remove mentions of kube-dns in kubeadm docs

content/en/docs/tasks/administer-cluster/coredns.md

@@ -36,7 +36,7 @@ For manual deployment or replacement of kube-dns, see the documentation at the
 
 In Kubernetes version 1.10 and later, you can also move to CoreDNS when you use `kubeadm` to upgrade
 a cluster that is using `kube-dns`. In this case, `kubeadm` will generate the CoreDNS configuration
-("Corefile") based upon the `kube-dns` ConfigMap, preserving configurations for federation,
+("Corefile") based upon the `kube-dns` ConfigMap, preserving configurations for
 stub domains, and upstream name server.
 
 If you are moving from kube-dns to CoreDNS, make sure to set the `CoreDNS` feature gate to `true`
@@ -46,8 +46,7 @@ kubeadm upgrade apply v1.11.0 --feature-gates=CoreDNS=true
 ```
 
 In Kubernetes version 1.13 and later the `CoreDNS` feature gate is removed and CoreDNS
-is used by default. Follow the guide outlined [here](/docs/reference/setup-tools/kubeadm/kubeadm-init-phase#cmd-phase-addon) if you want
-your upgraded cluster to use kube-dns.
+is used by default.
 
 In versions prior to 1.11 the Corefile will be **overwritten** by the one created during upgrade.
 **You should save your existing ConfigMap if you have customized it.** You may re-apply your
@@ -56,26 +55,7 @@ customizations after the new ConfigMap is up and running.
 If you are running CoreDNS in Kubernetes version 1.11 and later, during upgrade,
 your existing Corefile will be retained.
 
-
-### Installing kube-dns instead of CoreDNS with kubeadm
-
-{{< note >}}
-In Kubernetes 1.11, CoreDNS has graduated to General Availability (GA)
-and is installed by default.
-{{< /note >}}
-
-{{< warning >}}
-In Kubernetes 1.18, kube-dns usage with kubeadm has been deprecated and will be removed in a future version.
-{{< /warning >}}
-
-To install kube-dns on versions prior to 1.13, set the `CoreDNS` feature gate
-value to `false`:
-
-```
-kubeadm init --feature-gates=CoreDNS=false
-```
-
-For versions 1.13 and later, follow the guide outlined [here](/docs/reference/setup-tools/kubeadm/kubeadm-init-phase#cmd-phase-addon).
+In Kubernetes version 1.21, support for `kube-dns` is removed from kubeadm.
 
 ## Upgrading CoreDNS
 

content/en/docs/tasks/administer-cluster/dns-custom-nameservers.md

@@ -34,7 +34,7 @@ As of Kubernetes v1.12, CoreDNS is the recommended DNS Server, replacing kube-dn
 originally used kube-dns, you may still have `kube-dns` deployed rather than CoreDNS.
 
 {{< note >}}
-Both the CoreDNS and kube-dns Service are named `kube-dns` in the `metadata.name` field.  
+The CoreDNS Service is named `kube-dns` in the `metadata.name` field.  
 This is so that there is greater interoperability with workloads that relied on the legacy `kube-dns` Service name to resolve addresses internal to the cluster. Using a Service named `kube-dns` abstracts away the implementation detail of which DNS provider is running behind that common name.
 {{< /note >}}
 
@@ -179,17 +179,14 @@ During translation, all FQDN nameservers will be omitted from the CoreDNS config
 
 CoreDNS supports the features of kube-dns and more.
 A ConfigMap created for kube-dns to support `StubDomains`and `upstreamNameservers` translates to the `forward` plugin in CoreDNS.
-Similarly, the `Federations` plugin in kube-dns translates to the `federation` plugin in CoreDNS.
 
 ### Example
 
-This example ConfigMap for kube-dns specifies federations, stubdomains and upstreamnameservers:
+This example ConfigMap for kube-dns specifies stubdomains and upstreamnameservers:
 
 ```yaml
 apiVersion: v1
 data:
-  federations: |
-    {"foo" : "foo.feddomain.com"}
   stubDomains: |
     {"abc.com" : ["1.2.3.4"], "my.cluster.local" : ["2.3.4.5"]}
   upstreamNameservers: |
@@ -199,13 +196,6 @@ kind: ConfigMap
 
 The equivalent configuration in CoreDNS creates a Corefile:
 
-* For federations:
-```
-federation cluster.local {
-    foo foo.feddomain.com
-}
-```
-
 * For stubDomains:
 ```yaml
 abc.com:53 {

content/en/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade.md

@@ -328,7 +328,7 @@ and post-upgrade manifest file for a certain component, a backup file for it wil
 - Makes sure the control plane images are available or available to pull to the machine.
 - Generates replacements and/or uses user supplied overwrites if component configs require version upgrades.
 - Upgrades the control plane components or rollbacks if any of them fails to come up.
-- Applies the new `kube-dns` and `kube-proxy` manifests and makes sure that all necessary RBAC rules are created.
+- Applies the new `CoreDNS` and `kube-proxy` manifests and makes sure that all necessary RBAC rules are created.
 - Creates new certificate and key files of the API server and backs up old files if they're about to expire in 180 days.
 
 `kubeadm upgrade node` does the following on additional control plane nodes: