DevOps

Helm

Helm is a package manager for Kubernetes: an application is packaged as a chart with templates and configured through values.

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What it is

Helm is called the package manager for Kubernetes. Instead of a dozen YAML files you install one chart: a package with manifest templates and a values.yaml file of parameters.

helm install renders the templates with your values and applies the result to the cluster as a release. helm upgrade updates it and helm rollback reverts, because Helm keeps release history. Charts are published in repositories and OCI registries.

Helm is a CNCF project with graduated status (2020). Alternatives for templating manifests: Kustomize (built into kubectl) and rendering through GitOps tools.

Use it when

  • You install ready-made apps into Kubernetes: Prometheus, Postgres, an ingress controller.
  • You deploy one app to several environments with different parameters.
  • You need versioning, upgrades and rollback of packages.

Avoid it when

  • You have a few simple manifests: Kustomize or plain kubectl apply are simpler.
  • Go templates become unreadable: reconsider the approach.

Key concepts

Chart
A Helm package: templates, default values and metadata.
Release
A specific installation of a chart in a cluster with its own name and history.
values.yaml
Parameters injected into templates; override them with --set or -f.
Repository / OCI
Where charts are published: an HTTP repository or a container registry.

Example

Installing a chart from a repository, upgrading with your values and rolling back.

Interview questions

  1. 1. What are a chart and a release?

    A chart is a package with templates and values. A release is a specific installation of that chart in a cluster. One chart can produce many releases with different parameters.

  2. 2. How do you roll back in Helm?

    Helm stores release revisions, so helm rollback <release> <revision> restores the previous state. helm history lists the revisions.

  3. 3. Helm or Kustomize?

    Helm gives templates, packaging and versioning, good for distribution. Kustomize patches plain YAML without templates, simpler for your own manifests. They are often combined.

Interview questions from the bank

Related technologies

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