Revise callouts for kubeadm cert page

Use fewer note and warning blocks, to keep the important messages
focused.

Author: Tim Bannister

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

@@ -19,6 +19,11 @@ to kubeadm certificate management.
 
 You should be familiar with [PKI certificates and requirements in Kubernetes](/docs/setup/best-practices/certificates/).
 
+This guide covers the usage of the `openssl` command (used for manual certificate signing,
+if you choose that approach), but you can use your preferred tools.
+
+Some of the steps here use `sudo` for administrator access. You can use any equivalent tool.
+
 <!-- steps -->
 
 ## Using custom certificates {#custom-certificates}
@@ -53,6 +58,9 @@ There are various ways to prepare the component credentials when using external
 [PKI certificates and requirements](/docs/setup/best-practices/certificates/) includes information
 on how to prepare all the required by kubeadm component credentials manually.
 
+This guide covers the usage of the `openssl` command (used for manual certificate signing,
+if you choose that approach), but you can use your preferred tools.
+
 ### Preparation of credentials by signing CSRs generated by kubeadm
 
 kubeadm can [generate CSR files](#signing-csr) that you can sign manually with tools like
@@ -87,7 +95,11 @@ Once the credentials are prepared on all nodes, call `kubeadm init` and `kubeadm
 join the cluster. kubeadm will use the existing kubeconfig and certificate files under `/etc/kubernetes/`
 and its `pki` sub directory.
 
-## Check certificate expiration
+## Certificate expiry and management {#check-certificate-expiration}
+
+{{< note >}}
+`kubeadm` cannot manage certificates signed by an external CA.
+{{< /note >}}
 
 You can use the `check-expiration` subcommand to check when certificates expire:
 
@@ -123,20 +135,15 @@ by kubeadm (`admin.conf`, `controller-manager.conf` and `scheduler.conf`).
 Additionally, kubeadm informs the user if the certificate is externally managed; in this case, the
 user should take care of managing certificate renewal manually/using other tools.
 
-{{< warning >}}
-`kubeadm` cannot manage certificates signed by an external CA.
-{{< /warning >}}
-
-{{< note >}}
-`kubelet.conf` is not included in the list above because kubeadm configures kubelet
+The `kubelet.conf` configuration file is not included in the list above because kubeadm
+configures kubelet
 for [automatic certificate renewal](/docs/tasks/tls/certificate-rotation/)
 with rotatable certificates under `/var/lib/kubelet/pki`.
 To repair an expired kubelet client certificate see
 [Kubelet client certificate rotation fails](/docs/setup/production-environment/tools/kubeadm/troubleshooting-kubeadm/#kubelet-client-cert).
-{{< /note >}}
 
-{{< warning >}}
-On nodes created with `kubeadm init`, prior to kubeadm version 1.17, there is a
+{{< note >}}
+On nodes created with `kubeadm init` from versions prior to kubeadm version 1.17, there is a
 [bug](https://github.com/kubernetes/kubeadm/issues/1753) where you manually have to modify the
 contents of `kubelet.conf`. After `kubeadm init` finishes, you should update `kubelet.conf` to
 point to the rotated kubelet client certificates, by replacing `client-certificate-data` and
@@ -146,7 +153,7 @@ point to the rotated kubelet client certificates, by replacing `client-certifica
 client-certificate: /var/lib/kubelet/pki/kubelet-client-current.pem
 client-key: /var/lib/kubelet/pki/kubelet-client-current.pem
 ```
-{{< /warning >}}
+{{< /note >}}
 
 ## Automatic certificate renewal
 
@@ -166,18 +173,20 @@ If you have more complex requirements for certificate renewal, you can opt out f
 behavior by passing `--certificate-renewal=false` to `kubeadm upgrade apply` or to `kubeadm
 upgrade node`.
 
-{{< warning >}}
-Prior to kubeadm version 1.17 there is a [bug](https://github.com/kubernetes/kubeadm/issues/1818)
-where the default value for `--certificate-renewal` is `false` for the `kubeadm upgrade node`
-command. In that case, you should explicitly set `--certificate-renewal=true`.
-{{< /warning >}}
-
 ## Manual certificate renewal
 
-You can renew your certificates manually at any time with the `kubeadm certs renew` command, with the appropriate command line options.
+You can renew your certificates manually at any time with the `kubeadm certs renew` command,
+with the appropriate command line options. If you are running cluster with a replicated control
+plane, this command needs to be executed on all the control-plane nodes.
 
 This command performs the renewal using CA (or front-proxy-CA) certificate and key stored in `/etc/kubernetes/pki`.
 
+`kubeadm certs renew` uses the existing certificates as the authoritative source for attributes
+(Common Name, Organization, subject alternative name) and does not rely on the `kubeadm-config`
+ConfigMap.
+Even so, the Kubernetes project recommends keeping the served certificate and the associated
+values in that ConfigMap synchronized, to avoid any risk of confusion.
+
 After running the command you should restart the control plane Pods. This is required since
 dynamic certificate reload is currently not supported for all components and certificates.
 [Static Pods](/docs/tasks/configure-pod-container/static-pod/) are managed by the local kubelet
@@ -188,33 +197,25 @@ The kubelet will terminate the Pod if it's no longer in the manifest directory.
 You can then move the file back and after another `fileCheckFrequency` period, the kubelet will recreate
 the Pod and the certificate renewal for the component can complete.
 
-{{< warning >}}
-If you are running an HA cluster, this command needs to be executed on all the control-plane nodes.
-{{< /warning >}}
-
-{{< note >}}
-`certs renew` uses the existing certificates as the authoritative source for attributes (Common
-Name, Organization, SAN, etc.) instead of the `kubeadm-config` ConfigMap. It is strongly recommended
-to keep them both in sync.
-{{< /note >}}
-
-`kubeadm certs renew` can renew any specific certificate or, with the subcommand `all`, it can renew all of them, as shown below:
+`kubeadm certs renew` can renew any specific certificate or, with the subcommand `all`, it can renew all of them:
 
