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HELM

HELM is a package manager for Kubernetes. It simplifies deploying, upgrading and managing Kubernetes application.

Main concepts

Chart contains all the Kubernetes manifests needed to deploy an app.

Structure of a chart:

  • Chart.yaml : metadata (name, version, description)
  • values.yaml : default configuration values
  • templates/ : parameterized Kubernetes YAML files

HELM uses Go templating {{ ... }} to generate Kubernetes manifests dynamically.

Getting started

1. Install HELM cli
2. Setup HELM charts in a project with the command helm create

This command creates a chart directory along with the common files and directories used in a chart.

For example :

helm create devops/helm

It will create a directory structure that looks something like this:

devops/helm
├── .helmignore    # Contains patterns to ignore when packaging Helm charts.
├── Chart.yaml     # Information about your chart
├── values.yaml    # The default values for your templates
├── charts/        # Charts that this chart depends on
└── templates/     # The template files
    └── tests/     # The test files
3. Setup your templates

Define your Kubernetes manifests in the HELM chart that you have just created.

So under devops/helm (our previous created chart), you will define under /templates/ the manifests :

  • deployment.yaml
  • service.yaml
  • ingress.yaml
  • ...

Let's take an example of a manifest : deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: {{ .Values.app }}-{{ .Values.env }}
  labels:
    app.kubernetes.io/name: {{ .Values.app }}-{{ .Values.env }}
    app.kubernetes.io/component: {{ .Values.app }}-{{ .Values.env }}
    environment: {{ .Values.env }}
spec:
  replicas: {{ .Values.replicas }}
  selector:
    matchLabels:
    app.kubernetes.io/name: {{ .Values.app }}-{{ .Values.env }}
    app.kubernetes.io/component: {{ .Values.app }}-{{ .Values.env }}
  strategy:
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0
  template:
    metadata:
      labels:
        app.kubernetes.io/name: {{ .Values.app }}-{{ .Values.env }}
        app.kubernetes.io/component: {{ .Values.app }}-{{ .Values.env }}
        environment: {{ .Values.env }}
    spec:
      containers:
        - image: https://hub.docker.com/my-namespace/{{ .Values.app }}:{{ .Values.tag }}
          imagePullPolicy: Always
          name : {{ .Values.app }}-{{ .Values.env }}-cn
          resources:
            limits:
              cpu: {{ .Values.resources.limits.cpu }}
              memory: {{ .Values.resources.limits.memory }}
            requests:
              cpu: {{ .Values.resources.requests.cpu }}
              memory: {{ .Values.resources.requests.memory }}
            # ... simplified for documentation purpose
        {{- if .Values.filebeat.enabled }}
        - image: https://hub.docker.com/elastic/filebeat:8.19.2
          imagePullPolicy: Always
          name : {{ .Values.app }}-{{ .Values.env }}-filebeat-cn
          resources:
            limits:
              cpu: 20m
              memory: 200Mi
            requests:
              cpu: 5m
              memory: 200Mi
            # ... simplified for documentation purpose
        {{- end }}
4. Configuration via values.yaml

The values.yaml file allows you to centralize and override configurations without editing your template files directly.

Here is an example of a values.yaml for the app audit

  • HOMOL environment values : /audit/devops/homol/values.yaml
app: audit
env: homol
replicas: 1

resources:
  limits:
    cpu: 200m
    memory: 200Mi
  requests:
    cpu: 50m
    memory: 200Mi

filebeat:
  enabled: false
  • PROD environment values : /audit/devops/prod/values.yaml
app: audit
env: prod
replicas: 2

resources:
  limits:
    cpu: 500m
    memory: 500Mi
  requests:
    cpu: 200m
    memory: 500Mi

filebeat:
  enabled: true
5. Deployment

Traditionally you would have used kubectl to deploy to a Kubernetes cluster, by using the command kubectl apply

Now that you are using HELM you would need to switch that up to use HELM cli upgrade command :

helm upgrade --install ${app} devops/helm \
     -f audit/devops/${env}/values.yaml
     --set image.tag=${tag}
     --namespace=${namespace}
     --wait

The tag value is being passed during deployment time, since the image tag will change everytime you build/push an docker image into your registry

Attention point

If you have existing Kubernetes manifests in a cluster, and wan to migrate them to use a HELM chart, you will need to add some labels and annotations prior to the migration.

HELM won't know how to manage an existing Kubernetes manifests without the following :

labels :

app.kubernetes.io/managed-by: Helm

annotations :

meta.helm.sh/release-name: ...
meta.helm.sh/release-namespace: ...

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