| title | reviewers | content_type | weight | |
|---|---|---|---|---|
PKI certificates and requirements |
|
concept |
50 |
Kubernetes requires PKI certificates for authentication over TLS. If you install Kubernetes with kubeadm, the certificates that your cluster requires are automatically generated. You can also generate your own certificates -- for example, to keep your private keys more secure by not storing them on the API server. This page explains the certificates that your cluster requires.
Kubernetes requires PKI for the following operations:
- Client certificates for the kubelet to authenticate to the API server
- Kubelet server certificates for the API server to talk to the kubelets
- Server certificate for the API server endpoint
- Client certificates for administrators of the cluster to authenticate to the API server
- Client certificates for the API server to talk to the kubelets
- Client certificate for the API server to talk to etcd
- Client certificate/kubeconfig for the controller manager to talk to the API server
- Client certificate/kubeconfig for the scheduler to talk to the API server.
- Client and server certificates for the front-proxy
{{< note >}}
front-proxy certificates are required only if you run kube-proxy to support
an extension API server.
{{< /note >}}
etcd also implements mutual TLS to authenticate clients and peers.
If you install Kubernetes with kubeadm, most certificates are stored in /etc/kubernetes/pki.
All paths in this documentation are relative to that directory, with the exception of user account
certificates which kubeadm places in /etc/kubernetes.
If you don't want kubeadm to generate the required certificates, you can create them using a single root CA or by providing all certificates. See Certificates for details on creating your own certificate authority. See Certificate Management with kubeadm for more on managing certificates.
You can create a single root CA, controlled by an administrator. This root CA can then create multiple intermediate CAs, and delegate all further creation to Kubernetes itself.
Required CAs:
| path | Default CN | description |
|---|---|---|
| ca.crt,key | kubernetes-ca | Kubernetes general CA |
| etcd/ca.crt,key | etcd-ca | For all etcd-related functions |
| front-proxy-ca.crt,key | kubernetes-front-proxy-ca | For the front-end proxy |
On top of the above CAs, it is also necessary to get a public/private key pair for service account
management, sa.key and sa.pub.
The following example illustrates the CA key and certificate files shown in the previous table:
/etc/kubernetes/pki/ca.crt
/etc/kubernetes/pki/ca.key
/etc/kubernetes/pki/etcd/ca.crt
/etc/kubernetes/pki/etcd/ca.key
/etc/kubernetes/pki/front-proxy-ca.crt
/etc/kubernetes/pki/front-proxy-ca.key
If you don't wish to copy the CA private keys to your cluster, you can generate all certificates yourself.
Required certificates:
| Default CN | Parent CA | O (in Subject) | kind | hosts (SAN) |
|---|---|---|---|---|
| kube-etcd | etcd-ca | server, client | <hostname>, <Host_IP>, localhost, 127.0.0.1 |
|
| kube-etcd-peer | etcd-ca | server, client | <hostname>, <Host_IP>, localhost, 127.0.0.1 |
|
| kube-etcd-healthcheck-client | etcd-ca | client | ||
| kube-apiserver-etcd-client | etcd-ca | client | ||
| kube-apiserver | kubernetes-ca | server | <hostname>, <Host_IP>, <advertise_IP>, [1] |
|
| kube-apiserver-kubelet-client | kubernetes-ca | system:masters | client | |
| front-proxy-client | kubernetes-front-proxy-ca | client |
{{< note >}}
Instead of using the super-user group system:masters for kube-apiserver-kubelet-client
a less privileged group can be used. kubeadm uses the kubeadm:cluster-admins group for
that purpose.
{{< /note >}}
[1]: any other IP or DNS name you contact your cluster on (as used by kubeadm
the load balancer stable IP and/or DNS name, kubernetes, kubernetes.default, kubernetes.default.svc,
kubernetes.default.svc.cluster, kubernetes.default.svc.cluster.local)
where kind maps to one or more of the x509 key usage, which is also documented in the
.spec.usages of a CertificateSigningRequest
type:
| kind | Key usage |
|---|---|
| server | digital signature, key encipherment, server auth |
| client | digital signature, key encipherment, client auth |
{{< note >}} Hosts/SAN listed above are the recommended ones for getting a working cluster; if required by a specific setup, it is possible to add additional SANs on all the server certificates. {{< /note >}}
{{< note >}} For kubeadm users only:
- The scenario where you are copying to your cluster CA certificates without private keys is referred as external CA in the kubeadm documentation.
- If you are comparing the above list with a kubeadm generated PKI, please be aware that
kube-etcd,kube-etcd-peerandkube-etcd-healthcheck-clientcertificates are not generated in case of external etcd.
{{< /note >}}
Certificates should be placed in a recommended path (as used by kubeadm). Paths should be specified using the given argument regardless of location.
