kubeadm: improvements to the cert management documentation (#18397)

neolit123 · k8s-ci-robot · commit f510b223e90e · 2020-01-03T09:45:42.000-08:00
- move the sections about custom certificates and external CA
to the kubeadm-certs page
- minor cleanups to the kubeadm-certs page, including updated output
for the check-expiration command
- link the implementation details page to the new locations
for custom certs and external CA
diff --git a/content/en/docs/reference/setup-tools/kubeadm/implementation-details.md b/content/en/docs/reference/setup-tools/kubeadm/implementation-details.md
@@ -150,12 +150,12 @@ Certificates are stored by default in `/etc/kubernetes/pki`, but this directory
 1. If a given certificate and private key pair both exist, and its content is evaluated compliant with the above specs, the existing files will
    be used and the generation phase for the given certificate skipped. This means the user can, for example, copy an existing CA to
    `/etc/kubernetes/pki/ca.{crt,key}`, and then kubeadm will use those files for signing the rest of the certs.
-   See also [using custom certificates](/docs/reference/setup-tools/kubeadm/kubeadm-init/#custom-certificates)
+   See also [using custom certificates](/docs/tasks/administer-cluster/kubeadm/kubeadm-certs#custom-certificates)
 2. Only for the CA, it is possible to provide the `ca.crt` file but not the `ca.key` file, if all other certificates and kubeconfig files
    already are in place kubeadm recognize this condition and activates the ExternalCA , which also implies the `csrsigner`controller in
    controller-manager won't be started
-3. If kubeadm is running in [ExternalCA mode](/docs/reference/setup-tools/kubeadm/kubeadm-init/#external-ca-mode); all the certificates must be provided by the user,
-   because kubeadm cannot generate them by itself
+3. If kubeadm is running in [external CA mode](/docs/tasks/administer-cluster/kubeadm/kubeadm-certs#external-ca-mode);
+   all the certificates must be provided by the user, because kubeadm cannot generate them by itself
 4. In case of kubeadm is executed in the `--dry-run` mode, certificates files are written in a temporary folder
 5. Certificate generation can be invoked individually with the [`kubeadm init phase certs all`](/docs/reference/setup-tools/kubeadm/kubeadm-init-phase/#cmd-phase-certs) command
 
diff --git a/content/en/docs/reference/setup-tools/kubeadm/kubeadm-init.md b/content/en/docs/reference/setup-tools/kubeadm/kubeadm-init.md
@@ -26,8 +26,7 @@ following steps:
 1. Generates a self-signed CA (or using an existing one if provided) to set up
    identities for each component in the cluster. If the user has provided their
    own CA cert and/or key by dropping it in the cert directory configured via `--cert-dir`
-   (`/etc/kubernetes/pki` by default) this step is skipped as described in the
-   [Using custom certificates](#custom-certificates) document.
+   (`/etc/kubernetes/pki` by default).
    The APIServer certs will have additional SAN entries for any `--apiserver-cert-extra-sans` arguments, lowercased if necessary.
 
 1. Writes kubeconfig files in `/etc/kubernetes/`  for
@@ -177,30 +176,12 @@ The following command can be used to generate a new key on demand:
 kubeadm alpha certs certificate-key
 ```
 
-### Using custom certificates {#custom-certificates}
+### Certificate management with kubeadm
 
-By default, kubeadm generates all the certificates needed for a cluster to run.
-You can override this behavior by providing your own certificates.
-
-To do so, you must place them in whatever directory is specified by the
-`--cert-dir` flag or `CertificatesDir` configuration file key. By default this
-is `/etc/kubernetes/pki`.
-
-If a given certificate and private key pair exists before running `kubeadm init`,
-kubeadm will not overwrite them. This means you can, for example, copy an existing
-CA into `/etc/kubernetes/pki/ca.crt` and `/etc/kubernetes/pki/ca.key`,
-and kubeadm will use this CA for signing the rest of the certificates.
-
-#### External CA mode {#external-ca-mode}
-
-It is also possible to provide just the `ca.crt` file and not the
-`ca.key` file (this is only available for the root CA file, not other cert pairs).
-If all other certificates and kubeconfig files are in place, kubeadm recognizes
-this condition and activates the "External CA" mode. kubeadm will proceed without the
-CA key on disk.
-
-Instead, run the controller-manager standalone with `--controllers=csrsigner` and
-point to the CA certificate and key.
+For detailed information on certificate management with kubeadm see
+[Certificate Management with kubeadm](/docs/tasks/administer-cluster/kubeadm/kubeadm-certs/).
+The document includes information about using external CA, custom certificates
+and certificate renewal.
 
 ### Managing the kubeadm drop-in file for the kubelet {#kubelet-drop-in}
 
diff --git a/content/en/docs/tasks/administer-cluster/kubeadm/kubeadm-certs.md b/content/en/docs/tasks/administer-cluster/kubeadm/kubeadm-certs.md
@@ -21,9 +21,37 @@ You should be familiar with [PKI certificates and requirements in Kubernetes](/d
 
 {{% capture steps %}}
 
+## Using custom certificates {#custom-certificates}
+
+By default, kubeadm generates all the certificates needed for a cluster to run.
+You can override this behavior by providing your own certificates.
+
+To do so, you must place them in whatever directory is specified by the
+`--cert-dir` flag or the `certificatesDir` field of kubeadm's `ClusterConfiguration`.
+By default this is `/etc/kubernetes/pki`.
+
+If a given certificate and private key pair exists before running `kubeadm init`,
+kubeadm does not overwrite them. This means you can, for example, copy an existing
+CA into `/etc/kubernetes/pki/ca.crt` and `/etc/kubernetes/pki/ca.key`,
+and kubeadm will use this CA for signing the rest of the certificates.
+
+## External CA mode {#external-ca-mode}
+
+It is also possible to provide just the `ca.crt` file and not the
+`ca.key` file (this is only available for the root CA file, not other cert pairs).
+If all other certificates and kubeconfig files are in place, kubeadm recognizes
+this condition and activates the "External CA" mode. kubeadm will proceed without the
+CA key on disk.
+
+Instead, run the controller-manager standalone with `--controllers=csrsigner` and
+point to the CA certificate and key.
+
+[PKI certificates and requirements](/docs/setup/best-practices/certificates/) includes guidance on
+setting up a cluster to use an external CA.
+
 ## Check certificate expiration
 
-`check-expiration` can be used to check certificate expiration.
+You can use the `check-expiration` subcommand to check when certificates expire:
 
