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Custom Resource Definitions

This section of the Best Practices Guide deals with creating and using Custom Resource Definition objects.

When working with Custom Resource Definitions (CRDs), it is important to distinguish two different pieces:

  • There is a declaration of a CRD. This is the YAML file that has the kind CustomResourceDefinition
  • Then there are resources that use the CRD. Say a CRD defines foo.example.com/v1. Any resource that has apiVersion: example.com/v1 and kind Foo is a resource that uses the CRD.

Install a CRD Declaration Before Using the Resource

Helm is optimized to load as many resources into Kubernetes as fast as possible. By design, Kubernetes can take an entire set of manifests and bring them all online (this is called the reconciliation loop).

But there’s a difference with CRDs.

For a CRD, the declaration must be registered before any resources of that CRDs kind(s) can be used. And the registration process sometimes takes a few seconds.

Method 1: Separate Charts

One way to do this is to put the CRD definition in one chart, and then put any resources that use that CRD in another chart.

In this method, each chart must be installed separately.

Method 2: Pre-install Hooks

To package the two together, add a pre-install hook to the CRD definition so that it is fully installed before the rest of the chart is executed.

Note that if you create the CRD with a pre-install hook, that CRD definition will not be uninstalled when helm uninstall is run.