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

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- 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
This commit is contained in:
Lubomir I. Ivanov
2020-01-03 19:45:42 +02:00
committed by Kubernetes Prow Robot
parent 70936d4dbd
commit f510b223e9
3 changed files with 55 additions and 41 deletions
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content/en/docs/reference/setup-tools/kubeadm/implementation-details.md
+3 -3
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@@ -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 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 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. `/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 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 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 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, 3. If kubeadm is running in [external CA mode](/docs/tasks/administer-cluster/kubeadm/kubeadm-certs#external-ca-mode);
because kubeadm cannot generate them by itself 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 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 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
content/en/docs/reference/setup-tools/kubeadm/kubeadm-init.md
+6 -25
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@@ -26,8 +26,7 @@ following steps:
1. Generates a self-signed CA (or using an existing one if provided) to set up 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 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` 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 (`/etc/kubernetes/pki` by default).
[Using custom certificates](#custom-certificates) document.
The APIServer certs will have additional SAN entries for any `--apiserver-cert-extra-sans` arguments, lowercased if necessary. 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 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 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. For detailed information on certificate management with kubeadm see
You can override this behavior by providing your own certificates. [Certificate Management with kubeadm](/docs/tasks/administer-cluster/kubeadm/kubeadm-certs/).
The document includes information about using external CA, custom certificates
To do so, you must place them in whatever directory is specified by the and certificate renewal.
`--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.
### Managing the kubeadm drop-in file for the kubelet {#kubelet-drop-in} ### Managing the kubeadm drop-in file for the kubelet {#kubelet-drop-in}
content/en/docs/tasks/administer-cluster/kubeadm/kubeadm-certs.md
+46 -13
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@@ -21,9 +21,37 @@ You should be familiar with [PKI certificates and requirements in Kubernetes](/d
{{% capture steps %}} {{% 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 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 kubeadm alpha certs check-expiration
@@ -32,17 +60,22 @@ kubeadm alpha certs check-expiration
The output is similar to this: The output is similar to this:
``` ```
CERTIFICATE EXPIRES RESIDUAL TIME EXTERNALLY MANAGED CERTIFICATE EXPIRES RESIDUAL TIME CERTIFICATE AUTHORITY EXTERNALLY MANAGED
admin.conf May 15, 2020 13:03 UTC 364d false admin.conf Dec 30, 2020 23:36 UTC 364d no
apiserver May 15, 2020 13:00 UTC 364d false apiserver Dec 30, 2020 23:36 UTC 364d ca no
apiserver-etcd-client May 15, 2020 13:00 UTC 364d false apiserver-etcd-client Dec 30, 2020 23:36 UTC 364d etcd-ca no
apiserver-kubelet-client May 15, 2020 13:00 UTC 364d false apiserver-kubelet-client Dec 30, 2020 23:36 UTC 364d ca no
controller-manager.conf May 15, 2020 13:03 UTC 364d false controller-manager.conf Dec 30, 2020 23:36 UTC 364d no
etcd-healthcheck-client May 15, 2020 13:00 UTC 364d false etcd-healthcheck-client Dec 30, 2020 23:36 UTC 364d etcd-ca no
etcd-peer May 15, 2020 13:00 UTC 364d false etcd-peer Dec 30, 2020 23:36 UTC 364d etcd-ca no
etcd-server May 15, 2020 13:00 UTC 364d false etcd-server Dec 30, 2020 23:36 UTC 364d etcd-ca no
front-proxy-client May 15, 2020 13:00 UTC 364d false front-proxy-client Dec 30, 2020 23:36 UTC 364d front-proxy-ca no
scheduler.conf May 15, 2020 13:03 UTC 364d false 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`). 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 ## 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; 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. 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.