Helm in Practice

Handling Custom Resource Definitions (CRDs) in Helm

Custom Resource Definitions are cluster-wide extensions of the Kubernetes API. Helm treats them specially because CRDs must be installed before any custom resources that depend on them can be created.

Charts can include a top-level crds/ directory to hold CRD YAML files. When you run a helm install for such a chart, Helm will automatically install the CRD objects first, before rendering or installing the rest of the templates. These CRD files are not templated (no {{ }} expressions are allowed in crds/).

If a CRD already exists in the cluster, Helm skips installing it and prints a warning instead.

For example, the kube-prometheus-stack chart includes several CRDs for Prometheus and Alertmanager.

# Add the repository
helm repo add prometheus-community \
  https://prometheus-community.github.io/helm-charts

# Pull the chart
cd $HOME/
helm pull prometheus-community/kube-prometheus-stack --untar --version 79.12.0

# Inspect the crds/ directory
ls kube-prometheus-stack/charts/crds/

You can use --skip-crds if you want to prevent Helm from installing CRDs. This is useful if you want to manage CRDs separately or if they are already installed in the cluster.

# Dry run if you want to see what would happen