Helm Components

  • We have the helm cli.

    • Used for helm actions.

  • Adds charts and installs the objects listed in the charts.

  • A Release is created - a single application instance coming from a helm chart.

    • Within each Release, you can have multiple Revision.

    • After an upgrade or change of replicas etc is made, a new Revision is created.

  • Can find helm charts in a public repository.

  • Helm needs a place to store metadata –> data about data.

    • Helm stores the metadata in the Kubernetes cluster as a Secret.

      • This way the data survives and the cluster survives. Everyone in the team can access it.

  • Charts are a collection of files.

    • By using Charts to install the objects is done.

  • Nginx web server and service to expose it - good Hello World example.

    • In the Nginx example there are two objects –> service.yaml and deployment.yaml.

service.yaml:

apiVersion: v1
kind: Service
metadata:
  name: hello-world
spec:
  type: NodePort
  ports:
    - port: 80
    targetPort: http
    protocol: TCP
    name: http
  selector:
    app: hello-world

deployment.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-world
spec:
  replicas: {{ .Values.replicaCount  }}
  selector:
    matchLabels:
      app: hello-world
  template:
    metadata:
      labels:
        app: hello-world
    spec:
      containers:
        - name: nginx
          image: "{{ .Values.image.repository }}"
          ports:
            - name: http
              containerPort: 80
              protocol: TCP

There is a values.yaml file:

replicaCount: 1

image:
  repository: nginx

  • The image and replicas above are specified in a different form. This is called templating.

  • No need to build charts ourselves.

    • What is a good idea however if configuring values in the downloaded chart.

  • The values.yaml file is where the configurable values are stored.

  • Another good helm install command example: helm install my-site bitnami/wordpress

  • The syntax is helm install [release-name][chart-name]

  • Why have a release name?

    • This allows us to install multiple releases, based on the same chart.

      • Can have another site –> helm install my-SECOND-site bitnami/wordpress

        • Therefore you can have two separate sites that are different entities.

    • A good example is a release of a customer-facing website and the other version which is internal and only visible by the developers.

      • Since the two releases are on the same chart, they can transfer any changes over to the customer-facing application and it looks good.

  • What if we want to deploy a new chart? Good helm chart repositories:

    • Appscode
    • TrueCharts
    • Bitnami

    • Community Operators

      • All of the above repositories have listed their charts in a single repository –> ArtifactHub.io.

      • The Official stamped charts are the best ones to use.

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