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kubeadm: improvements to the cert management documentation #18397

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Jan 3, 2020
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kubeadm: improvements to the cert management documentation #18397

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6 changes: 3 additions & 3 deletions content/en/docs/reference/setup-tools/kubeadm/implementation-details.md
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Expand Up @@ -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

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31 changes: 6 additions & 25 deletions content/en/docs/reference/setup-tools/kubeadm/kubeadm-init.md
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Expand Up @@ -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
Expand Down Expand Up @@ -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}

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59 changes: 46 additions & 13 deletions content/en/docs/tasks/administer-cluster/kubeadm/kubeadm-certs.md
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Expand Up @@ -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
Expand All @@ -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`).
Expand Down Expand Up @@ -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.
Expand Down