Helm

yamlrelease

Helm is the package manager for Kubernetes. A chart is a templated bundle of manifests, an install of a chart into a cluster is a release, and each change produces a numbered revision you can roll back to. Helm 3 talks to the cluster directly (no more Tiller). Commands below checked with helm v3.21.3.

A chart’s structure

helm create mychart

scaffolds:

mychart/
  Chart.yaml          # name, version, appVersion
  values.yaml         # default values, overridable at install time
  .helmignore
  charts/             # vendored subcharts, empty at first
  templates/
    deployment.yaml
    service.yaml
    serviceaccount.yaml
    ingress.yaml
    httproute.yaml    # Gateway API route, disabled by default
    hpa.yaml
    NOTES.txt         # message printed after install
    _helpers.tpl      # reusable template snippets
    tests/
      test-connection.yaml   # a pod run by: helm test <release>

Templates are Go templates; {{ .Values.foo }} pulls from values.yaml (or from overrides at install time).

Two files in that scaffold are opt-in rather than always applied, in two different ways. httproute.yaml is the Gateway API counterpart of the ingress and stays behind httpRoute.enabled: false in values.yaml, so a plain render omits it entirely. templates/tests/ holds manifests annotated "helm.sh/hook": test: helm template still prints them, but being hooks they are not created on install, only when you call helm test <release> against a live cluster.

Render and lint locally (no cluster needed)

This is the fast feedback loop while writing a chart:

helm lint mychart                       # static checks
helm template myrelease mychart         # render manifests to stdout, no cluster
helm template myrelease mychart --set replicaCount=3   # override a value
helm template myrelease mychart -f prod-values.yaml    # override with a file
helm show chart mychart                 # Chart.yaml metadata
helm show values mychart                # the default values

helm template is the honest way to see exactly what will be applied before touching a cluster.

Install, upgrade, roll back

Against a cluster (uses the current kubectl context and namespace):

helm install myrelease mychart                  # install a release
helm install myrelease mychart -f prod-values.yaml --set image.tag=1.4.2
helm upgrade --install myrelease mychart        # create or update (idempotent)
helm list -A                                    # releases across all namespaces
helm history myrelease                          # revisions of a release
helm rollback myrelease 2                       # roll back to revision 2
helm uninstall myrelease                        # remove the release
helm status myrelease                           # current state and notes
helm get values myrelease                       # values a release was installed with

helm upgrade --install is the usual CI/CD form: it installs on first run and upgrades afterwards.

Repositories

helm repo add <name> <url>              # e.g. bitnami https://charts.bitnami.com/bitnami
helm repo update                        # refresh the local index
helm search repo <term>                 # find charts
helm show values <name>/<chart>         # inspect before installing
helm install myrelease <name>/<chart> -f my-values.yaml

Artifact Hub indexes public charts.

See also

Related