kubeadm-setup: add page about control plane flags (#9067)

This page adds instructions on how to use the kubeadm config
to pass flags to control plane components.

The provided examples are pretty basic. Later this can be expanded with
actual user stories.

content/en/docs/setup/independent/control-plane-flags.md

@@ -0,0 +1,81 @@
+---
+reviewers:
+- sig-cluster-lifecycle
+title: Customizing control plane configuration with kubeadm
+content_template: templates/concept
+weight: 50
+---
+
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+
+kubeadm’s configuration exposes the following fields that can be used to override the default flags passed to control plane components such as the APIServer, ControllerManager and Scheduler:
+
+- `APIServerExtraArgs`
+- `ControllerManagerExtraArgs`
+- `SchedulerExtraArgs`
+
+These fields consist of `key: value` pairs. To override a flag for a control plane component:
+
+1.  Add the appropriate field to your configuration.
+2.  Add the flags to override to the field.
+
+For more details on each field in the configuration you can navigate to our
+[API reference pages](https://godoc.org/k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm#MasterConfiguration).
+
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+
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+
+## APIServer flags
+
+For details, see the [reference documentation for kube-apiserver](https://kubernetes.io/docs/reference/command-line-tools-reference/kube-apiserver/).
+
+Example usage:
+```yaml
+apiVersion: kubeadm.k8s.io/v1alpha2
+kind: MasterConfiguration
+kubernetesVersion: v1.11.0
+metadata:
+  name: 1.11-sample
+apiServerExtraArgs:
+  advertise-address: 192.168.0.103
+  anonymous-auth: false
+  enable-admission-plugins: AlwaysPullImages,DefaultStorageClass
+  audit-log-path: /home/johndoe/audit.log
+```
+
+## ControllerManager flags
+
+For details, see the [reference documentation for kube-controller-manager](https://kubernetes.io/docs/reference/command-line-tools-reference/kube-controller-manager/).
+
+Example usage:
+```yaml
+apiVersion: kubeadm.k8s.io/v1alpha2
+kind: MasterConfiguration
+kubernetesVersion: v1.11.0
+metadata:
+  name: 1.11-sample
+controllerManagerExtraArgs:
+  cluster-signing-key-file: /home/johndoe/keys/ca.key
+  bind-address: 0.0.0.0
+  deployment-controller-sync-period: 50
+```
+
+## Scheduler flags
+
+For details, see the [reference documentation for kube-scheduler](https://kubernetes.io/docs/reference/command-line-tools-reference/kube-scheduler/).
+
+Example usage:
+```yaml
+apiVersion: kubeadm.k8s.io/v1alpha2
+kind: MasterConfiguration
+kubernetesVersion: v1.11.0
+metadata:
+  name: 1.11-sample
+schedulerExtraArgs:
+  address: 0.0.0.0
+  config: /home/johndoe/schedconfig.yaml
+  kubeconfig: /home/johndoe/kubeconfig.yaml
+```
+
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