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
- Then there are resources that use the CRD. Say a CRD defines
foo.example.com/v1. Any resource that has
apiVersion: example.com/v1and kind
Foois 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.