repo is installed, we can install the Chart in our cluster:
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helm install bitnami/node --generate-name
The Chart will be installed, the same way our own Chart was installed. We can see the Chart using helm list:
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helm list
NAME NAMESPACE REVISION UPDATED STATUS CHART APP VERSION
node-1637284508 default 1 2021-11-18 20:15:20.849604214 -0500 EST deployed node-16.0.1 16.13.0
Conclusion
In this article we learned how to create a simple Chart and consume Charts from a repository. While doing this we got familiar with the basic operations available in the helm CLI.
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