istio.io/content/help/faq/setup/k8s-checking-cluster-alpha-features.md

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Kubernetes - How do I check if my cluster has enabled the alpha features required for automatic sidecar injection?	10

Automatic sidecar injection requires the initializer alpha feature. Run the following command to check if the initializer has been enabled (empty output indicates that initializers are not enabled):

$ kubectl api-versions | grep admissionregistration

In addition, the Kubernetes API server must be started with the Initializer plugin enabled. Failure to enable the Initializer plugin will result in the following error when trying to create the initializer deployment.

The Deployment "istio-initializer" is invalid: metadata.initializers.pending: Invalid value: "null": must be non-empty when result is not set