Change:
For GKE kubernetes cluster it won't let you join the cluster if you don't create a for your currently active account email () in a next manner: Please, add this in the docs.

Discussion:
## Adding a cluster to a federation <del> Once you've deployed a federation control plane, you'll need to make that control plane aware of the clusters it should manage. You can add a cluster to your federation by using the [`kubefed join`](/docs/admin/kubefed_join/) command. A new context will have been added to your kubeconfig named `fellowship` (after the name of your federation). To join clusters into the federation, you will need to change the context. </del> <ins> After you've deployed a federation control plane, you'll need to make that control plane aware of the clusters it should manage. </ins> <del> ``` kubectl config use-context fellowship ``` </del> <ins> To join clusters into the federation: </ins> <del> To use `kubefed join`, you'll need to provide the name of the cluster you want to add to the federation, and the `--host-cluster-context` for the federation control plane's host cluster. </del> <ins> 1. Change the context: </ins> <del> > Note: The name that you provide to the `join` command is used as the joining cluster's identity in federation. This name should adhere to the rules described in the [identifiers doc](/docs/concepts/overview/working-with-objects/names/). If the context corresponding to your joining cluster conforms to these rules then you can use the same name in the join command. Otherwise, you will have to choose a different name for your cluster's identity. For more information, please see the [naming rules and customization](#naming-rules-and-customization) section below. </del> <ins> kubectl config use-context fellowship </ins> <del> The following example command adds the cluster `gondor` to the federation running on host cluster `rivendell`: </del> <ins> 1. If you are using a managed cluster service, allow the service to access the cluster. To do this, create a `clusterrolebinding` for the account associated with your cluster service: </ins> <del> ``` kubefed join gondor --host-cluster-context=rivendell ``` </del> <ins> kubectl create clusterrolebinding <your_user>-cluster-admin-binding --clusterrole=cluster-admin --user=<your_user>@example.org --context=<joining_cluster_context 1. Join the cluster to the federation, using `kubefed join`, and make sure you provide the following: * The name of the cluster that you are joining to the federation * `--host-cluster-context`, the kubeconfig context for the host cluster For example, this command adds the cluster `gondor` to the federation running on host cluster `rivendell`: ``` kubefed join gondor --host-cluster-context=rivendell ``` A new context has now been added to your kubeconfig named `fellowship` (after the name of your federation). > Note: The name that you provide to the `join` command is used as the joining cluster's identity in federation. If this name adheres to the rules described in the [identifiers doc](/docs/concepts/overview/working-with-objects/names/). If the context corresponding to your joining cluster conforms to these rules then you can use the same name in the join command. Otherwise, you will have to choose a different name for your cluster's identity. </ins> <del> > Note: Kubernetes requires that you manually join clusters to a federation because the federation control plane manages only those clusters that it is responsible for managing. Adding a cluster tells the federation control plane that it is responsible for managing that cluster. </del> ### Naming rules and customization