 ```
 kubeadm alpha certs check-expiration
@@ -32,17 +60,22 @@ kubeadm alpha certs check-expiration
 The output is similar to this:
 
 ```
-CERTIFICATE                EXPIRES                  RESIDUAL TIME   EXTERNALLY MANAGED
-admin.conf                 May 15, 2020 13:03 UTC   364d            false
-apiserver                  May 15, 2020 13:00 UTC   364d            false
-apiserver-etcd-client      May 15, 2020 13:00 UTC   364d            false
-apiserver-kubelet-client   May 15, 2020 13:00 UTC   364d            false
-controller-manager.conf    May 15, 2020 13:03 UTC   364d            false
-etcd-healthcheck-client    May 15, 2020 13:00 UTC   364d            false
-etcd-peer                  May 15, 2020 13:00 UTC   364d            false
-etcd-server                May 15, 2020 13:00 UTC   364d            false
-front-proxy-client         May 15, 2020 13:00 UTC   364d            false
-scheduler.conf             May 15, 2020 13:03 UTC   364d            false
+CERTIFICATE                EXPIRES                  RESIDUAL TIME   CERTIFICATE AUTHORITY   EXTERNALLY MANAGED
+admin.conf                 Dec 30, 2020 23:36 UTC   364d                                    no
+apiserver                  Dec 30, 2020 23:36 UTC   364d            ca                      no
+apiserver-etcd-client      Dec 30, 2020 23:36 UTC   364d            etcd-ca                 no
+apiserver-kubelet-client   Dec 30, 2020 23:36 UTC   364d            ca                      no
+controller-manager.conf    Dec 30, 2020 23:36 UTC   364d                                    no
+etcd-healthcheck-client    Dec 30, 2020 23:36 UTC   364d            etcd-ca                 no
+etcd-peer                  Dec 30, 2020 23:36 UTC   364d            etcd-ca                 no
+etcd-server                Dec 30, 2020 23:36 UTC   364d            etcd-ca                 no
+front-proxy-client         Dec 30, 2020 23:36 UTC   364d            front-proxy-ca          no
+scheduler.conf             Dec 30, 2020 23:36 UTC   364d                                    no
+
+CERTIFICATE AUTHORITY   EXPIRES                  RESIDUAL TIME   EXTERNALLY MANAGED
+ca                      Dec 28, 2029 23:36 UTC   9y              no
+etcd-ca                 Dec 28, 2029 23:36 UTC   9y              no
+front-proxy-ca          Dec 28, 2029 23:36 UTC   9y              no
 ```
 
 The command shows expiration/residual time for the client certificates in the `/etc/kubernetes/pki` folder and for the client certificate embedded in the KUBECONFIG files used by kubeadm (`admin.conf`, `controller-manager.conf` and `scheduler.conf`).
@@ -70,7 +103,7 @@ client-key: /var/lib/kubelet/pki/kubelet-client-current.pem
 
 ## Automatic certificate renewal
 
-`kubeadm` renews all the certificates during control plane [upgrade](/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade/).
+kubeadm renews all the certificates during control plane [upgrade](/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade/).
 
 This feature is designed for addressing the simplest use cases;
 if you don't have specific requirements on certificate renewal and perform Kubernetes version upgrades regularly (less than 1 year in between each upgrade), kubeadm will take care of keeping your cluster up to date and reasonably secure.