 ```shell
+# If you are running cluster with a replicated control plane, this command
+# needs to be executed on all the control-plane nodes.
 kubeadm certs renew all
 ```
 
-{{< note >}}
+### Copying the administrator certificate (optional) {#admin-certificate-copy}
+
 Clusters built with kubeadm often copy the `admin.conf` certificate into
 `$HOME/.kube/config`, as instructed in [Creating a cluster with kubeadm](/docs/setup/production-environment/tools/kubeadm/create-cluster-kubeadm/).
 On such a system, to update the contents of `$HOME/.kube/config`
-after renewing the `admin.conf`, you must run the following commands:
+after renewing the `admin.conf`, you could run the following commands:
 
 ```shell
 sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
 sudo chown $(id -u):$(id -g) $HOME/.kube/config
 ```
-{{< /note >}}
 
 ## Renew certificates with the Kubernetes certificates API
 
@@ -430,16 +431,13 @@ as extra SANs and custom IP addresses must be stored in the same configuration
 file and used for all relevant kubeadm commands by passing it as `--config`.
 
 {{< note >}}
-This guide will cover the usage of the `openssl` command for singing the CSRs,
-but you can use your preferred tools.
-{{< /note >}}
+This guide uses the default Kubernetes directory `/etc/kubernetes`, which requires
+a super user. If you are following this guide and are using directories that you can
+write to (typically, this means running `kubeadm` with `--cert-dir` and `--kubeconfig-dir`)
+then you can omit the `sudo` command).
 
-{{< note >}}
-This guide will use the default Kubernetes directory `/etc/kubernetes`, which requires
-a super user. If you are following this guide with permissive directories
-(by passing `--cert-dir` and `--kubeconfig-dir`) you can omit the `sudo` command).
-But note that the resulted files must be copied to the `/etc/kubernetes` tree,
-so that `kubeadm init` or `kubeadm join` will find them.
+You must then copy the files that you produced over to within the `/etc/kubernetes`
+directory so that `kubeadm init` or `kubeadm join` will find them.
 {{< /note >}}
 
 ### Preparing CA and service account files
@@ -460,8 +458,9 @@ private keys) that kubeadm needs for a control plane node.
 
 {{< note >}}
 If you are using an external CA, you must generate the same files out of band and manually
-copy them to the primary control plane node in `/etc/kubernetes`. Once all CSRs
-are signed, you can delete the root CA key (`ca.key`) as noted in the
+copy them to the primary control plane node in `/etc/kubernetes`.
+
+Once all CSRs are signed, you can delete the root CA key (`ca.key`) as noted in the
 [External CA mode](#external-ca-mode) section.
 {{< /note >}}
 
@@ -500,9 +499,10 @@ That is because the active kube-controller-manager will be responsible
 for signing new kubelet client certificates.
 
 {{< note >}}
-Processing the `kubelet.conf.csr` on the primary control plane node
-(`kubeadm init`) is required, because that is considered the node that
-bootstraps the cluster and a pre-populated `kubelet.conf` is needed.
+You must process the `kubelet.conf.csr` file on the primary control plane node
+(the host where you originally ran `kubeadm init`). This is because `kubeadm`
+considers that as the node that bootstraps the cluster, and a pre-populated
+`kubelet.conf` is needed.
 {{< /note >}}
 
 #### Control plane nodes
@@ -539,8 +539,8 @@ the steps for worker nodes entirely.
 
 {{< note >}}
 If you are using external CA and already have CA serial number files (`.srl`) for
-`openssl` you can copy such files to a kubeadm node where CSRs will be processed.
-`.srl` files to copy are `/etc/kubernetes/pki/ca.srl`,
+`openssl`, you can copy such files to a kubeadm node where CSRs will be processed.
+The `.srl` files to copy are `/etc/kubernetes/pki/ca.srl`,
 `/etc/kubernetes/pki/front-proxy-ca.srl` and `/etc/kubernetes/pki/etcd/ca.srl`.
 The files can be then moved to a new node where CSR files will be processed.