| Default CN | recommended key path | recommended cert path | command | key argument | cert argument |
|---|---|---|---|---|---|
| etcd-ca | etcd/ca.key | etcd/ca.crt | kube-apiserver | --etcd-cafile | |
| kube-apiserver-etcd-client | apiserver-etcd-client.key | apiserver-etcd-client.crt | kube-apiserver | --etcd-keyfile | --etcd-certfile |
| kubernetes-ca | ca.key | ca.crt | kube-apiserver | --client-ca-file | |
| kubernetes-ca | ca.key | ca.crt | kube-controller-manager | --cluster-signing-key-file | --client-ca-file, --root-ca-file, --cluster-signing-cert-file |
| kube-apiserver | apiserver.key | apiserver.crt | kube-apiserver | --tls-private-key-file | --tls-cert-file |
| kube-apiserver-kubelet-client | apiserver-kubelet-client.key | apiserver-kubelet-client.crt | kube-apiserver | --kubelet-client-key | --kubelet-client-certificate |
| front-proxy-ca | front-proxy-ca.key | front-proxy-ca.crt | kube-apiserver | --requestheader-client-ca-file | |
| front-proxy-ca | front-proxy-ca.key | front-proxy-ca.crt | kube-controller-manager | --requestheader-client-ca-file | |
| front-proxy-client | front-proxy-client.key | front-proxy-client.crt | kube-apiserver | --proxy-client-key-file | --proxy-client-cert-file |
| etcd-ca | etcd/ca.key | etcd/ca.crt | etcd | --trusted-ca-file, --peer-trusted-ca-file | |
| kube-etcd | etcd/server.key | etcd/server.crt | etcd | --key-file | --cert-file |
| kube-etcd-peer | etcd/peer.key | etcd/peer.crt | etcd | --peer-key-file | --peer-cert-file |
| etcd-ca | etcd/ca.crt | etcdctl | --cacert | ||
| kube-etcd-healthcheck-client | etcd/healthcheck-client.key | etcd/healthcheck-client.crt | etcdctl | --key | --cert |
Same considerations apply for the service account key pair:
| private key path | public key path | command | argument |
|---|---|---|---|
| sa.key | kube-controller-manager | --service-account-private-key-file | |
| sa.pub | kube-apiserver | --service-account-key-file |
The following example illustrates the file paths from the previous tables you need to provide if you are generating all of your own keys and certificates:
/etc/kubernetes/pki/etcd/ca.key
/etc/kubernetes/pki/etcd/ca.crt
/etc/kubernetes/pki/apiserver-etcd-client.key
/etc/kubernetes/pki/apiserver-etcd-client.crt
/etc/kubernetes/pki/ca.key
/etc/kubernetes/pki/ca.crt
/etc/kubernetes/pki/apiserver.key
/etc/kubernetes/pki/apiserver.crt
/etc/kubernetes/pki/apiserver-kubelet-client.key
/etc/kubernetes/pki/apiserver-kubelet-client.crt
/etc/kubernetes/pki/front-proxy-ca.key
/etc/kubernetes/pki/front-proxy-ca.crt
/etc/kubernetes/pki/front-proxy-client.key
/etc/kubernetes/pki/front-proxy-client.crt
/etc/kubernetes/pki/etcd/server.key
/etc/kubernetes/pki/etcd/server.crt
/etc/kubernetes/pki/etcd/peer.key
/etc/kubernetes/pki/etcd/peer.crt
/etc/kubernetes/pki/etcd/healthcheck-client.key
/etc/kubernetes/pki/etcd/healthcheck-client.crt
/etc/kubernetes/pki/sa.key
/etc/kubernetes/pki/sa.pub
You must manually configure these administrator account and service accounts:
| filename | credential name | Default CN | O (in Subject) |
|---|---|---|---|
| admin.conf | default-admin | kubernetes-admin | <admin-group> |
| super-admin.conf | default-super-admin | kubernetes-super-admin | system:masters |
| kubelet.conf | default-auth | system:node:<nodeName> (see note) |
system:nodes |
| controller-manager.conf | default-controller-manager | system:kube-controller-manager | |
| scheduler.conf | default-scheduler | system:kube-scheduler |
{{< note >}}
The value of <nodeName> for kubelet.conf must match precisely the value of the node name
provided by the kubelet as it registers with the apiserver. For further details, read the
Node Authorization.
{{< /note >}}
{{< note >}}
In the above example <admin-group> is implementation specific. Some tools sign the
certificate in the default admin.conf to be part of the system:masters group.
system:masters is a break-glass, super user group can bypass the authorization
layer of Kubernetes, such as RBAC. Also some tools do not generate a separate
super-admin.conf with a certificate bound to this super user group.
kubeadm generates two separate administrator certificates in kubeconfig files.
One is in admin.conf and has Subject: O = kubeadm:cluster-admins, CN = kubernetes-admin.
kubeadm:cluster-admins is a custom group bound to the cluster-admin ClusterRole.
This file is generated on all kubeadm managed control plane machines.
Another is in super-admin.conf that has Subject: O = system:masters, CN = kubernetes-super-admin.
This file is generated only on the node where kubeadm init was called.
{{< /note >}}
-
For each config, generate an x509 cert/key pair with the given CN and O.
-
Run
kubectlas follows for each config:
KUBECONFIG=<filename> kubectl config set-cluster default-cluster --server=https://<host ip>:6443 --certificate-authority <path-to-kubernetes-ca> --embed-certs
KUBECONFIG=<filename> kubectl config set-credentials <credential-name> --client-key <path-to-key>.pem --client-certificate <path-to-cert>.pem --embed-certs
KUBECONFIG=<filename> kubectl config set-context default-system --cluster default-cluster --user <credential-name>
KUBECONFIG=<filename> kubectl config use-context default-system
These files are used as follows:
| filename | command | comment |
|---|---|---|
| admin.conf | kubectl | Configures administrator user for the cluster |
| super-admin.conf | kubectl | Configures super administrator user for the cluster |
| kubelet.conf | kubelet | One required for each node in the cluster. |
| controller-manager.conf | kube-controller-manager | Must be added to manifest in manifests/kube-controller-manager.yaml |
| scheduler.conf | kube-scheduler | Must be added to manifest in manifests/kube-scheduler.yaml |
The following files illustrate full paths to the files listed in the previous table:
/etc/kubernetes/admin.conf
/etc/kubernetes/super-admin.conf
/etc/kubernetes/kubelet.conf
/etc/kubernetes/controller-manager.conf
/etc/kubernetes/scheduler.conf