Background

The CLI's code for running healthchecks, creating k8s clients, and public API clients has evolved organically. Much of it currently lives in:

• https://github.com/linkerd/linkerd2/blob/c56766a923a07e7eebb4d92f2cc305d7e77407e9/cli/cmd/public_api.go
• https://github.com/linkerd/linkerd2/blob/c56766a923a07e7eebb4d92f2cc305d7e77407e9/pkg/healthcheck/healthcheck.go

Proposal

Reevaluate the underlying APIs provided to the CLI, with these basic use cases:

• Consolidate k8s APIs #2747 create a k8s client (maybe strictly a clientset, consider deprecating KubernetesAPI?)
• create a public API client
• run some arbitrary set of healthchecks
• use cobra.SilenceUsage, so we can return errors from RunE, rather than calling os.Exit(1) as we do in

  linkerd2/cli/cmd/install.go

  Line 690 in c56766a

  func exitIfClusterExists() {

• move public_api.go out of ./cli/cmd, since it's not really a command

motivated by: #2719 (comment)