nixpkgs/nixos/doc/manual/configuration/kubernetes.xml

<chapter xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
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         version="5.0"
         xml:id="sec-kubernetes">
 <title>Kubernetes</title>

 <para>
   The NixOS Kubernetes module is a collective term for a handful of
   individual submodules implementing the Kubernetes cluster components.
 </para>

 <para>
   There are generally two ways of enabling Kubernetes on NixOS.
   One way is to enable and configure cluster components appropriately by hand:
<programlisting>
services.kubernetes = {
  apiserver.enable = true;
  controllerManager.enable = true;
  scheduler.enable = true;
  addonManager.enable = true;
  proxy.enable = true;
  flannel.enable = true;
};
</programlisting>
  Another way is to assign cluster roles ("master" and/or "node") to the host.
  This enables apiserver, controllerManager, scheduler, addonManager,
  kube-proxy and etcd:
<programlisting>
<xref linkend="opt-services.kubernetes.roles"/> = [ "master" ];
</programlisting>
  While this will enable the kubelet and kube-proxy only:
<programlisting>
<xref linkend="opt-services.kubernetes.roles"/> = [ "node" ];
</programlisting>
  Assigning both the master and node roles is usable if you want a single
  node Kubernetes cluster for dev or testing purposes:
<programlisting>
<xref linkend="opt-services.kubernetes.roles"/> = [ "master" "node" ];
</programlisting>
  Note: Assigning either role will also default both
  <xref linkend="opt-services.kubernetes.flannel.enable"/> and
  <xref linkend="opt-services.kubernetes.easyCerts"/> to true.
  This sets up flannel as CNI and activates automatic PKI bootstrapping.
 </para>

 <para>
   As of kubernetes 1.10.X it has been deprecated to open
   non-tls-enabled ports on kubernetes components. Thus, from NixOS 19.03 all
   plain HTTP ports have been disabled by default.
   While opening insecure ports is still possible, it is recommended not to
   bind these to other interfaces than loopback.

   To re-enable the insecure port on the apiserver, see options:
   <xref linkend="opt-services.kubernetes.apiserver.insecurePort"/>
   and
   <xref linkend="opt-services.kubernetes.apiserver.insecureBindAddress"/>
 </para>

 <note>
  <para>
   As of NixOS 19.03, it is mandatory to configure:
   <xref linkend="opt-services.kubernetes.masterAddress"/>.
   The masterAddress must be resolveable and routeable by all cluster nodes.
   In single node clusters, this can be set to <literal>localhost</literal>.
  </para>
 </note>

 <para>
   Role-based access control (RBAC) authorization mode is enabled by default.
   This means that anonymous requests to the apiserver secure port will
   expectedly cause a permission denied error. All cluster components must
   therefore be configured with x509 certificates for two-way tls communication.
   The x509 certificate subject section determines the roles and permissions
   granted by the apiserver to perform clusterwide or namespaced operations.
   See also:
   <link
     xlink:href="https://kubernetes.io/docs/reference/access-authn-authz/rbac/">
     Using RBAC Authorization</link>.
 </para>

  <para>
   The NixOS kubernetes module provides an option for automatic certificate
   bootstrapping and configuration,
    <xref linkend="opt-services.kubernetes.easyCerts"/>.
   The PKI bootstrapping process involves setting up a certificate authority
   (CA) daemon (cfssl) on the kubernetes master node. cfssl generates a CA-cert
   for the cluster, and uses the CA-cert for signing subordinate certs issued to
   each of the cluster components. Subsequently, the certmgr daemon monitors
   active certificates and renews them when needed. For single node Kubernetes
   clusters, setting <xref linkend="opt-services.kubernetes.easyCerts"/> = true
   is sufficient and no further action is required. For joining extra node
   machines to an existing cluster on the other hand, establishing initial trust
   is mandatory.
 </para>

 <para>
   To add new nodes to the cluster:
   On any (non-master) cluster node where
   <xref linkend="opt-services.kubernetes.easyCerts"/> is enabled, the helper
   script <literal>nixos-kubernetes-node-join</literal> is available on PATH.
   Given a token on stdin, it will copy the token to the kubernetes
   secrets directory and restart the certmgr service. As requested
   certificates are issued, the script will restart kubernetes cluster
   components as needed for them to pick up new keypairs.
 </para>

 <note>
  <para>
   Multi-master (HA) clusters are not supported by the easyCerts module.
  </para>
 </note>

 <para>
   In order to interact with an RBAC-enabled cluster as an administrator, one
   needs to have cluster-admin privileges. By default, when easyCerts is
   enabled, a cluster-admin kubeconfig file is generated and linked into
   <literal>/etc/kubernetes/cluster-admin.kubeconfig</literal> as determined by
   <xref linkend="opt-services.kubernetes.pki.etcClusterAdminKubeconfig"/>.
   <literal>export KUBECONFIG=/etc/kubernetes/cluster-admin.kubeconfig</literal>
   will make kubectl use this kubeconfig to access and authenticate the cluster.
   The cluster-admin kubeconfig references an auto-generated keypair owned by
   root. Thus, only root on the kubernetes master may obtain cluster-admin
   rights by means of this file.
 </para>

</chapter>